tox-dev filelock up to 3.20.2 on Python File Creation _acquire link following

Summaryinfo

A vulnerability has been found in tox-dev filelock up to 3.20.2 on Python and classified as critical. Affected by this issue is the function _acquire of the component File Creation Handler. The manipulation leads to link following. This vulnerability is referenced as CVE-2026-22701. The attack can only be performed from a local environment. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in tox-dev filelock up to 3.20.2 on Python and classified as problematic. This issue affects the function _acquire of the component File Creation Handler. The manipulation with an unknown input leads to a link following vulnerability. Using CWE to declare the problem leads to CWE-59. The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource. Impacted is integrity, and availability. The summary by CVE is:

filelock is a platform-independent file lock for Python. Prior to version 3.20.3, a TOCTOU race condition vulnerability exists in the SoftFileLock implementation of the filelock package. An attacker with local filesystem access and permission to create symlinks can exploit a race condition between the permission validation and file creation to cause lock operations to fail or behave unexpectedly. The vulnerability occurs in the _acquire() method between raise_on_not_writable_file() (permission check) and os.open() (file creation). During this race window, an attacker can create a symlink at the lock file path, potentially causing the lock to operate on an unintended target file or leading to denial of service. This issue has been patched in version 3.20.3.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-22701 since 01/08/2026. The exploitation is known to be difficult. An attack has to be approached locally. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 282557 (Linux Distros Unpatched Vulnerability : CVE-2026-22701), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.20.3 eliminates this vulnerability. Applying the patch 255ed068bc85d1ef406e50a135e1459170dd1bf0 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (282557) and EUVD (EUVD-2026-1870). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• tox-dev

Name

• filelock

Version

• 3.20.0
• 3.20.1
• 3.20.2

License

• open-source

Website

• Product: https://github.com/tox-dev/filelock/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion