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FirefoxWeb browser · Mozilla

CVE-2026-6753

HIGH · 7.3 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 140.10.0 / 150.0 or later.
See remediation →
82/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
Incorrect boundary conditions in the WebRTC component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

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 confidence

This is a client-side vulnerability in the WebRTC component of Firefox and Thunderbird involving incorrect boundary conditions, likely allowing memory corruption or out-of-bounds access. The CVSS 7.3 indicates high severity with network-exploitable impact. The vulnerability was patched in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

MitigationUpdate affected installations to Firefox 150+, Firefox ESR 140.10+, Thunderbird 150+, or Thunderbird 140.10+ to remediate this vulnerability.

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
Affected:< 140.10.0< 150.0
ThunderbirdApplication
Affected:>= 140.0, < 140.10.0

CVSS 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
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

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 checks

Work through these to decide whether this CVE applies to you.

  1. Check Firefox version
    Navigate to Firefox menu > Help > About Firefox, or enter 'about:support' in the address bar. Note the version number displayed.
    Affected if The installed version is less than 140.10.0 OR is between 140.10.0 and 149.x (i.e., less than 150.0)
  2. Check Thunderbird version
    Navigate to Thunderbird menu > Help > About Thunderbird, or enter 'about:support' in the address bar. Note the version number displayed.
    Affected if The installed version is 140.0 or higher but less than 140.10.0
  3. Confirm WebRTC is enabled
    Enter 'about:config' in the address bar, search for 'media.peerconnection.enabled'. Verify this preference is set to true (enabled).
    Affected if WebRTC is enabled (media.peerconnection.enabled = true) - this is required for the vulnerable WebRTC component to be active
  4. Check for ESR branch usage
    In about:support, look for the 'Version' field. If it contains 'ESR' (e.g., 115.x ESR), note this is the Extended Support Release branch.
    Affected if Using Firefox ESR versions below 140.10.0

You are affected if you run Firefox < 150.0 (or Firefox ESR < 140.10.0) or Thunderbird 140.0-140.9.x with WebRTC enabled.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 140.10.0 / 150.0 or later
Fixed in 140.10.0150.0
Interim mitigation

Update affected installations to Firefox 150+, Firefox ESR 140.10+, Thunderbird 150+, or Thunderbird 140.10+ to remediate this vulnerability.

Recommended fix High confidence

Firefox 150 (or Firefox ESR 140.10); Thunderbird 150 (or Thunderbird 140.10)

  1. Check current Firefox version by navigating to Help > About Firefox
  2. Check current Thunderbird version by navigating to Help > About Thunderbird
  3. Download Firefox 150 or Firefox ESR 140.10 from the official Mozilla website (www.mozilla.org)
  4. Download Thunderbird 150 or Thunderbird 140.10 from the official Mozilla website (www.mozilla.org)
  5. Close all Firefox/Thunderbird instances
  6. Run the installer for the appropriate fixed version
  7. Restart the browser/application after installation completes
  8. Verify the installed version matches the fixed release (150.x or 140.10.x)

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-6753 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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