FirefoxWeb browser · Mozilla
CVE-2025-49709
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 · uneditedCertain canvas operations could have lead to memory corruption. This vulnerability was fixed in Firefox 139.0.4.
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 · moderate confidenceA memory corruption vulnerability exists in Firefox's canvas rendering implementation, potentially allowing arbitrary code execution via specially crafted canvas operations. The issue carries a critical CVSS 9.8 rating, indicating potential for complete system compromise through the browser attack surface.
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
< 139.0.4CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Check installed Firefox versionOpen Firefox, click the menu button (three horizontal lines), then click Help > About Firefox. The version number will display in the window that opens.Affected if The displayed version number is less than 139.0.4 (e.g., 139.0, 138.x, 137.x, etc.)
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Check Firefox version via command lineRun 'firefox --version' in terminal/command prompt, or on Windows check the executable properties of the firefox.exe file.Affected if The reported version is lower than 139.0.4
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Verify canvas module is enabledIn Firefox address bar, type 'about:config' and press Enter. Search for 'canvas.enabled' preference.Affected if The preference 'canvas.enabled' is set to true (this is the default setting) - combined with an affected version, the system is vulnerable
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Check for multiple Firefox installationsOn Windows, check Program Files and Program Files (x86) for multiple Firefox folders. On macOS, check /Applications and ~/Applications. On Linux, check /usr/lib/firefox and /opt.Affected if Any Firefox installation found is version 139.0.3 or earlier
A user is affected if any installed Firefox version is below 139.0.4 and the canvas rendering feature remains enabled (the default state).
Generated from the published advisory. Verify against your own configuration.
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 · scoped139.0.4
Update Firefox to version 139.0.4 or later to remediate this vulnerability. Organizations should ensure endpoint protection and consider browser version management policies.
Firefox 139.0.4
- Check your current Firefox version by clicking Help > About Firefox
- Navigate to https://www.mozilla.org/en-US/firefox/ or use the built-in update feature (Firefox will typically prompt you automatically)
- Download Firefox 139.0.4 or later from the official Mozilla website
- Run the installer and follow the prompts to complete the update
- Restart Firefox to ensure the update is fully applied
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation1.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,456.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-49709 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-49709 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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