[CTF] Pragyan CTF - Forensics Writeup

Hy Friends , this time i played Pragyan CTF 2022 and my team scored 8th place. This CTF was pretty crazy. We solved all forensics challenges , Good Job @Vyshak and @Paul

Ye Olde Threat

intel.txt have string aHR0cHM6Ly9kcml2ZS5nb29nbGUuY29tL2ZpbGUvZC8xQUVremJqV1JDZFVwNEY3ZjJ3dExnSWQyd2RTRlkwUXE=.

Convert this Base64 string to get a Gdrive URL.

It gives a zip file named intel.zip and inside it have a PNG image.

Tried to open the image but gave error , So it must be corrupted. Open it in hexeditor.

We can see the PNG header is missing also IHDR isn’t correct , IDAT also named as Ida7.

After fixing those we get a half-earth image.

Check the image with pngcheck, pngcheck -v Just_A_Plane_Image.png.

Here the length of second IDAT is really weird, Its over the size of the png file itself.

Search the second IDAT and set the length value to 00 00 20 00 which is 8192 bytes , same as previous IDAT chunk.

Now once again do pngcheck, this time it shows CRC error.

Fix the CRC using PCR tool, python2 PCRT.py -v -i Just_A_Plane_Image.png and open the output.png in stegsolve.


Frank’s Little Beauty

First of all , dump password hashes to a file

vol.py -f MemDump.DMP --profile=Win7SP1x64 hashdump > hashes

We got Frank’s password hash : Frank Reynolds:1000:aad3b435b51404eeaad3b435b51404ee:a88d1e18706d3aa676e01e5943d15911:::.

Crack the hash a88d1e18706d3aa676e01e5943d15911 using crackstation , the cracked password is trolltoll. This password will be needed later because as of Description , frank reuses password so this will come in handy to extract zips or like that.

The decription have frank is lazy to type , one of the crucial area in a memory dump is clipboard . Lets see whats inside the clipboard of this memory dump.

vol.py -f MemDump.DMP --profile=Win7SP1x64 clipboard

We got a pastebin link https://pastebin.com/3Ecrm2DY

flag 1/3 : p_ctf{v0l4t1l1ty

Now dig more to find remaining parts. Next area to check is process command lines.

vol.py -f MemDump.DMP --profile=Win7SP1x64 cmdline > cmdlog

writing results to a file is always a good practice, so no need to rescan all time.

pid:   2200
Command line : "C:\Program Files\WinRAR\WinRAR.exe"  e comp.rar

comp.rar is interesting , but we can’t get file from cmdline , To get files first we need to do a scan , then dump file using its Offset.

vol -f MemDump.DMP --profile=Win7SP1x64 filescan > scanlog

Found offset 0x000000003df4e450 for comp.rar , now dump the file from memory.

vol -f MemDump.DMP --profile=Win7SP1x64 dumpfiles -D . -Q 0x000000003df4e450

Its a password protected rar file , extract the file using trolltoll as password. It gives a image file which have 2nd part of the flag.

Last flag must be related to the Paddys in description. He don’t remember shortcut to Paddys.

Search for .lnk in the scanlog. Assumption was correct , there exists Paddys.lnk shortcut file and its offset is 0x000000003e1891d0.

vol -f MemDump.DMP --profile=Win7SP1x64 dumpfiles -D . 0x000000003e1891d0

Its a shortcut to C:\Program Files\Microsoft Games\Minesweeper\sysinfo.txt. Check the cmdlog to see if any process opened this file. Its currently opened by a notepad process.

pid:   3016
Command line : "C:\Windows\system32\NOTEPAD.EXE" C:\Program Files\Microsoft Game

Tried to extract this file using offset , but that didn’t worked. Since its opened by Notepad dumping the notepad process should give its contents.

vol -f MemDump.DMP --profile=Win7SP1x64 memdump -p 3016 -D .

Notepad uses UTF-16 to store texts , so grep through the memdump of notepad.

strings -e l 3016.dmp | less

flag part 3/3 : _r34d1ng_dump5_iasip}


Marcel and the iPad

This challenge is similar to Bobby toes iPad. Googling is really useful :).

Stegsolve the marcel.png.

This is a one-time-pad message.

Message : 1h@ww_e0op$_0b_t0y

Pad is at the Comment section of exif of the image.

Pad : Steve_loves_apple

Decrypt using OTP tool.


Hidden and Protected

The description don’t have much suspicious info , although the title is interesting.

Firstly do binwalk.

We can see a zip file there, we can use foremost or binwalk itself to get that file.

foremost image.png

Inside the zip there is another image and its in JPG format , We have complied with first section of Title , that is Hidden.

So next part is protected, Since this is a JPG it should be a stegofile. Zip also have a text file , but didn’t bothered about it.

Using stegseek crack the stegofile.

stegseek image2.jpg /usr/share/wordlists/rockyou.txt

Zipped scandal

We are given with a zip file named Aa.zip, extracting it gives Ab.zip and doing the same on it gives Ac.zip , so its like onion zipped many times.

But the pattern is Aa, Ab, Ac , first letter Uppercase and second letter Lowercase. Here is a way to extract the zip file.

from os import system
import string
from string import *

system("cp Aa.zip .nvm.zip")
for i in a:
    for j in b:
        system(f'unzip {i+j}.zip ')
        system(f'rm {i+j}.zip')

It extracts all the zip files upto Zz.zip. Finally we are left with Checkpoint.zip. Extracting it gives an image and another zip.

Final.zip is password protected. Looking at exif of the image , we get a hash in comment section and GPS coordinates.

Cracking hash using crackstation gives SHA256. Next is to find the Location 36°20' 21.49" N, 96°48' 10.32" W. Paste the location cords in Google Map.

The location is Pawnee City Hall.

Tried this as password to extract Final.zip , but no success. So connect SHA256 with this result , that is Hash the location name in sha256.

Thats the password , then it gives a black image.

Change its bit plane and it gives a QR with black background and white foreground. Its still not good , so invert the color to make it normal QR Code.

This QR points to Gdrive link zipped.zip

The zip includes an audio and a hint.txt , Audio sounds like morse code , so tried to decode it and it gave gibberish message.

Looking at the hint "Fast as we can. Really put the pedal to the metal, you know! Bill and Ted did it." , at first it didn’t made any sense.

After some googling , found out that its an excerpt from Ready Player One Movie , Why can't we go backwards for once? Backwards, really fast. Fast as we can. Really, put the pedal to the metal, you know?.

Now the hint makes much sense , reverse the audio and decode it again.