CVE-2025-1020: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 0.5% chance of exploitation in the next 30 days.

Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 135 and Thunderbird 135.

Affected products

• Mozilla Firefox: before 135.0 (fixed in 135.0)
• Mozilla Thunderbird: from 131.0, before 135.0 (fixed in 135.0)

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