## Hint Whoops. TrID is a more sophisticated version of file. There are many other tools available that will help you with steganography challenges. Once again, a Python toolset exists for the examination and analysis of OLE and OOXML documents: oletools. Another is a framework in Ruby called Origami. Not bad. In the case where you do need to understand a complicated VBA macro, or if the macro is obfuscated and has an unpacker routine, you don't need to own a license to Microsoft Office to debug this. A tag already exists with the provided branch name. Audacity can also enable you to slow down, reverse, and do other manipulations that might reveal a hidden message if you suspect there is one (if you can hear garbled audio, interference, or static). :::danger Now running command in terminal $ pngcheck mystery mystery invalid chunk length (too large) |Hexa Values|Ascii Translation| We found this file. mystery ffmpeg -i gives initial analysis of the file content. Le flag est sous la forme APRK{SHA1(NOMPRENOM)}. Your file will be uploaded and we'll show you file's defects with preview. By rejecting non-essential cookies, Reddit may still use certain cookies to ensure the proper functionality of our platform. This online WebP image compressor for professionals compresses your image and photos to the smallest filesize possible. The majority of challenges you encounter will not be as easy in the examples above. Example 2: You are given a file named solitaire.exe. |-|-| Stellar Repair for Photo sign in Based on the output, the 19th key value must be 0x3 and the 20th key must be 0xbe. Me and my team, Tower of Hanoi, have played the PlaidCTF 2015: while my teammates did reversing stuff, my friend john and I did this awesome forensic challenge. ERRORS DETECTED in mystery_solved_v1.png All of these tools, however, are made to analyze non-corrupted and well-formatted files. It is also extensible using plugins for extracting various types of artifact. When the run Window appears, type cmd and press the Enter button. A popular CTF challenge is to provide a PCAP file representing some network traffic and challenge the player to recover/reconstitute a transferred file or transmitted secret. 00000050: 52 24 f0 00 00 ff a5 49 44 41 54 78 5e ec bd 3f R$..IDATx^..? Didier Stevens has written good introductory material about the format. Reading a file into a bytearray for processing: What follows is a high-level overview of some of the common concepts in forensics CTF challenges, and some recommended tools for performing common tasks. I H D R. Now file recognizes successfully that the file is a PNG $ file Challenge Challenge: PNG image data, 1920 x 1289, 8-bit/color RGB, interlaced I still wasn't able to read it. This is what is referred to as binary-to-text encoding, a popular trope in CTF challenges. D E T`| Microsoft Office document forensic analysis is not too different from PDF document forensics, and just as relevant to real-world incident response. The difficulty with steganography is that extracting the hidden message requires not only a detection that steganography has been used, but also the exact steganographic tool used to embed it. By default, it only checks headers of the file for better performance. An open-source alternative has emerged called Kaitai. The binary objects can be compressed or even encrypted data, and include content in scripting languages like JavaScript or Flash. Written by Maltemo, member of team SinHack. P N G`| We wrote the script and it took a lifetime. As with image file formats, stegonagraphy might be used to embed a secret message in the content data, and again you should know to check the file metadata areas for clues. PHPGIFpngJPEG; PHPForA-Z26AA,AB,AC; WebPHPCodeigniter; Ubuntu PHP; EosPHP; ctfphp View all strings in the file with strings -n 7 -t x filename.png. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. 