Mozilla Firefox's update mechanism allowed a medium-integrity user process to interfere with the SYSTEM-level updater by manipulating the file-locking behavior. By injecting code into the user-privileged process, an attacker could bypass intended access controls, allowing SYSTEM-level file operations on paths controlled by a non-privileged user and enabling privilege escalation. This vulnerability affects Firefox < 138, Firefox ESR < 128.10, Firefox ESR < 115.23, Thunderbird < 138, and Thunderbird ESR < 128.10.

https://bugzilla.mozilla.org/show_bug.cgi?id=1917536

https://www.mozilla.org/security/advisories/mfsa2025-28/

https://www.mozilla.org/security/advisories/mfsa2025-29/

https://www.mozilla.org/security/advisories/mfsa2025-30/

https://www.mozilla.org/security/advisories/mfsa2025-31/

https://www.mozilla.org/security/advisories/mfsa2025-32/