FirefoxWeb browser · Mozilla
CVE-2021-29966
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 · uneditedMozilla developers reported memory safety bugs present in Firefox 88. 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 affects Firefox < 89.
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 vulnerability in Firefox versions prior to 89 where Mozilla developers identified memory corruption bugs that could potentially be exploited to run arbitrary code.
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
>= 78.11.0, < 89.0CVSS 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
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 version in the browserOpen a new tab and navigate to about:firefox. The version number is displayed at the top of the page under the Firefox logo.Affected if The displayed version is 78.11.0, 78.12.0, 78.13.0, or any version from 78.11.0 up to but not including 89.0
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Check Firefox version via command lineOpen a terminal or command prompt and run 'firefox --version' (Linux/macOS) or 'firefox -v'. On Windows, you can also right-click the Firefox executable, select Properties, and view the Details tab for the version.Affected if The reported version falls within the range 78.11.0 to 88.x (any version less than 89.0)
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Verify version against affected rangeCompare your installed version number to the affected range: versions 78.11.0 through 88.x are vulnerable. Versions below 78.11.0 or at and above 89.0 are not affected.Affected if Your installed version is >= 78.11.0 AND < 89.0, meaning you are running a vulnerable version
You are affected if your Firefox version is 78.11.0 or any version up to 88.x; you are NOT affected if your version is below 78.11.0 or 89.0 and above.
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 · scoped89.0
Upgrade Firefox to version 89 or later to patch the memory safety issues.
Firefox 89.0 or later (latest stable release)
- Check current Firefox version via Help > About Firefox
- Download Firefox 89.0 or later from https://www.mozilla.org/firefox/
- Install the Firefox 89.0+ update or upgrade to the latest stable release
- Restart Firefox after the update
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 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 $2,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-29966 — 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-2021-29966 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