Picklescan is vulnerable to RCE through missing detection when calling built-in python operator.methodcaller

Summary

### Summary Picklescan uses `operator.methodcaller`, which is a built-in python library function to execute remote pickle files. ### Details The attack payload executes in the following steps: - First, the attacker crafts the payload by calling the `operator.methodcaller` function in method `reduce`. - Then, when the victim checks whether the pickle file is safe using the Picklescan library and this library doesn't detect any dangerous functions, they decide to use pickle.load() on this malicious pickle file, thus leading to remote code execution. ### PoC ``` import pickle import pickletools opcode1 = b'''cbuiltins __import__ (Vos tRp0 0coperator methodcaller (Vsystem Vecho "pwned by operator.methodcaller" tR(g0 tR.''' pickletools.dis(opcode1) pickle.loads(opcode1) ``` This PoC can't be easily created by pickle.dumps, therefore it was manually built. ### Impact Any organization or individual relying on picklescan to detect malicious pickle files inside PyTorch models. Attackers can embed malicious code in pickle file that remains undetected but executes when the pickle file is loaded. Attackers can distribute infected pickle files across ML models, APIs, or saved Python objects. ### Report by Pinji Chen ([email protected]) from the NISL lab (https://netsec.ccert.edu.cn/about) at Tsinghua University, Guanheng Liu ([email protected]).