CVE-2025-1009: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 1.2% chance of exploitation in the next 30 days.

An attacker could have caused a use-after-free via crafted XSLT data, leading to a potentially exploitable crash. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

Affected products

• Mozilla Firefox: before 115.20.0 (fixed in 115.20.0); before 135.0 (fixed in 135.0); from 128.1.0, before 128.7.0 (fixed in 128.7.0)
• Mozilla Thunderbird: from 128.0.1, before 128.7.0 (fixed in 128.7.0); from 131.0, before 135.0 (fixed in 135.0)

Published 2025-02-04. Last modified 2026-10-05.