CVE-2025-8037: Mozilla Firefox

Critical severity, CVSS 9.1. EPSS: 0.2% chance of exploitation in the next 30 days.

Setting a nameless cookie with an equals sign in the value shadowed other cookies. Even if the nameless cookie was set over HTTP and the shadowed cookie included the `Secure` attribute. This vulnerability was fixed in Firefox 141, Firefox ESR 140.1, Thunderbird 141, and Thunderbird 140.1.

Affected products

• Mozilla Firefox: before 140.1 (fixed in 140.1); before 141.0 (fixed in 141.0)
• Mozilla Thunderbird: before 140.1 (fixed in 140.1); before 141.0 (fixed in 141.0)

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