CVE-2026-112939: filelock is a platform-independent file lock for Python

Q: How do I fix CVE-2026-112939?

filelock: upgrade to 4.2.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-112939 being exploited?

CVE-2026-112939 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-112939 affect?

CVE-2026-112939 affects filelock. Severity is medium (CVSS 4.7). filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can trust a forged process identifier in a marker that an attacker can modify but cannot remove, allowing an authorized contender such as another

Q: How urgent is CVE-2026-112939?

Priority 22/100. Public exploit reference

Routine

MEDIUM 4.7UPGRADE

CVE-2026-112939 is a medium-severity flaw (CVSS 4.7) affecting filelock. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can trust a forged process identifier in a marker that an attacker can modify but cannot remove, allowing an authorized contender such as another process of the holder's account or root to act as a confused deputy, remove the live marker, and admit another holder. This issue is fixed in version 4.2.1.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	4.7 (Medium)
Attack vector	Local
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.1% (top 97%)
CISA exploited list	No
Weakness	CWE-345
Published	2026-10-20
Last modified	2026-10-21

Publisher (CNA): GitHub, Inc. · Vendor: tox-dev

Last updated 2026-10-21 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-10-20 15:17 UTCPublished CVE record published
2026-10-21 18:02 UTCUpdated Record last modified

tox-dev filelock UPGRADE

Affected: >= 3.22.0 and < 4.2.1

Fixed in: 4.2.1

Safe to downgrade to: a release before 3.22.0

1. Check installed version

pip show filelock

2. UPGRADE to 4.2.1

pip install --upgrade "filelock>=4.2.1"

3. If no update is available yet, DOWNGRADE to a release before 3.22.0

pip index versions filelock pip install "filelock<3.22.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-112939?

filelock: upgrade to 4.2.1. Exact commands for each OS are on this page.

Is CVE-2026-112939 being exploited?

CVE-2026-112939 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-112939 affect?

CVE-2026-112939 affects filelock. Severity is medium (CVSS 4.7). filelock is a platform-independent file lock for Python. From 3.22.0 until 4.2.1, SoftFileLock can trust a forged process identifier in a marker that an attacker can modify but cannot remove, allowing an authorized contender such as another

How urgent is CVE-2026-112939?

Priority 22/100. Public exploit reference

Software pages

Python vulnerabilities

Related CVEs

CVE-2026-112940 HIGH 7.1 UPGRADE filelock is a platform-independent file lock for Python
CVE-2026-112934 MEDIUM 6.1 UPGRADE filelock is a platform-independent file lock for Python
CVE-2026-112911 MEDIUM 6.3 UPGRADE filelock is a platform-independent file lock for Python
CVE-2026-112912 LOW 2.5 UPGRADE filelock is a platform-independent file lock for Python
CVE-2026-112914 MEDIUM 5.3 UPGRADE filelock is a platform-independent file lock for Python

References

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