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.
Fix
Patch, vendor advisory and mitigation references on NVD 4
- https://www.mozilla.org/security/advisories/mfsa2025-81/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-83/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-84/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-85/ Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 6.1 · mozillaNVD modified 2026-10-18 21:10
Affected (CPE criteria) 3
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
References 7
- https://bugzilla.mozilla.org/show_bug.cgi?id=1979536 Issue Tracking, Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2025-81/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-83/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-84/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2025-85/ Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2025/10/msg00015.html
- https://lists.debian.org/debian-lts-announce/2025/10/msg00031.html