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Medium, CVSS 6.1amended

filelock: SoftReadWriteLock holder refresh writes through a hard link and hangs on a named pipe that another local user renames over its record

CVE-2026-112934GHSA-fj95-fr6c-h845

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
    >= 4.0.0, < 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
6.1 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
EPSS
  • CVE-2026-112934: 0.23% estimated exploitation activity in the next 30 days; percentile 14.23 (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.

`SoftReadWriteLock` (and `AsyncSoftReadWriteLock`, which wraps one) refreshes its holder record (the file under ` .rw/holders/` that says a process holds or wants the lock) on every poll of a waiting acquire and on every heartbeat (the periodic refresh a holder runs to keep its record fresh). It does so by reopening ` .rw/holders/ ` by name with a plain blocking `O_WRONLY | O_NOFOLLOW` open and writing at offset 0, without checking what it opened. `O_NOFOLLOW` makes the open fail only when the final name is a symbolic link (a file that redirects to another path). A different local user (the other user below) who owns the lock's `.rw` tree reads the token of the user running the lock (the lock user below) from the `holders/` listing and renames another node over the record. The other user owns the tree because it created it first in a sticky directory such as `/tmp` (the sticky bit is a directory flag that lets only a file's owner rename or remove it), or because it can write a lock…

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

    Amended from osv record GHSA-fj95-fr6c-h845

  2. Revision 1 · created ·

    Published from ghsa record GHSA-fj95-fr6c-h845

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-2026-112934

Advisory: filelock: SoftReadWriteLock holder refresh writes through a hard link and hangs on a named pipe that another local user renames over its record
IDs: CVE-2026-112934, GHSA-fj95-fr6c-h845
Record: https://patchnext.com/advisories/cve-2026-112934 (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 6.1)
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 >= 4.0.0, < 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-fj95-fr6c-h845 (GitHub-reviewed advisory GHSA-fj95-fr6c-h845 lists affected ranges: PyPI filelock >=4.0.0 <=4.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-fj95-fr6c-h845 (OSV record GHSA-fj95-fr6c-h845 lists affected ranges: PyPI filelock >=4.0.0 <4.2.1 (fixed))

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