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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 27 Oct 2025.
FirefoxWeb browser · Mozilla

CVE-2010-3765

CRITICAL · 9.8 CVSS v3.1 Published 2010-10-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Memory corruption vulnerability in Mozilla Firefox, Thunderbird, and SeaMonkey's layout engine (nsCSSFrameConstructor) where improper handling of the appendChild method, incorrect index tracking during frame creation leads to memory corruption, allowing remote attackers to execute arbitrary code when JavaScript is enabled.

MitigationUpgrade to patched versions (Firefox 3.5.15/3.6.12, Thunderbird 3.1.7/3.0.11, SeaMonkey 2.0.10) or disable JavaScript in affected applications.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FirefoxWeb browser
Affected:= 3.5= 3.5.1= 3.5.2= 3.5.3= 3.5.4= 3.5.5= 3.5.6= 3.5.7= 3.5.8= 3.5.9= 3.5.10= 3.5.11
ThunderbirdApplication
Affected:= 3.0.1= 3.0.2= 3.0.3= 3.0.4= 3.0.5= 3.0.6= 3.0.7= 3.0.8= 3.0.9= 3.1.1= 3.1.2= 3.1.3
SeamonkeyApplication
Affected:= 2.0= 2.0.1= 2.0.2= 2.0.3= 2.0.4= 2.0.5= 2.0.6= 2.0.7= 2.0.8= 2.0.9

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Mozilla product
    Check the application name and executable. Firefox typically shows 'Mozilla Firefox' in title bar, Thunderbird shows 'Mozilla Thunderbird', SeaMonkey shows 'SeaMonkey'. On Windows check Add/Remove Programs or the executable properties.
    Affected if The product is Firefox, Thunderbird, or SeaMonkey from the affected version list.
  2. Find Firefox version
    In Firefox go to Help > About Firefox, or type 'about:support' in the address bar, or check the version from the application's Help menu. On Linux check the package manager or execute 'firefox --version'. On Windows right-click the firefox.exe and view Properties > Details.
    Affected if Version is 3.5.1 through 3.5.11 inclusive.
  3. Find Thunderbird version
    In Thunderbird go to Help > About Thunderbird, or check the version from the application's Help menu. On Linux check the package manager or execute 'thunderbird --version'. On Windows right-click thunderbird.exe and view Properties > Details.
    Affected if Version is 3.0.1 through 3.0.9, or 3.1.1 through 3.1.3 inclusive.
  4. Find SeaMonkey version
    In SeaMonkey go to Help > About SeaMonkey, or check the version from the application's Help menu. On Linux check the package manager or execute 'seamonkey --version'. On Windows right-click seamonkey.exe and view Properties > Details.
    Affected if Version is 2.0 through 2.0.9 inclusive.
  5. Compare against affected ranges
    Match your discovered version exactly to the list: Firefox 3.5.x (3.5.1-3.5.11), Thunderbird 3.0.x (3.0.1-3.0.9) and 3.1.x (3.1.1-3.1.3), SeaMonkey 2.0.x (2.0-2.0.9). Note that Firefox 3.5.0 and Thunderbird 3.0.0 are NOT listed as affected in this CVE.
    Affected if Your installed version exactly matches one of the versions listed in the affected products and versions.

You are affected if you have Firefox 3.5.1-3.5.11, Thunderbird 3.0.1-3.0.9 or 3.1.1-3.1.3, or SeaMonkey 2.0-2.0.9 installed and use the browser to visit untrusted web pages that could trigger the DOM frame construction flaw via appendChild.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to patched versions (Firefox 3.5.15/3.6.12, Thunderbird 3.1.7/3.0.11, SeaMonkey 2.0.10) or disable JavaScript in affected applications.

Recommended fix High confidence

Firefox 3.5.15+/3.6.12+, Thunderbird 3.0.10+/3.1.6+, SeaMonkey 2.0.10+

  1. Upgrade Firefox 3.5.x to version 3.5.15 or later
  2. Upgrade Firefox 3.6.x to version 3.6.12 or later
  3. Upgrade Thunderbird 3.0.x to version 3.0.10 or later
  4. Upgrade Thunderbird 3.1.x to version 3.1.6 or later
  5. Upgrade SeaMonkey 2.0.x to version 2.0.10 or later
  6. After upgrading, verify the installed version matches the expected fixed release
Caveat These are major version upgrades to older, unsupported product lines; ensure compatibility with existing systems and test in a non-production environment before deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Exploited in the wild — priority engagement
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2010-3765 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data