CVE-2025-9187: Mozilla Firefox

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

Memory safety bugs present in Firefox 141 and Thunderbird 141. 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 142 and Thunderbird 142.

Affected products

• Mozilla Firefox: before 142.0 (fixed in 142.0)
• Mozilla Thunderbird: before 142.0 (fixed in 142.0)

Published 2025-08-19. Last modified 2026-09-30.