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

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Summary

CVECVE-2026-14534
StatePUBLISHED
AssignerBombadilSystems
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-04 14:16:28 UTC
Updated2026-07-04 14:16:28 UTC
DescriptionTrail 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.

Risk And Classification

Primary CVSS: v3.1 8.8 HIGH from aa17e1a1-c329-4d6e-a1ed-8d0188aea082

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

Problem Types: CWE-184 | CWE-502 | CWE-184 CWE-184 Incomplete List of Disallowed Inputs | CWE-502 CWE-502 Deserialization of Untrusted Data

VersionSourceTypeScoreSeverityVector
3.1aa17e1a1-c329-4d6e-a1ed-8d0188aea082Secondary8.8HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
3.1CNACVSS8.8HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Trailofbits Fickling affected 0.1.10 custom Not specified
CNA Trailofbits Fickling unaffected 0.1.11 custom Not specified

References

ReferenceSourceLinkTags
github.com/trailofbits/fickling/security/advisories/GHSA-m6fh-58r7-x697 aa17e1a1-c329-4d6e-a1ed-8d0188aea082 github.com
github.com/trailofbits/fickling/pull/272 aa17e1a1-c329-4d6e-a1ed-8d0188aea082 github.com
github.com/trailofbits/fickling/commit/e8408615b63adf034f891f653692ab9b5... aa17e1a1-c329-4d6e-a1ed-8d0188aea082 github.com
github.com/trailofbits/fickling/releases/tag/v0.1.11 aa17e1a1-c329-4d6e-a1ed-8d0188aea082 github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Christopher Aziz (Bombadil Systems LLC) (en)

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