What’s Vulnerable › Vulnerabilities

CVE-2025-11712: An OBJECT tag type attribute overrode browser behavior on web resources without a content-type

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-10-14 · updated 2026-10-23
• Weakness: CWE-116

Description

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; before 144.0 — fixed in 140.4.0, 144.0
• Mozilla Thunderbird: before 140.4.0; from 141.0 before 144.0 — fixed in 140.4.0, 144.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.4.0, 144.0; Mozilla Thunderbird 140.4.0, 144.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1979536
• https://www.mozilla.org/security/advisories/mfsa2025-81/
• https://www.mozilla.org/security/advisories/mfsa2025-83/
• https://www.mozilla.org/security/advisories/mfsa2025-84/
• https://www.mozilla.org/security/advisories/mfsa2025-85/
• https://lists.debian.org/debian-lts-announce/2025/10/msg00015.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00031.html

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