FirefoxWeb browser · Mozilla
CVE-2026-2799
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 · uneditedUse-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148 and Thunderbird 148.
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 use-after-free vulnerability in the DOM: Core & HTML component allows an attacker to potentially execute arbitrary code by continuing to use a freed memory pointer. This memory corruption issue in Firefox and Thunderbird has a critical CVSS score of 9.8 due to the potential for complete system compromise.
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
< 148.0< 148.0CVSS 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 Firefox versionOpen Firefox and navigate to Help > About Firefox, or run 'firefox --version' from command lineAffected if Installed version is earlier than 148.0
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Check Thunderbird versionOpen Thunderbird and navigate to Help > About Thunderbird, or run 'thunderbird --version' from command lineAffected if Installed version is earlier than 148.0
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Compare against affected rangeVerify the exact version number against the affected range (versions prior to 148.0)Affected if Either Firefox or Thunderbird is installed with a version number below 148.0
You are affected if either Mozilla Firefox or Thunderbird is installed with a version lower than 148.0, as the use-after-free vulnerability exists in the DOM Core & HTML component of those versions.
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 · scoped148.0
Upgrade to Firefox 148 or Thunderbird 148 or later to apply the patched version. Organizations should ensure all instances of the affected software are updated.
Firefox 148.0+ and Thunderbird 148.0+
- Back up bookmarks, passwords, and any critical local data before upgrading
- Upgrade Firefox to version 148.0 or later
- Upgrade Thunderbird to version 148.0 or later
- Restart the applications after upgrading to ensure the patched version is fully loaded
- Verify the installed version by checking About Firefox/About Thunderbird to confirm the update was successful
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 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 $1,424.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-2799 — 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-2026-2799 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