# CVE-2026-112914: filelock SoftFileLock symlink attack via stale marker

Source: https://junglewise.ai/threats/cve-2026-112914-filelock-is-a-platform-independent-file-lock-for-python-from-4-1  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-112914 · Severity: medium · CVSS 5.3 · Published 2026-10-20

filelock is a Python library that implements cross-platform file locking for coordinating access to shared resources. A vulnerability in versions 4.1.0 through 4.2.1 allows a local attacker with rename permissions to exploit a race condition by swapping a moved lock marker with a symbolic link, potentially forcing the lock holder to create hard links into the lock directory. This could lead to privilege escalation or file corruption on systems where the attacker and lock holder are distinct users.

Technologies: [filelock (PyPI)](https://junglewise.ai/threats/technologies/filelock), [Tox-Dev Filelock](https://junglewise.ai/threats/technologies/tox-dev-filelock). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi), [Tox-Dev](https://junglewise.ai/threats/vendors/tox-dev).

## Quick answers

**Is CVE-2026-112914 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-112914 being exploited in the wild.

**How severe is CVE-2026-112914?** Medium severity, with a CVSS score of 5.3, published 20 October 2026.

**Which products and versions are affected?** filelock (PyPI) >= 4.1.0, <= 4.2.0, ECOSYSTEM:introduced=4.1.0,fixed=4.2.1; Tox-Dev Filelock 4.1.0 to 4.2.1.

**Is there a fix for CVE-2026-112914?** Yes. filelock (PyPI): upgrade to 4.2.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-112914 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-112914?** Check whether you run filelock (PyPI) or Tox-Dev Filelock at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- filelock (PyPI): upgrade to 4.2.1 or later

  ```sh
  pip install "filelock>=4.2.1"
  ```


## Technical details

SoftFileLock implementations fail to prevent symlink attacks when restoring a stale lock marker that was temporarily moved aside. An attacker with local filesystem access and rename permissions in the lock directory can replace the moved marker with a symlink pointing to a same-filesystem target, which the lock user will follow and hard-link. The vulnerability is a time-of-check-time-of-use (TOCTOU) race condition between moving the marker and checking it.

## Affected products

- tox-dev filelock 4.1.0 to 4.2.1

## Identifiers

- CVE-2026-112914
- GHSA-crv4-6mhj-j5jh

## Timeline

- 2026-10-20: disclosed
- 2026-10-17: patched

## References

- [https://github.com/tox-dev/filelock/commit/740ff666b62a88496c8d7394e4e6230605e4d62b](https://github.com/tox-dev/filelock/commit/740ff666b62a88496c8d7394e4e6230605e4d62b)
- [https://github.com/tox-dev/filelock/pull/843](https://github.com/tox-dev/filelock/pull/843)

## Related threats

- [filelock StrictSoftFileLock symlink race privilege escalation](https://junglewise.ai/threats/cve-2026-112938-filelock-strictsoftfilelock-follows-a-symbolic-link-swapped-in)
- [filelock: ReadWriteLock on Windows acts on SQLite side files another local user places beside its database](https://junglewise.ai/threats/cve-2026-112913-filelock-readwritelock-on-windows-acts-on-sqlite-side-files)
- [filelock WindowsFileLock mode parameter permission enforcement failure](https://junglewise.ai/threats/cve-2026-112910-filelock-windowsfilelock-ignores-mode-a-0o600-lock-file-and-the)
- [filelock StrictSoftFileLock directory permission bypass](https://junglewise.ai/threats/cve-2026-112908-filelock-strictsoftfilelock-creates-its-claim-directories)
- [filelock: On Windows an oplock on a soft lock's marker holds SoftFileLock.acquire() past its timeout and blocks the stale break](https://junglewise.ai/threats/cve-2026-112907-filelock-on-windows-an-oplock-on-a-soft-lock-s-marker-holds)