FirefoxWeb browser · Mozilla
CVE-2021-29990
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 and community members reported memory safety bugs present in Firefox 90. 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 < 91.
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 90 and earlier that allows memory corruption through unspecified bugs, potentially enabling arbitrary code execution. This is part of a set of memory safety issues addressed in the Firefox 91 update.
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
< 91.0CVSS 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 installed Firefox versionOpen Firefox and navigate to Help > About Firefox, or type 'about:support' in the address bar and press Enter. The version number is displayed at the top of the page.Affected if The version displayed is 90.x or earlier (for example, 90.0, 89.0, 88.0, etc.)
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Confirm version number formatNote the full version string shown in the About dialog (for example, 90.0.2 or 90.0.1). Compare the first number to the affected range.Affected if The major version number is less than 91 (for example, 90, 89, 88, or any version below 91).
If the installed Firefox version shows a number below 91.0 (such as 90.x or earlier), the environment is affected by this memory safety vulnerability.
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 · scoped91.0
Upgrade Firefox to version 91 or later to remediate this vulnerability. This is a standard software update requiring no custom code changes.
Firefox 91.0 or later
- 1. Open Firefox and navigate to Help > About Firefox to check the current version
- 2. If the version is below 91.0, Firefox should automatically check for updates. If not, download Firefox 91.0 or later from the official Mozilla website (www.mozilla.org)
- 3. Install the Firefox 91.0+ update following the on-screen prompts
- 4. Restart Firefox after the update completes
- 5. Verify the update by checking Help > About Firefox shows version 91.0 or later
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Testing1.0 h
- Review / QA0.5 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-2021-29990 — 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-2021-29990 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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