CVE-2010-3765
Mozilla Multiple Products Remote Code Execution Vulnerability
Mozilla Multiple Products
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.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 6 October 2025. US federal agencies were required to remediate it by 27 October 2025.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 83.2%, which is higher than 99.7% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Frequently asked questions
Is CVE-2010-3765 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2010-3765.
What does CVE-2010-3765 affect?
CVE-2010-3765 affects Mozilla Multiple Products. 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.
How severe is CVE-2010-3765?
CVE-2010-3765 is rated CRITICAL with a CVSS base score of 9.8. EPSS puts the probability of exploitation in the next 30 days at 83.2%, higher than 99.7% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 27 October 2025.
How should organisations respond to CVE-2010-3765?
Apply the vendor patch for Mozilla Multiple Products as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.