A critical vulnerability has been discovered in the Action Pack Page Caching component of Ubuntu, affecting versions 20.04, 18.04, and 16.04. This flaw allows remote attackers to write arbitrary files on the web server and potentially execute arbitrary code.

The vulnerability, identified as USN-9058-1, arises from improper handling of request paths when writing cached pages. Due to its potential for exploitation, it has been classified as critical.

Patches were made available immediately following the disclosure of the vulnerability on November 11, 2026. Affected users are advised to prioritize applying the patches provided by Ubuntu Pro.

Ubuntu Pro has provided the necessary patches, and affected users are urged to prioritize their application.