Mojo-Vault: Integrity Bypass

Mojo-Vault presented itself as a hardened Bash script protected by an aggressive MD5 self-integrity mechanism. The script would hash itself upon execution; if a single byte was altered, it would immediately abort. However, close inspection of the bash logic revealed a critical architectural flaw: a Time-of-Check to Time-of-Use (TOCTOU) vulnerability.

During execution, the vault temporarily extracted vital dependency scripts to the /tmp directory before securely wiping them milliseconds later. I realized I could beat the cleanup routine by weaponizing a race condition.

I crafted a malicious bash loop using a named pipe (mkfifo) to intentionally stall the vault's input stream. While the vault hung waiting for input, the temporary files—including a highly sensitive boot.py—were sitting fully exposed in the /tmp directory. A secondary script snatched copies of the files before the vault resumed execution. Analyzing boot.py provided the master PIN, which, when base64-decoded, granted total system compromise.

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Key Takeaways

• Integrity checks are useless if the runtime artifacts are not securely sandboxed. TOCTOU vulnerabilities in /tmp extractions are highly lethal.
• Named pipes (FIFOs) can be weaponized to indefinitely pause blocking scripts, breaking critical cleanup timing loops.

Beyond the challenge

Consider an installer or wrapper that decrypts a helper into a temporary directory, runs it, then deletes it. A copy may be obtainable while the helper exists, even if the launcher later reports successful cleanup. This is the practical connection to examining runtime artifacts here.

Check temporary-file permissions, lifetime and contents as well as the wrapper's integrity check. Cleanup reduces how long data remains; it does not erase a copy already obtained. A local file exposure also needs an access model: the result does not automatically mean that every user or remote attacker can read the temporary file.

Keep learning

• GDB manual: learn the process-control concepts behind pausing execution and inspecting runtime state.