CVE-2026-14534 PUBLISHED

Fickling check_safety() bypass via unlisted standard library modules (_posixsubprocess, site, atexit)

Assigner: BombadilSystems
Reserved: 03.07.2026 Published: 04.07.2026 Updated: 04.07.2026

Trail of Bits fickling versions up to and including 0.1.10 do not include the Python standard library modules _posixsubprocess, site, and atexit in the UNSAFE_IMPORTS denylist (fickle.py). Because these modules are absent from the denylist, fickling's check_safety() function returns LIKELY_SAFE with zero findings for pickle payloads that invoke dangerous functions including _posixsubprocess.fork_exec (C-level process spawner capable of executing arbitrary binaries), site.execsitecustomize (executes arbitrary site customization code), and atexit._run_exitfuncs (triggers all registered exit handler callbacks). The fickling.load() API chains check_safety() into pickle.loads() as an explicit security gate; a LIKELY_SAFE verdict causes the payload to be deserialized and executed. This shares the same root cause as CVE-2026-22607 (cProfile), CVE-2025-67748 (pty), and CVE-2025-67747 (marshal/types). OvertlyBadEvals does not flag these modules because they are standard library imports. UnsafeImports does not flag them because they are not in the denylist. The UnusedVariables heuristic is defeated by the SETITEMS opcode pattern.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS Score: 8.8

Product Status

Vendor trailofbits
Product fickling
Versions Default: unaffected
  • affected from 0 to 0.1.10 (incl.)
  • Version 0.1.11 is unaffected

Credits

  • Christopher Aziz (Bombadil Systems LLC) finder

References

Problem Types

  • CWE-184 Incomplete List of Disallowed Inputs CWE
  • CWE-502 Deserialization of Untrusted Data CWE

Impacts

  • An attacker can craft a malicious pickle file that invokes _posixsubprocess.fork_exec to spawn arbitrary processes. When a victim's ML pipeline passes this file through fickling.load(), fickling classifies it as LIKELY_SAFE and deserializes it, executing attacker-controlled code with the privileges of the victim process.