00000050: 52 24 f0 aa aa ff a5 ab 44 45 54 78 5e ec bd 3f R$DETx^..? Made for fixed-function low-resource environments, they can be compressed, single-file, or read-only. One would typically not bust a criminal case by carefully reassembling a corrupted PNG file, revealing a photo of a QR code that decodes to a password for a zip archive containing an NES rom that when played will output the confession. Gimp provides the ability to alter various aspects of the visual data of an image file. :smile: Nice, we just get the same values at the end of the wrong length. Example 2: You are given a file named solitaire.exe.Running the file command reveals the following: The file command show this is a PNG file and not an executable file. CTF Example WDCTF-finals-2017 Download the challenge here If you look at the file, you can see that the header and width of the PNG file are incorrect. 1642 x 1095 image, 24-bit RGB, non-interlaced File is CORRUPTED. Viewing the image, we get the flag: picoCTF{c0rrupt10n_1847995}. It was probably transmitted in text mode. It's no longer available at its original URL, but you can find a copy here. When an image is downloaded as text through FTP (ASCII Mode), each 0x0D 0x0A bytes tuple (\r\n) is truncated to 0x0A. If you have any questions feel free to Tweet or PM me @mrkmety. # L | IDAT | DATA | CHECKSUM ---> {L} {DATA, CHECKSUM, L} {DATA, CHECKSUM, L} {DATA, CHECKSUM} Hidden in the meta-information is a field named Comment. A note about PCAP vs PCAPNG: there are two versions of the PCAP file format; PCAPNG is newer and not supported by all tools. |`0A`| **A Unix-style line ending (LF) to detect Unix-DOS line ending conversion. |-|-| To verify correcteness or attempt to repair corrupted PNGs you can use pngcheck. author: Maltemo Run the following command to install exiftool. (In progress) tags: ctflearn - CTF - forensics. ## Analyzing the file Decompile compiled python binaries (exe, elf) - Retreive from .pyc, Checklist - Local Windows Privilege Escalation, Pentesting JDWP - Java Debug Wire Protocol, 161,162,10161,10162/udp - Pentesting SNMP, 515 - Pentesting Line Printer Daemon (LPD), 548 - Pentesting Apple Filing Protocol (AFP), 1098/1099/1050 - Pentesting Java RMI - RMI-IIOP, 1433 - Pentesting MSSQL - Microsoft SQL Server, 1521,1522-1529 - Pentesting Oracle TNS Listener, 2301,2381 - Pentesting Compaq/HP Insight Manager, 3690 - Pentesting Subversion (svn server), 4369 - Pentesting Erlang Port Mapper Daemon (epmd), 8009 - Pentesting Apache JServ Protocol (AJP), 8333,18333,38333,18444 - Pentesting Bitcoin, 9100 - Pentesting Raw Printing (JetDirect, AppSocket, PDL-datastream), 10000 - Pentesting Network Data Management Protocol (ndmp), 24007,24008,24009,49152 - Pentesting GlusterFS, 50030,50060,50070,50075,50090 - Pentesting Hadoop, Reflecting Techniques - PoCs and Polygloths CheatSheet, Dangling Markup - HTML scriptless injection, HTTP Request Smuggling / HTTP Desync Attack, Regular expression Denial of Service - ReDoS, Server Side Inclusion/Edge Side Inclusion Injection, XSLT Server Side Injection (Extensible Stylesheet Languaje Transformations), Pentesting CI/CD (Github, Jenkins, Terraform), Windows Exploiting (Basic Guide - OSCP lvl), INE Courses and eLearnSecurity Certifications Reviews, Stealing Sensitive Information Disclosure from a Web, PNG files, in particular, are popular in CTF challenges, probably for their lossless compression suitable for hiding non-visual data in the image. We are given a PNG image that is corrupted in some way. Written by Maltemo, member of team SinHack. In some cases, it is possible to fix and recover the corrupt jpeg/jpg, gif, tiff, bmp, png, raw (JPEG, GIF89a, GIF87a, BMP, TIFF, PNG and RAW) file. Also, network (packet capture) forensics is more about metadata analysis than content analysis, as most network sessions are TLS-encrypted between endpoints now. . It's also common to check least-significant-bits (LSB) for a secret message. CTF PNG Critical Chunk Size Fixer This is a tool I created intended to be used in forensics challenges for CTFs where you are given a corrupted PNG file. Exiftool We start by inspecting the metadata with exiftool:. You may not be looking for a file in the visible filesystem at all, but rather a hidden volume, unallocated space (disk space that is not a part of any partition), a deleted file, or a non-file filesystem structure like an http://www.nirsoft.net/utils/alternate_data_streams.html. Keep in mind that heuristics, and tools that employ them, can be easily fooled. The NSA wrote a guide to these hiding places in 2008 titled "Hidden Data and Metadata