FirefoxWeb browser · Mozilla
CVE-2026-5735
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 · uneditedMemory safety bugs present in Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2 and Thunderbird 149.0.2.
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 confidenceMemory safety bugs in Firefox 149.0.1 and Thunderbird 149.0.1 allowed memory corruption that could potentially be exploited for arbitrary code execution. The vulnerability was addressed in version 149.0.2 of both products.
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
< 149.0.2< 149.0.2CVSS 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 Menu > Help > About Firefox, or enter 'about:对话' in the address bar to display the version numberAffected if The displayed version is 149.0.1 or any version lower than 149.0.2
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Check Thunderbird versionOpen Thunderbird and navigate to Menu > Help > About Thunderbird, or enter 'about:对话' in the address bar to display the version numberAffected if The displayed version is 149.0.1 or any version lower than 149.0.2
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Check Firefox version via command lineRun 'firefox --version' or 'firefox -v' in a terminal to display the installed Firefox versionAffected if The command output shows version 149.0.1 or any version lower than 149.0.2
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Check Thunderbird version via command lineRun 'thunderbird --version' or 'thunderbird -v' in a terminal to display the installed Thunderbird versionAffected if The command output shows version 149.0.1 or any version lower than 149.0.2
You are affected if either Firefox or Thunderbird is installed with a version lower than 149.0.2, as the memory corruption vulnerability exists in version 149.0.1 and was patched in version 149.0.2.
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 · scoped149.0.2
Upgrade Firefox and Thunderbird to version 149.0.2 or later to remediate the memory safety vulnerabilities.
Firefox 149.0.2 or Thunderbird 149.0.2
- Open Firefox or Thunderbird and navigate to Help > About [Application Name] to check the current version
- In the About window, the application will automatically check for updates and prompt you to update to version 149.0.2
- Alternatively, download Firefox 149.0.2 from the official Mozilla website (www.mozilla.org) or Thunderbird 149.0.2 from the official Thunderbird website
- If using an enterprise deployment, use your organization's software distribution tools to push version 149.0.2 to end-user systems
- After updating, restart the application to ensure the security patch is fully applied
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
- Testing2.0 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 $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-5735 — 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-2026-5735 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