FirefoxWeb browser · Mozilla
CVE-2024-9399
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 · uneditedA website configured to initiate a specially crafted WebTransport session could crash the Firefox process leading to a denial of service condition. This vulnerability affects Firefox < 131, Firefox ESR < 128.3, Thunderbird < 128.3, and Thunderbird < 131.
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 specially crafted WebTransport session initiated by a malicious website can cause the Firefox or Thunderbird process to crash, resulting in denial of service. The vulnerability lies in how the browser handles malformed WebTransport sessions.
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
< 128.3.0>= 129.0, < 131.0< 128.3.0>= 129.0, < 131.0CVSS 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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Check Firefox versionOpen Firefox, click the menu (three lines) > Help > About Firefox. The version number is displayed on this page.Affected if The version is less than 128.3.0, or greater than or equal to 129.0 but less than 131.0
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Check Thunderbird versionOpen Thunderbird, click the menu (three lines) > Help > About Thunderbird. The version number is displayed on this page.Affected if The version is less than 128.3.0, or greater than or equal to 129.0 but less than 131.0
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Verify WebTransport is enabled in FirefoxIn the Firefox address bar, type about:config and press Enter. In the search field, type network.webtransport. Check if the preference network.webtransport.enabled exists and is set to true.Affected if The preference exists and is set to true (this feature must be enabled for the malformed session to trigger the crash)
You are affected if you are running an affected version of Firefox (below 128.3.0, or 129.0 to 130.x) or Thunderbird (below 128.3.0, or 129.0 to 130.x) AND WebTransport is enabled in your browser settings.
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 · scoped128.3.0131.0
Update Firefox to version 131 or later, Firefox ESR to 128.3 or later, and Thunderbird to 128.3 or later. Until patched, avoid visiting untrusted websites that may attempt to trigger WebTransport sessions.
Firefox 131.0 (or ESR 128.3); Thunderbird 128.3 or 131.0
- Check current Firefox version by navigating to Menu > Help > About Firefox
- Check current Thunderbird version by navigating to Menu > Help > About Thunderbird
- Download the latest Firefox release from https://www.mozilla.org/firefox/ or Thunderbird from https://www.thunderbird.net/
- For Firefox: If current version is < 128.3.0, upgrade to 128.3.0 or later
- For Firefox: If current version is >= 129.0 and < 131.0, upgrade to 131.0 or later
- For Thunderbird: If current version is < 128.3.0, upgrade to 128.3.0 or later
- For Thunderbird: If current version is >= 129.0 and < 131.0, upgrade to 131.0 or later
- Restart the application after upgrade
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-2024-9399 — 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-2024-9399 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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- 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
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