CVE-2025-11712: Mozilla Firefox

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

A malicious page could have used the type attribute of an OBJECT tag to override the default browser behavior when encountering a web resource served without a content-type. This could have contributed to an XSS on a site that unsafely serves files without a content-type header. This vulnerability was fixed in Firefox 144, Firefox ESR 140.4, Thunderbird 144, and Thunderbird 140.4.

Affected products

• Mozilla Firefox: before 140.4.0 (fixed in 140.4.0); before 144.0 (fixed in 144.0)
• Mozilla Thunderbird: before 140.4.0 (fixed in 140.4.0); from 141.0, before 144.0 (fixed in 144.0)

Published 2025-10-14. Last modified 2026-06-17.