FirefoxWeb browser · Mozilla
CVE-2021-23982
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 · uneditedUsing techniques that built on the slipstream research, a malicious webpage could have scanned both an internal network's hosts as well as services running on the user's local machine utilizing WebRTC connections. This vulnerability affects Firefox ESR < 78.9, Firefox < 87, and Thunderbird < 78.9.
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 malicious webpage can leverage WebRTC connection handling to perform port scanning on both internal network hosts and the user's local machine. This enables an attacker to conduct network reconnaissance and discover running services by observing WebRTC connection behavior, bypassing typical browser sandbox restrictions.
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
< 87.0
Firefox EsrWeb browser
< 78.9< 78.9CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
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 versionNavigate to Menu > Help > About Firefox (or enter 'about:support' in address bar) to view the installed version numberAffected if Version is below 87.0 for standard Firefox, or below 78.9 for Firefox ESR
-
Check Thunderbird versionNavigate to Menu > Help > About Thunderbird to view the installed version numberAffected if Version is below 78.9
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Verify WebRTC status in FirefoxEnter 'about:config' in the address bar, search for 'media.peerconnection.enabled' and check if the value is set to trueAffected if media.peerconnection.enabled is true (WebRTC enabled)
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Verify WebRTC status in ThunderbirdCheck Thunderbird settings or enter 'about:config' and search for 'media.peerconnection.enabled' to confirm if WebRTC is enabledAffected if media.peerconnection.enabled is true (WebRTC enabled)
User is affected if running Firefox < 87.0 (or ESR < 78.9) or Thunderbird < 78.9 with WebRTC enabled, allowing malicious webpages to perform port scanning via WebRTC connections.
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.
From vendor data78.987.0
Update to Firefox 87+, Firefox ESR 78.9+, or Thunderbird 78.9+ to patch the WebRTC port scanning vector. Alternatively, disable WebRTC in browser settings if updates are not immediately feasible.
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-2021-23982 — 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-2021-23982 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
- No spam, self-promotion, credentials, or personal data