What’s Vulnerable › Vulnerabilities

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

• Severity: low (CVSS 2.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-10-20 · updated 2026-10-21
• Weakness: CWE-59

Description

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.

Affected products

• tox-dev filelock: from 3.32.6 before 4.2.1 — fixed in 4.2.1

How to fix

Upgrade to a fixed version: tox-dev filelock 4.2.1. Check the vendor advisory for mitigations.

References

• https://github.com/tox-dev/filelock/commit/e1e825b1992f69fb6b346dc395d5ae4893536c0a
• https://github.com/tox-dev/filelock/pull/835
• https://github.com/tox-dev/filelock/releases/tag/4.2.1
• https://github.com/tox-dev/filelock/security/advisories/GHSA-9j6q-wvj5-jgjg
• https://github.com/tox-dev/filelock/security/advisories/GHSA-9j6q-wvj5-jgjg

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