in Adobe PDF Files: Publication Risks and Countermeasures." It looks like someone dumped our database. Many file formats are well-described in the public documentation you can find with a web search, but having some familiarity with the file format specifications will also help, so we include links to those here. * For more in depth knowledge about how works chunks in PNG, I strongly recommend you two read my other write-ups that explains a lot of things : Corrupted PNG . ___ There are many Base64 encoder/decoders online, or you can use the base64 command: ASCII-encoded hexadecimal is also identifiable by its charset (0-9, A-F). The PNG header had End Of Line specific that wasn't recognized on Linux. Something to do with the file header Whatever that is. A PNG image has a lot of blocks, called chunks, which have the same structure: The most important one, which actually represents the image, is called IDAT. Palindrome must have leaked one of their passwords as the 4 corrupted bytes (Part 1 flag)! Bad news ahead: by opening the image we were greeted by a fantastic 960x600 black image. ``` You can even start a macro of a specific document from a command line: its ability to analyze certain media file formats like GIF, JPG, and PNG, http://www.nirsoft.net/utils/alternate_data_streams.html, dpkt Python package for pcap manipulation, typically just used as a jumping-off platform to bootstrap code execution, Knowing a scripting language (e.g., Python), Knowing how to manipulate binary data (byte-level manipulations) in that language, Recognizing formats, protocols, structures, and encodings, Video (especially MP4) or Audio (especially WAV, MP3), Microsoft's Office formats (RTF, OLE, OOXML), the "incremental generation" feature of PDF wherein a previous version is retained but not visible to the user. We intercepted this image, but it must have gotten corrupted during the transmission. Paste a Base64 Data URI from your clipboard into this website. Therefore, we get the length of 0x10004 - 0x5B - 0x4 = 0xFFA5 which is good since the original value is 0xAAAAFFA5. When you are on the file, search for known elements that give hints about the file type. file won't recognize it, but inspecting the header we can see strings which are common in PNG files. --- To verify the correctness or attempt to repair corrupted PNGs you can use, You can try to repair corrupted PNGs using online tools like, https://online.officerecovery.com/pixrecovery/. ## Flag Sometimes the challenge is not to find hidden static data, but to analyze a VBA macro to determine its behavior. A collection of write-ups from the best hackers in the world on topics ranging from bug bounties and CTFs to vulnhub machines, hardware challenges and real life encounters. If one thing doesnt work then you move on to the next until you find something that does work. If you want to write your own scripts to process PCAP files directly, the dpkt Python package for pcap manipulation is recommended. Flags may be hidden in the meta information and can easily be read by running exiftool. The premiere open-source framework for memory dump analysis is Volatility. There are a handful of command-line tools for zip files that will be useful to know about. There is a hint with the `D` and `T` letters, which help us to deduce that it is a `IDAT` chunk. As far as that is possible, all formats supported by the PNG standard are represented. |-|-| PNGPythonGUIPySimpleGUICTFerCTFpng10. It would be impossible to prepare for every possible data format, but there are some that are especially popular in CTFs. Hello, I am doing forensics CTF challenges and wanted to get some advice on how to investigate the images. The third byte is "delta Y", with down (toward the user) being negative. It's possible, but it would entail identifying every possible byte sequence that might have been . Thank you javier. Long story short, heres what we did next: PS: I know that some of you was wondering how wonderful our script wasso have a good headache after it ;-). chunk pHYs at offset 0x00042, length 9: 2852132389x5669 pixels/meter For everything else, there's TestDisk: recover missing partition tables, fix corrupted ones, undelete files on FAT or NTFS, etc. |-|-| Files-within-files