FirefoxWeb browser · Mozilla
CVE-2026-4704
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 · uneditedDenial-of-service in the WebRTC: Signaling component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
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 denial-of-service vulnerability exists in the WebRTC signaling component of Firefox and Thunderbird. The vulnerability allows remote attackers to cause a denial of service (application hang or crash) via crafted WebRTC signaling messages. The CVSS 7.5 score indicates network-exploitable DoS that doesn't require authentication.
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
< 140.9.0< 149.0CVSS 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
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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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Identify installed Firefox versionNavigate to Firefox menu > Help > About Firefox, or enter 'about:support' in the address bar and locate the 'Version' fieldAffected if Version is earlier than 140.9.0 or falls between 140.9.0 and 148.x (any version before 149.0)
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Identify installed Thunderbird versionNavigate to Thunderbird menu > Help > About Thunderbird, or enter 'about:support' in the address bar and locate the 'Version' fieldAffected if Version is earlier than 140.9.0 or falls between 140.9.0 and 148.x (any version before 149.0)
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Verify WebRTC is enabledEnter 'about:config' in the address bar, search for 'media.peerconnection.enabled' and confirm it is set to trueAffected if WebRTC is enabled (this is the default setting; the vulnerability only affects systems with WebRTC functionality active)
You are affected if you run Firefox or Thunderbird version 149.0 or earlier AND WebRTC is enabled in your configuration, since the DoS vulnerability can be triggered via crafted WebRTC signaling messages.
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 · scoped140.9.0149.0
Update affected installations to Firefox 149, Firefox ESR 140.9, Thunderbird 149, or Thunderbird 140.9. No additional configuration changes required; standard software update process suffices.
Firefox 149 (regular release) or Firefox ESR 140.9
- Open Firefox and navigate to Help > About Firefox to check current version
- If version is below 149.0, download Firefox 149 or later from the official Mozilla website (www.mozilla.org)
- Run the downloaded installer and follow the prompts to upgrade
- Alternatively, for enterprise environments, download Firefox ESR 140.9 from Mozilla's official channels
- After installation, verify the version by checking Help > About Firefox shows 149.0 or later (or 140.9 for ESR)
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 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 $1,200.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-4704 — 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-2026-4704 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