CVE-2025-11712
📋 TL;DR
This vulnerability allows malicious web pages to bypass browser security controls using OBJECT tags when servers don't provide proper content-type headers. Attackers could potentially execute cross-site scripting (XSS) attacks against vulnerable websites. Affects Firefox, Firefox ESR, and Thunderbird users running outdated versions.
💻 Affected Systems
- Firefox
- Firefox ESR
- Thunderbird
📦 What is this software?
Firefox by Mozilla
Firefox by Mozilla
Thunderbird by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Successful XSS attacks leading to session hijacking, credential theft, or malware delivery to users visiting compromised sites.
Likely Case
Limited XSS exploitation on websites that improperly serve files without content-type headers, potentially affecting user sessions.
If Mitigated
No impact if browsers are updated or websites properly set content-type headers for all resources.
🎯 Exploit Status
Exploitation requires specific conditions: vulnerable browser + website serving files without content-type headers + malicious page using OBJECT tag manipulation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 144+, Firefox ESR 140.4+, Thunderbird 144+, Thunderbird 140.4+
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2025-81/
Restart Required: No
Instructions:
1. Open browser/application. 2. Go to Settings/Preferences. 3. Navigate to About/Updates section. 4. Allow automatic update or manually check for updates. 5. Restart if prompted.
🔧 Temporary Workarounds
Disable JavaScript for OBJECT tags
allConfigure browser to block JavaScript execution via OBJECT tags
Content-Type Header Enforcement
allEnsure all web servers properly set content-type headers for served files
🧯 If You Can't Patch
- Use alternative browsers that are not affected by this vulnerability
- Implement web application firewalls (WAF) to detect and block malicious OBJECT tag usage
🔍 How to Verify
Check if Vulnerable:
Check browser version in About section and compare against affected versionsCheck Version:
Browser-specific: Firefox/Thunderbird: about:support or Help > AboutVerify Fix Applied:
Confirm browser version is equal to or greater than patched versions: Firefox 144+, Firefox ESR 140.4+, Thunderbird 144+, Thunderbird 140.4+📡 Detection & Monitoring
Log Indicators:
- Unusual OBJECT tag usage in web server logs
- Multiple requests to same resource without content-type headers
Network Indicators:
- HTTP responses missing content-type headers
- Suspicious OBJECT tag parameters in web traffic
SIEM Query:
web.url CONTAINS "<OBJECT" AND web.response.content_type IS NULL🔗 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
