# CVE-2026-112912: filelock: Symlink swap during SoftFileLock's writability check leaks whether a path exists and is writable by the lock taker

Source: https://junglewise.ai/threats/cve-2026-112912-filelock-is-a-platform-independent-file-lock-for-python-from-3  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-112912 · Severity: low · CVSS 3.1 · Published 2026-10-20

filelock is a platform-independent file lock for Python. From 3.32.6 until 4.2.1, SoftFileLock can follow a swapped symbolic link during the conditional os.access writability check for a node without its owner-write bit, allowing another local user on a platform and directory configuration that follows the link to infer whether a chosen path exists and is writable from the observable acquisition result. This issue is fixed in version 4.2.1.

Technologies: [filelock (PyPI)](https://junglewise.ai/threats/technologies/filelock). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-112912 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-112912 being exploited in the wild.

**How severe is CVE-2026-112912?** Low severity, with a CVSS score of 3.1, published 20 October 2026.

**Which products and versions are affected?** filelock (PyPI) >= 3.32.6, <= 4.2.0, ECOSYSTEM:introduced=3.32.6,fixed=4.2.1.

**Is there a fix for CVE-2026-112912?** 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.

**Am I affected by CVE-2026-112912?** Check whether you run filelock (PyPI) 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"
  ```


## Affected products

- filelock (PyPI) >= 3.32.6, <= 4.2.0, ECOSYSTEM:introduced=3.32.6,fixed=4.2.1

## Identifiers

- CVE-2026-112912
- GHSA-9j6q-wvj5-jgjg

## 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)