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Actively exploited

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.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 6 Oct 2025.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • It has been in the catalogue for 396 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

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.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Mozilla Multiple Products. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

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

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 27 Oct 2025 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Mozilla Flaws

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CVE-2024-9680 · RansomwareMozilla Firefox Use-After-Free VulnerabilityAdded 15 Oct 2024CVE-2016-9079Mozilla Firefox, Firefox ESR, and Thunderbird Use-After-Free VulnerabilityAdded 22 Jun 2023CVE-2015-4495Mozilla Firefox Security Feature Bypass VulnerabilityAdded 25 May 2022CVE-2019-11707Mozilla Firefox and Thunderbird Type Confusion VulnerabilityAdded 23 May 2022CVE-2019-11708Mozilla Firefox and Thunderbird Sandbox Escape VulnerabilityAdded 23 May 2022CVE-2013-1690Mozilla Firefox and Thunderbird Denial-of-Service VulnerabilityAdded 28 Mar 2022

All 13 exploited Mozilla vulnerabilities

Not Sure If You Are Exposed?

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2010-3765
  3. CVE record: CVE-2010-3765
  4. FIRST EPSS
  5. mozilla.org/en-US/security/advisories/mfsa2010-73
  6. securityfocus.com/bid/44425
  7. rhn.redhat.com/errata/RHSA-2010-0812.html
  8. bugzilla.mozilla.org/show_bug.cgi?id=607222#c53
  9. vupen.com/english/advisories/2010/2837
  10. bugzilla.redhat.com/show_bug.cgi?id=646997
  11. support.avaya.com/css/P8/documents/100114335
  12. secunia.com/advisories/41965