is a common trope in forensics CTF challenges, and also in embedded systems' firmware where primitive or flat filesystems are common. Subscribe to our weekly newsletter for the coolest infosec updates: https://weekly.infosecwriteups.com/, Cybersecurity Enthusiast | Cloud Security & Information Protection @ Boeing | Trying to pass on knowledge to others | www.thecyberblog.com. I've then assumed it was a corrupted PNG and saw that the first bytes where wrong instead of . But most of the time, as the file is corrupted, you will obtain this answer : data. `89 50 4E 47 0D 0A B0 AA` After a little time of thinking, I finally found what was wrong. According to the [PNG specs], the first 8 bytes of the file are constant, so let's go ahead and fix that: . I hereby ask you to accept the. So, given the memory dump file and the relevant "profile" (the OS from which the dump was gathered), Volatility can start identifying the structures in the data: running processes, passwords, etc. ..A. 00000070: f9 ed 40 a0 f3 6e 40 7b 90 23 8f 1e d7 20 8b 3e ..@..n@{.# .>. 00000000: 8950 4e47 0d0a 1a0a .PNG. corrupt.png.fix additional data after IEND chunk, corrupt.png.fix: PNG image data, 500 x 408, 8-bit/color RGBA, non-interlaced, 500 x 408 image, 32-bit RGB+alpha, non-interlaced, red = 0x00ff, green = 0x00ff, blue = 0x00ff, chunk pHYs at offset 0x00037, length 9: 2835x2835 pixels/meter (72 dpi), chunk tIME at offset 0x0004c, length 7: 20 Jun 2016 03:20:08 UTC, chunk IDAT at offset 0x0005f, length 8192, zlib: deflated, 32K window, maximum compression, chunk IDAT at offset 0x0206b, length 8192, chunk IDAT at offset 0x04077, length 8192, chunk IDAT at offset 0x06083, length 8192, chunk IDAT at offset 0x0808f, length 8192, chunk IDAT at offset 0x0a09b, length 8192, chunk IDAT at offset 0x0c0a7, length 8192, chunk IDAT at offset 0x0e0b3, length 8192, chunk IDAT at offset 0x100bf, length 8192, chunk IDAT at offset 0x120cb, length 8192, chunk IDAT at offset 0x140d7, length 8192, chunk IDAT at offset 0x160e3, length 8192, chunk IDAT at offset 0x180ef, length 8192, chunk IDAT at offset 0x1a0fb, length 8192, chunk IDAT at offset 0x1c107, length 8192, chunk IDAT at offset 0x1e113, length 8192, chunk IDAT at offset 0x2011f, length 8192, chunk IDAT at offset 0x2212b, length 8192, chunk IDAT at offset 0x24137, length 8192, chunk IDAT at offset 0x26143, length 8192, chunk IDAT at offset 0x2814f, length 8192, chunk IDAT at offset 0x2a15b, length 8192, chunk IDAT at offset 0x2c167, length 8192, chunk IDAT at offset 0x2e173, length 8192, chunk IDAT at offset 0x3017f, length 8192, chunk IDAT at offset 0x3218b, length 8192, chunk IDAT at offset 0x34197, length 8192, chunk IDAT at offset 0x361a3, length 8192, chunk IDAT at offset 0x381af, length 8192, chunk IDAT at offset 0x3a1bb, length 8192, chunk IDAT at offset 0x3c1c7, length 8192, chunk IDAT at offset 0x3e1d3, length 8192, chunk IDAT at offset 0x401df, length 8192, chunk IDAT at offset 0x421eb, length 8192, chunk IDAT at offset 0x441f7, length 8192, chunk IDAT at offset 0x46203, length 8192, chunk IDAT at offset 0x4820f, length 8192, chunk IDAT at offset 0x4a21b, length 8192, chunk IDAT at offset 0x4c227, length 8192, chunk IDAT at offset 0x4e233, length 8192, chunk IDAT at offset 0x5023f, length 8192, chunk IDAT at offset 0x5224b, length 8192, chunk IDAT at offset 0x54257, length 8192, chunk IDAT at offset 0x56263, length 8192, chunk IDAT at offset 0x5826f, length 8192, chunk IDAT at offset 0x5a27b, length 8192, chunk IDAT at offset 0x5c287, length 8192, chunk IDAT at offset 0x5e293, length 8192, chunk IDAT at offset 0x6029f, length 8192, chunk IDAT at offset 0x622ab, length 8192, chunk IDAT at offset 0x642b7, length 8192, chunk IDAT at offset 0x662c3, length 8192, chunk IDAT at offset 0x682cf, length 8192, chunk IDAT at offset 0x6a2db, length 8192, chunk IDAT at offset 0x6c2e7, length 8192, chunk IDAT at offset 0x6e2f3, length 8192, chunk IDAT at offset 0x702ff, length 8192, chunk IDAT at offset 0x7230b, length 1619. You can extract hidden files by running the following command. I broke my solution down into 5 steps: Read the corrupted PNG into memory. the "cover text"), is extraordinarily rare in the real world (made effectively obsolete by strong cryptography), but