Mozilla Firefox and Thunderbird Remote Code Execution Vulnerability (CVE-2010-3765) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTMozilla Firefox 3.5.x through 3.5.14, 3.6.x through 3.6.11, Thunderbird 3.0.x through 3.0.9, 3.1.x through 3.1.5, and SeaMonkey 2.0.x through 2.0.9 with JavaScript enabled
Remote attackers can trigger memory corruption and execute arbitrary code with the privileges of the logged-in user by enticing them to visit a specially crafted webpage
Immediately upgrade to patched versions (Firefox 3.5.15/3.6.12, Thunderbird 3.0.10/3.1.6, SeaMonkey 2.0.10 or later) or disable JavaScript as a temporary workaround
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Update your Mozilla packages to the latest secure versions using your system's package manager.
# For Debian/Ubuntu-based systems
sudo apt-get update
sudo apt-get --only-upgrade install firefox thunderbird -y
# For RedHat/CentOS/Fedora-based systems
sudo yum update firefox thunderbird -y2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, disable JavaScript in Firefox profiles to mitigate the primary attack vector.
# Append preference to disable JavaScript in all Firefox default profiles
echo "user_pref('javascript.enabled', false);" >> ~/.mozilla/firefox/*.default/user.js3. Log Audit & IoC Verification Commands
Use the following script to audit the installed Firefox version and identify if the system is running a vulnerable release.
# Check installed Firefox version and flag vulnerability status
ff_version=$(firefox --version 2>/dev/null | awk '{print $3}')
if [ ! -z '$ff_version' ]; then
echo 'Detected Firefox Version: '$ff_version
if [[ '$ff_version' =~ ^3\.5\.(1[0-4]|[0-9])$ ]] || [[ '$ff_version' =~ ^3\.6\.(1[0-1]|[0-9])$ ]]; then
echo '[WARNING] Vulnerable Firefox version detected. Upgrade immediately.'
else
echo '[OK] Firefox version is not within the primary vulnerable range.'
fi
fiBlock Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2010-3765) is a critical memory corruption flaw residing in the nsCSSFrameConstructor::ContentAppended function of the Mozilla rendering engine. When processing dynamic DOM manipulations via the appendChild method, incorrect index tracking during the creation of multiple CSS frames causes the engine to reference invalid or freed memory addresses. This behavior constitutes a classic memory safety violation (CWE-119), leading to a Use-After-Free or heap corruption condition.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a malicious website containing crafted JavaScript and HTML structures. When a vulnerable browser visits the page, the script invokes appendChild to dynamically insert elements, forcing the nsCSSFrameConstructor to rebuild layout frames. Due to the index tracking flaw, the engine corrupts heap memory, allowing the attacker to hijack the instruction pointer and execute arbitrary shellcode. This vulnerability was actively exploited in the wild in October 2010 by the 'Belmoo' malware family.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 and its inclusion in the CISA KEV catalog, this vulnerability poses an extreme risk to enterprise endpoints. Successful exploitation grants the attacker full control over the victim's workstation. This can serve as an initial access vector for lateral movement, sensitive data exfiltration, and deployment of ransomware across the corporate network.
Official Vendor Advisories & References
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.
Frequently Asked SecOps Questions (CVE-2010-3765)
FAQQ1. How critical is CVE-2010-3765 and is it actively exploited in the wild?
CVE-2010-3765 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 83.2%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2010-3765?
Primary impacted vendors include mozilla across firefox, thunderbird, seamonkey. Scope summary: Mozilla Firefox 3.5.x to 3.5.14, 3.6.x to 3.6.11 / Thunderbird 3.0.x to 3.0.9, 3.1.x to 3.1.5 / SeaMonkey 2.0.x to 2.0.9 (when JavaScript is enabled)
Q3. What temporary mitigations or workarounds exist for CVE-2010-3765 before patching?
[Mitigation] Immediately upgrade to patched versions (Firefox 3.5.15/3.6.12, Thunderbird 3.0.10/3.1.6, SeaMonkey 2.0.10 or later) or disable JavaScript as a temporary workaround Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2010-3765
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (mozilla)
View Category →Google Chrome V8 Inappropriate Implementation Sandbox Remote Code Execution Vulnerability (CVE-2026-3910)
[Affected Scope] Google Chrome and Chromium-based browsers prior to version 146.0.7680.75
Apple macOS Screen Sharing Authentication Bypass Vulnerability (CVE-2026-65400)
[Affected Scope] macOS systems running versions prior to Sequoia 15.7.9, Sonoma 14.8.9, Tahoe 26.6.1/26.7, or Golden Gate 27 with Screen Sharing or VNC services enabled
DAEMON Tools Lite Official Installer Supply Chain Attack and Trojanized Binaries (CVE-2026-8398)
[Affected Scope] DAEMON Tools Lite Windows versions 12.5.0.2421 through 12.5.0.2434 distributed between April 8, 2026, and May 5, 2026
Microsoft Windows Shell Command Injection and Security Feature Bypass (CVE-2026-96951) Advisory
[Affected Scope] All supported versions of Windows OS including Windows 10, 11, and Windows Server.
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.