Flatpack-522.rar -

The archive is deliberately obfuscated: it contains a password‑protected inner RAR, a steganographically‑hidden image, and a small custom‑packed executable that must be run in a controlled environment. $ file flatpack-522.rar flatpack-522.rar: RAR archive data, version 5, created Tue Sep 5 13:42:10 2023, encrypted

DECIMAL HEX DESCRIPTION 0 0x0 PNG image, 256 x 256, 8-bit/color RGBA, non-interlaced Extract the PNG:

$ binwalk mystery.bin Output:

The secret lies within the binary. So the PNG is just a hint, not the flag itself. 6.1 File Type $ file mystery.bin mystery.bin: data Run binwalk to look for embedded files: flatpack-522.rar

The goal of the challenge is to retrieve the hidden flag that the creator has concealed inside the RAR file. The write‑up is organized into the typical CTF sections: , exploitation / analysis , extraction , and flag retrieval . 1. Overview & Goal | Item | Description | |------|-------------| | Challenge name | FlatPack‑522 | | File | flatpack-522.rar (≈ 2 MiB) | | Category | Forensics / Reverse Engineering | | Typical points | 200‑300 (depends on the event) | | Goal | Extract the hidden flag (format: HTB... or FLAG... ) from the archive. |

$ steghide extract -sf cover.png -p "" -xf hidden.txt (If steghide asks for a password, just press Enter – it’s not password protected.)

$ display cover.png Nothing obvious appears. However, the challenge name “FlatPack” hints at “flat” data (i.e., a flat image with hidden data). Use zsteg (a popular stego tool) to search for hidden data: The archive is deliberately obfuscated: it contains a

#!/usr/bin/env bash set -e

Good luck, and happy hunting!

Cannot open encrypted file. Use -p option to specify a password. Thus we need the password. 3.1 Brute‑Force / Dictionary Attempts A quick dictionary attack with common passwords (e.g., password , 12345 , admin ) fails. The creator hints in the challenge description: “The key is hidden inside the name of the pack itself.” The file name flatpack‑522 suggests the password may be related to the number 522 . Overview & Goal | Item | Description |

$ zsteg -a cover.png Output shows:

Try the following candidates:

$ zbarimg _mystery.bin.extracted/00000000.png QR-Code:HTBfl4t_p4ck_5c4nn3r_2023 That is the flag. Below is a one‑liner script that reproduces the entire process automatically. It assumes you have unrar , zsteg , binwalk , and zbarimg installed.

# 4. Unpack the binary blob binwalk -e mystery.bin > /dev/null

# 2. Extract inner archive (no password) unrar x inner.rar