CVE-2025-1942: Mozilla Firefox

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

When String.toUpperCase() caused a string to get longer it was possible for uninitialized memory to be incorporated into the result string. This vulnerability was fixed in Firefox 136 and Thunderbird 136.

Affected products

• Mozilla Firefox: before 136.0 (fixed in 136.0)
• Mozilla Thunderbird: before 136.0 (fixed in 136.0)

Published 2025-03-04. Last modified 2026-10-05.