CVE-2025-2817: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.7% chance of exploitation in the next 30 days.

Thunderbird'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 was fixed in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10.

Affected products

• Mozilla Firefox: before 115.23.0 (fixed in 115.23.0); before 138.0 (fixed in 138.0); from 116.0, before 128.10.0 (fixed in 128.10.0)
• Mozilla Thunderbird: before 128.10.0 (fixed in 128.10.0); from 129.0, before 138.0 (fixed in 138.0)

Published 2025-04-29. Last modified 2026-10-05.