Known exploited vulnerability · CISA KEV

CVE-2010-3765: Mozilla Multiple Products Remote Code Execution Vulnerability

Mozilla Firefox, SeaMonkey, and Thunderbird contain an unspecified vulnerability when JavaScript is enabled. This allows remote attackers to execute arbitrary code via vectors related to nsCSSFrameConstructor::ContentAppended, the appendChild method, incorrect index tracking, and the creation of multiple frames, which triggers memory corruption.

CVE-2010-3765

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2025-10-06: attackers are using it right now.

CISA KEV: Listed; Added 2025-10-06 · federal fix-by 2025-10-27
EPSS (30 days): 83%; Higher than 99.7% of CVEs · 2026-11-01
CVSS v3.1: 9.8 Critical; CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

What CISA says

Mozilla Multiple Products Remote Code Execution Vulnerability

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

NVD description · published 2010-10-28

Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x before 2.0.10, when JavaScript is enabled, allows remote attackers to execute arbitrary code via vectors related to nsCSSFrameConstructor::ContentAppended, the appendChild method, incorrect index tracking, and the creation of multiple frames, which triggers memory corruption, as exploited in the wild in October 2010 by the Belmoo malware.

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How to check if you are exposed to CVE-2010-3765

Find every Mozilla Multiple Products system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2010-3765.

US federal agencies had to fix this by 2025-10-27. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Affected versions

Versions the National Vulnerability Database lists as vulnerable to CVE-2010-3765. Check the vendor advisory for the exact fixed builds before you sign anything off.

Product	Vulnerable versions
Mozilla Firefox	3.5; 3.5.1; 3.5.2; 3.5.3; 3.5.4; 3.5.5 and 19 more
Mozilla Thunderbird	3.0.1; 3.0.2; 3.0.3; 3.0.4; 3.0.5; 3.0.6 and 8 more
Mozilla Seamonkey	2.0; 2.0-alpha_1; 2.0-alpha_2; 2.0-alpha_3; 2.0-beta_1; 2.0-beta_2 and 11 more

Timeline

2010-10-28 · Published in the National Vulnerability Database
2025-10-06 · Added to CISA's Known Exploited Vulnerabilities catalog, 5,457 days after it was published
2025-10-27 · Fix-by date for US federal agencies, passed 370 days ago

Vendor advisories and fixes

https://www.mozilla.org/en-US/security/advisories/mfsa2010-73

More exploited Mozilla vulnerabilities

CISA lists 13 exploited Mozilla vulnerabilities. The closest matches:

Keep going

Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.