webhard

Sanchess

ASIS CTF

Task: read flag.txt from a Flask chess game with eval() injection filtered against parentheses, quotes, and underscores. Solution: use chr() to build strings without quotes, access builtins via getattr(__builtins__, chr-encoded name), and exfiltrate via binary search on the conditional move oracle.

$ ls tags/ techniques/

flask filter_bypass werkzeug binary_search python_eval chr_encoding blind_exfiltration chess_game api endpoint discovery json

eval_injectionfilter_bypass_with_chrgetattr_builtin_accessbinary_search_exfiltrationconditional_oracleendpoint_enumerationsource_code_analysis

Analysis

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$ python3 exploit.py --target 192.168.1.1 --port 8080
[*] Connecting to target...
[+] Shell obtained!

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