Completed the Gavel (Medium) machine on Hack The Box. The initial foothold came from an exposed .git directory that leaked the application’s source code and bcrypt password hashes. After cracking the credentials with John the Ripper, I gained access and achieved a reverse shell through command injection in the admin rule field. Reusing the cracked credentials allowed privilege escalation to the application user and retrieval of the user flag.

Root access was obtained by abusing the gavel-util submission feature, which executed YAML rule fields using PHP system(). By overwriting the custom php.ini to remove restrictions and creating a SUID Bash binary, it was possible to spawn a root shell and capture the final flag.

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Learn MoreHack The Box: Gavel Machine Walkthrough – Medium Difficulity