CVE-2025-5269: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 0.5% chance of exploitation in the next 30 days.

Memory safety bug present in Firefox ESR 128.10, and Thunderbird 128.10. This bug showed evidence of memory corruption and we presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox ESR 128.11 and Thunderbird 128.11.

Affected products

• Mozilla Firefox: before 128.11.0 (fixed in 128.11.0)
• Mozilla Thunderbird: before 128.11.0 (fixed in 128.11.0)

Published 2025-05-27. Last modified 2026-10-05.