│ Category: Binary Exploitation
│ Difficulty: Medium
│ Points: 368
│ Author: Imattas aka Zemi
│ Flag: bbb{REDACTED}
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--[ Challenge Description ]--
│ Public challenge prompt was not recoverable from indexed sources.
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--[ Recon / Initial Analysis ]--
Challenge name and point value were recovered from official index snippets; full
handout was not archived.
The first pass is to avoid guessing from the bird-themed prompt and instead
build a small, repeatable workflow around the handout or service. For this file,
the public archive did not expose enough verified challenge material to claim a
completed solve transcript, so the writeup records the clean solve path I would
use once the handout is available.
-- bash --
$ mkdir -p work/{handout,notes,scripts}
$ file handout/* 2>/dev/null || true
$ strings -a handout/* 2>/dev/null | head -50
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--[ Vulnerability / Observation ]--
Unverified. A likely target area is mismatch between normalized paths and the
backing object store, or an unsafe parser for object metadata.
Model the virtual filesystem first, then audit path canonicalization, object
lifetime, and git-object parsing boundaries.
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--[ Exploitation / Solution ]--
:: Step 1 — Rebuild the challenge context
Keep the local environment close to the remote challenge. Save the original
handout, record hashes, and write every probe as a command or script so the path
can be repeated.
-- bash --
$ sha256sum handout/*
$ tree -a handout
:: Step 2 — Reduce the problem
1. Create a clean local repo/fixture set that mirrors the service expectations.
2. Exercise path edge cases: .., duplicate separators, symlinks, empty names,
and overlong entries.
3. Trace whether the service authorizes before or after canonicalization.
4. For native code, inspect allocations around tree/blob parsing.
5. Use the first primitive to read the flag object or corrupt control data.
:: Step 3 — Confirm the flag path
The final check is always local first: the script should either print bbb{...}
directly or produce one artifact where the flag is visible. Only after that
should the same payload or input be sent to the live challenge service.
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--[ Full Exploit Script ]--
-- python --
#!/usr/bin/env python3
from pathlib import PurePosixPath
CANDIDATES = [
'flag',
'/flag',
'../flag',
'..//flag',
'%2e%2e/flag',
'refs/heads/../../flag',
'objects/../flag',
]
def normalize(path: str) -> str:
return str(PurePosixPath('/', path))
def main():
for candidate in CANDIDATES:
print(f'{candidate:28} -> {normalize(candidate)}')
if __name__ == '__main__':
main()
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--[ Key Takeaways ]--
- Filesystem challenges often fail at normalization boundaries.
- Keep a corpus of path traversal and git object edge cases for quick coverage.
- Do not submit this generated file as an official qualifying writeup without
adding your own verified solve notes, command output, and final flag.