webhard

YouTroopers

alfactf

Task: Crowdfunding service for purchasing items, router costs 333 with user balance always 0. Solution: JWT token reuse after rename creates ghost participants, integer division truncation (int(333/334)=0) allows free purchase.

$ ls tags/ techniques/

toctou fastapi authentication_bypass python jwt_token_reuse business_logic integer_division file_based_storage crowdfunding

JWT token reuse after renameInteger division truncation (int(333/334) = 0)TOCTOU in user existence checkGhost participant creation

Analysis

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

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