CVE-2025-0243: Mozilla Firefox

Medium severity, CVSS 5.1. EPSS: 0.3% chance of exploitation in the next 30 days.

Memory safety bugs present in Firefox 133, Thunderbird 133, Firefox ESR 128.5, and Thunderbird 128.5. 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 134, Firefox ESR 128.6, Thunderbird 134, and Thunderbird 128.6.

Affected products

• Mozilla Firefox: before 128.6.0 (fixed in 128.6.0); before 133.0 (fixed in 133.0)
• Mozilla Thunderbird: before 128.6.0 (fixed in 128.6.0); from 129.0, before 134.0 (fixed in 134.0)

Published 2025-01-07. Last modified 2026-10-05.