TI-2026-76858 Aliases CVE-2026-112935 GHSA-fq56-3cx3-fjxp

Race condition in filelock SoftFileLock admits two lock holders

MEDIUM 55CWE-367Published 2026-10-20 · Updated 2026-10-28

Key facts

Attack vector: Local
Privileges required: Low
User interaction: None
Attack complexity: High
Impact type: —
Confidentiality · integrity · availability: None · High · None
Fix status: Partial Red Hat: 15 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat.

Summary

filelock for Python, from 3.22.0 before 4.2.1, has a time-of-check time-of-use race condition (CWE-367) in SoftFileLock stale lock handling. A local attacker with low privileges can free its own marker after a stale read, so a live lock file is removed and two holders are admitted. A proof-of-concept exploit is linked in the references.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can break a stale marker after an attacker frees its own marker following the stale read, an honest contender creates a live successor on the reused inode, and the successor's modification time is not newer than the saved observation, causing the live marker to be removed and two holders to be admitted. This issue is fixed in version 4.2.1.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00132 2nd percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Partial filelock (tox-dev): 4.2.1filelock (PyPI): 4.2.1Red Hat: 15 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
tox-dev	filelock	3.22.0 to before 4.2.1	4.2.1	Patch available	CNA
—	filelock (PyPI)	3.22.0 to before 4.2.1	4.2.1	Patch available	GHSA-fq56-3cx3-fjxp

filelock Vendortox-dev Affected 3.22.0 to before 4.2.1 Fixed in 4.2.1 Patch available CNA
filelock (PyPI) Vendor— Affected 3.22.0 to before 4.2.1 Fixed in 4.2.1 Patch available GHSA-fq56-3cx3-fjxp

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:tox-dev:filelock::::::python::*	3.22.0 to before 4.2.1	Vulnerable	tox-dev

cpe:2.3:a:tox-dev:filelock:*:*:*:*:*:python:*:* Versions 3.22.0 to before 4.2.1 Vulnerable ·tox-dev

Remediation

Upgrade filelock to version 4.2.1, the fixed version in the PyPI package. Red Hat lists these products as affected with no fix available: Ansible Automation Orchestrator 2026 (none available), Exploit Intelligence (no fix planned), Lightspeed Core (none available), Lightspeed Services for Advanced Cluster Management (none available), OpenShift Lightspeed (none available) and other products.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Fix · CNA filelock (tox-dev) Fixed in 4.2.1
Fix · GHSA-fq56-3cx3-fjxp filelock (PyPI) Fixed in 4.2.1 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Ansible Automation Orchestrator 2026	Affected	No fix yet: Fix deferred
Exploit Intelligence	Affected	No fix planned: Out of support scope
Lightspeed Core	Affected	No fix yet: Fix deferred
Lightspeed Services for Advanced Cluster Management	Affected	No fix yet: Fix deferred
OpenShift Lightspeed	Affected	No fix yet: Fix deferred
Pen Drive Powered by Red Hat Lightspeed	Affected	No fix yet: Fix deferred
Red Hat AI Inference Server	Affected	No fix yet: Fix deferred
Red Hat Ansible Automation Platform 2	Affected	No fix yet: Fix deferred
Red Hat Ansible Automation Platform Ansible Core 2	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux AI (RHEL AI) 3	Affected	No fix yet: Fix deferred
Red Hat Lightspeed Services for OCP	Affected	No fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)	Affected	No fix yet: Fix deferred
Red Hat OpenShift Container Platform 4	Affected	No fix yet: Fix deferred
Red Hat OpenShift Dev Spaces	Affected	No fix yet: Fix deferred
Red Hat Satellite 6	Affected	No fix yet: Fix deferred

Timeline

2026-10-20 Threatist record created from CVE-2026-112935
2026-10-21 Affected versions changed · Red Hat
2026-10-21 CVSS score added · Red Hat
2026-10-28 CISA SSVC decision points changed
2026-10-28 Priority changed: LOW → MEDIUM
2026-10-28 Alias added: GHSA-fq56-3cx3-fjxp
2026-10-28 Fix available: PyPI/[email protected] · GHSA-fq56-3cx3-fjxp
2026-10-28 CVSS score added · GHSA-fq56-3cx3-fjxp
2026-10-28 Weakness changed · GHSA-fq56-3cx3-fjxp
2026-10-28 6 new references · GHSA-fq56-3cx3-fjxp

References

Exploit 1

https://github.com/tox-dev/filelock/security/advisories/GHSA-fq56-3cx3-fjxp

Patch 2

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2026-112935

Other 2

TI-2026-76862 Symlink race in filelock ReadWriteLock lets attackers overwrite files CVSS 3.1HIGH 7.1
TI-2026-76853 filelock soft locks adopt directories created by other local users CVSS 3.1MEDIUM 6.3
TI-2026-76859 Symlink following in filelock ReadWriteLock redirects SQLite database CVSS 3.1MEDIUM 6.1
TI-2026-76857 Unsafe holder record refresh in filelock SoftReadWriteLock CVSS 3.1MEDIUM 6.1
TI-2026-76852 filelock UnixFileLock truncates files placed on the lock path CVSS 3.1MEDIUM 6.1
TI-2026-76856 Crafted lock database makes filelock ReadWriteLock acquisitions hang CVSS 3.1MEDIUM 5.5

See all 14 →

Sources

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