CVE-2025-5272: Mozilla Firefox

High severity, CVSS 7.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Memory safety bugs present in Firefox 138 and Thunderbird 138. 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 139 and Thunderbird 139.

Affected products

• Mozilla Firefox: before 139.0 (fixed in 139.0)
• Mozilla Thunderbird: before 139.0 (fixed in 139.0)

Published 2025-05-27. Last modified 2026-09-30.