is another popular trope in CTF forensics challenges. Forensics is a broad CTF category that does not map well to any particular job role in the security industry, although some challenges model the kinds of tasks seen in Incident Response (IR). Written by Maltemo, member of team SinHack Help! check the header format has the hint says and edit the header format After that try to open the file and see what goes on, After that you can use the gif speed control online and slow the speed of the encoded message and finally your get the message but being encoded. It was easy to understand we had to repair a PNG file, but first, we checked what we had in our hands. The challenge intends to hide the flag. Hello, welcome on "Containment Forever"! There are plugins for extracting SQL databases, Chrome history, Firefox history and much more. Run the following command to install binwalk. In this way, it is often even possible to recover image data that has been intentionally disturbed, e.g. We can read `0xffa5 bytes`. ctf. There might be a gold mine of metadata, or there might be almost nothing. CTF challenge authors have historically used altered Hue/Saturation/Luminance values or color channels to hide a secret message. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Dig deeper to find what was hidden! The file command show this is a PNG file and not an executable file. PNG files can be dissected in Wireshark. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. If trying to repair a damaged PCAP file, there is an online service for repairing PCAP files called PCAPfix. But malicious VBA macros are rarely complicated, since VBA is typically just used as a jumping-off platform to bootstrap code execution. Just as "file carving" refers to the identification and extraction of files embedded within files, "packet carving" is a term sometimes used to describe the extraction of files from a packet capture. We use -n 7 for strings of length 7+, and -t x to view- their position in the file. What we thought was: the LENGTH section indicates how many bytes should have been in the chunk in the first place so we compared that value with the actual length of the corrupted image DATA section. The big image compression tool comparison. This disconnect between the somewhat artificial puzzle-game CTF "Forensics" and the way that forensics is actually done in the field might be why this category does not receive as much attention as the vulnerability-exploitation style challenges. Also, if a file contains another file embedded somewhere inside it, the file command is only going to identify the containing filetype. Here are some examples of working with binary data in Python. Running the cat command on the embedded text file reveals THIS IS A HIDDEN FLAG.. CRC error in chunk pHYs (computed 38d82c82, expected 495224f0) Any advice/suggestion/help would be greatly appreciated. With the help of a hex editor we added the missing 0x0D byte, renamed the file and. ! Privacy Policy. Network traffic is stored and captured in a PCAP file (Packet capture), with a program like tcpdump or Wireshark (both based on libpcap). `89 50 4E 47 0D 0A 1A 0A` Many hex-editors also offer the ability to copy bytes and paste them as a new file, so you don't need to study the offsets. 00000000: 9050 4e47 0e1a 0a1b .PNG. (decimal) 137 80 78 71 13 10 26 10, (hexadecimal) 89 50 4e 47 0d 0a 1a 0a, (ASCII C notation) \211 P N G \r \n \032 \n. It also uses an identification heuristic, but with certainty percentages. And we got the final image : mystery: data Please Before going further with the challenge details, Id like to quickly summarize how a PNG file actually is. Which meant: why would you bruteforce everything? After using a tool such as pngcheck, if there are critical chunks with incorrect sizes defined, then this tool will automatically go through each critical chunk and fix their sizes for you. Learn why such statements are most of the time meaningless, understand the technical background, and find out which tool you should use as of today. Are you sure you want to create this branch? ctf Usually the goal here is to extract a file from a damaged archive, or find data embedded somewhere in an unused field (a common forensics challenge).