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Medium, CVSS 4.7amended

filelock: SoftFileLock stale-lock break removes a live lock file on a reused inode number and admits two holders

CVE-2026-112935GHSA-fq56-3cx3-fjxp

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (filelock 4.2.1), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI filelock

    Affected
    >= 3.22.0, < 4.2.1
    Fixed in
    4.2.1

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
4.7 · CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
EPSS
  • CVE-2026-112935: 0.13% estimated exploitation activity in the next 30 days; percentile 2.79 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

The stale-lock break shared by `SoftFileLock`, `MarkerSoftFileLock` and `SoftFileLease` (and their async variants, and a `FileLock` that has fallen back to a soft lock on `ENOSYS`, the "not implemented" error) recognises the marker it judged stale by two values. The marker is the lock file at ` `, whose presence says a process holds the lock. The values are its inode number (the kernel's identity for a file, independent of its name) and its modification time (mtime) not being newer. The check runs after the contender has already closed the marker, so nothing keeps the inode allocated. On a filesystem that hands a freed inode number straight to the next file (ext4, xfs, overlayfs on them) the next holder's marker can carry that number. A contender still between its read and its break then renames and unlinks the live marker. Another local user (the other user below) who can create files in the lock's directory, a sticky `/tmp` included (the sticky bit is a directory flag that lets…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-fq56-3cx3-fjxp

  2. Revision 1 · created ·

    Published from ghsa record GHSA-fq56-3cx3-fjxp

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-112935

Advisory: filelock: SoftFileLock stale-lock break removes a live lock file on a reused inode number and admits two holders
IDs: CVE-2026-112935, GHSA-fq56-3cx3-fjxp
Record: https://patchnext.com/advisories/cve-2026-112935 (revision 2, source checked 29 Oct 2026, 06:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: filelock 4.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI filelock: affected >= 3.22.0, < 4.2.1; fixed in 4.2.1

## Suggested inspection (read-only)
- `python -m pip show filelock`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on filelock.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-fq56-3cx3-fjxp (GitHub-reviewed advisory GHSA-fq56-3cx3-fjxp lists affected ranges: PyPI filelock >=3.22.0 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-fq56-3cx3-fjxp (OSV record GHSA-fq56-3cx3-fjxp lists affected ranges: PyPI filelock >=3.22.0 <4.2.1 (fixed))

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