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FirefoxWeb browser · Mozilla

CVE-2015-2731

HIGH · 10.0 CVSS v2.0 Published 2015-07-06
Fix available
A fix is available. Upgrade to after 38.1.0 or later.
See remediation →
100/100
Remediation priority · Urgent
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
Use-after-free vulnerability in the CSPService::ShouldLoad function in the microtask implementation in Mozilla Firefox before 39.0, Firefox ESR 38.x before 38.1, and Thunderbird before 38.1 allows remote attackers to execute arbitrary code by leveraging client-side JavaScript that triggers removal of a DOM object on the basis of a Content Policy.

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

A use-after-free vulnerability in Mozilla Firefox and Thunderbird's Content Security Policy (CSP) implementation allows remote attackers to execute arbitrary code. The flaw occurs in the CSPService::ShouldLoad function during DOM object removal triggered by JavaScript, causing freed memory to be accessed.

MitigationUpgrade affected products to Firefox 39.0, Firefox ESR 38.1, Thunderbird 38.1, or later versions. This is a client-side vulnerability requiring software updates rather than network configuration changes.

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:<= 38.1.0= 31.0= 31.1.0= 31.1.1= 31.3.0= 31.5.1= 31.5.2= 31.5.3= 38.0
Firefox EsrWeb browser
Affected:= 31.1= 31.2= 31.3= 31.4= 31.5= 31.6.0= 31.7.0
ThunderbirdApplication
Affected:<= 38.0.1
SolarisOperating system
Affected:= 11.3

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
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:N/AC:L/Au:N/C:C/I:C/A:C

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 Firefox version
    On Windows, check Help > About Firefox. On Linux, run 'firefox --version' or check the package manager. On macOS, run 'firefox --version' or check Application info.
    Affected if The installed version is 38.1.0 or earlier, or exactly matches 31.0, 31.1.0, 31.1.1, 31.3.0, 31.5.1, 31.5.2, 31.5.3, or 38.0
  2. Identify installed Firefox ESR version
    On Windows, check Help > About Firefox. On Linux, run 'firefox --version' or check the package manager.
    Affected if The installed version is exactly 31.1, 31.2, 31.3, 31.4, 31.5, 31.6.0, or 31.7.0
  3. Identify installed Thunderbird version
    On Windows, check Help > About Thunderbird. On Linux, run 'thunderbird --version' or check the package manager. On macOS, run 'thunderbird --version' or check Application info.
    Affected if The installed version is 38.0.1 or earlier
  4. Determine if Content Security Policy is in use
    Inspect web applications or pages being accessed for CSP headers (Content-Security-Policy HTTP response headers) or meta tags. Check browser developer tools or proxy logs for CSP enforcement.
    Affected if CSP headers or meta tags are present and being enforced - the vulnerable code path in CSPService::ShouldLoad is only triggered when CSP is active

You are affected if you are running Firefox 38.1.0 or earlier (or specific point versions listed), Firefox ESR 31.x through 31.7.0, Thunderbird 38.0.1 or earlier, or Oracle Solaris 11.3 with bundled Firefox, and you process Content Security Policy headers.

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
Upgrade available Upgrade to a release after 38.1.0
Interim mitigation

Upgrade affected products to Firefox 39.0, Firefox ESR 38.1, Thunderbird 38.1, or later versions. This is a client-side vulnerability requiring software updates rather than network configuration changes.

Recommended fix High confidence

Firefox 39.0+ or Firefox ESR 38.1+ or Thunderbird 38.1+

  1. 1. Close all instances of Firefox, Thunderbird, or related Mozilla products
  2. 2. Back up bookmarks, passwords, and important profile data
  3. 3. Download Firefox 39.0 or later from mozilla.org
  4. 4. Run the installer and follow prompts to upgrade
  5. 5. Alternatively, use the application's built-in update mechanism (Help > About > Check for Updates)
  6. 6. For Firefox ESR 31.x systems, upgrade to Firefox ESR 38.1 or later
  7. 7. For Thunderbird users, upgrade to Thunderbird 38.1 or later
  8. 8. Restart the application and verify the version in Help > About
Caveat Upgrading from Firefox 31.x to 38.1+ may cause compatibility issues with older extensions or plugins that have not been updated for newer versions

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2015-2731 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