CVE-2025-8027: Mozilla Firefox

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

On 64-bit platforms IonMonkey-JIT only wrote 32 bits of the 64-bit return value space on the stack. Baseline-JIT, however, read the entire 64 bits. This vulnerability was fixed in Firefox 141, Firefox ESR 115.26, Firefox ESR 128.13, Firefox ESR 140.1, Thunderbird 141, Thunderbird 128.13, and Thunderbird 140.1.

Affected products

• Mozilla Firefox: before 115.26.0 (fixed in 115.26.0); before 141.0 (fixed in 141.0); from 128.0, before 128.13.0 (fixed in 128.13.0); from 140.0, before 140.1.0 (fixed in 140.1.0)
• Mozilla Thunderbird: before 128.13.0 (fixed in 128.13.0); before 141.0 (fixed in 141.0); from 140.0, before 140.1.0 (fixed in 140.1.0)

Published 2025-07-22. Last modified 2026-10-05.