FirefoxWeb browser · Mozilla
CVE-2021-38498
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 · uneditedDuring process shutdown, a document could have caused a use-after-free of a languages service object, leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 93, Thunderbird < 91.2, and Firefox ESR < 91.2.
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 · high confidenceA use-after-free vulnerability exists in the Firefox languages service object during process shutdown. When a document is being cleaned up during shutdown, it can prematurely free a languages service object while a reference to it remains, leading to memory corruption and potential exploitation.
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
< 93.0
Firefox EsrWeb browser
< 91.2< 91.2CVSS 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
- 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 versionOpen Firefox and navigate to Help > About Firefox, or type 'about:support' in the address bar to view the version number under Application BasicsAffected if Version is below 93.0 (for standard Firefox)
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Identify installed Firefox ESR versionOpen Firefox ESR and navigate to Help > About Firefox ESR, or check the package manager if installed via system packageAffected if Version is below 91.2 (for Firefox ESR)
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Identify installed Thunderbird versionOpen Thunderbird and navigate to Help > About Thunderbird, or check the package manager if installed via system packageAffected if Version is below 91.2 (for Thunderbird)
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Verify product type if unsureCheck Help > About for the exact product name - standard Firefox will show 'Mozilla Firefox', ESR will show 'Mozilla Firefox ESR', Thunderbird will show 'Mozilla Thunderbird'Affected if Running any affected product variant below its threshold version
You are affected if any installed Firefox version is below 93.0, or any Firefox ESR/Thunderbird version is below 91.2.
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 · scoped91.293.0
Update affected products to the fixed versions: Firefox 93+, Thunderbird 91.2+, or Firefox ESR 91.2+. Alternatively, remove or disable the affected software if patching is not immediately feasible.
Firefox 93.0, Firefox ESR 91.2, or Thunderbird 91.2
- Upgrade Firefox to version 93.0 or higher
- Upgrade Firefox ESR to version 91.2 or higher
- Upgrade Thunderbird to version 91.2 or higher
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 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 $1,696.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-38498 — 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-2021-38498 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