CVE-2026-100779: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.3% chance of exploitation in the next 30 days.

Use-after-free in the XSLT component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Affected products

• Mozilla Firefox: before 157.0.0 (fixed in 157.0.0); from 115.1.0, before 115.42.0 (fixed in 115.42.0); from 140.0, before 140.17.0 (fixed in 140.17.0); from 153.0, before 153.4.0 (fixed in 153.4.0)
• Mozilla Thunderbird: before 157.0 (fixed in 157.0); from 140.0, before 140.17.0 (fixed in 140.17.0); from 153.0, before 153.4.0 (fixed in 153.4.0)

Published 2026-09-29. Last modified 2026-10-05.