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FirefoxWeb browser · Mozilla

CVE-2026-7321

CRITICAL · 9.6 CVSS v3.1 Published 2026-04-28
Fix available
A fix is available. Upgrade to 140.10.1 / 150.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges

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
Sandbox escape due to incorrect boundary conditions in the WebRTC: Networking component. This vulnerability was fixed in Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, and Thunderbird 140.10.1.

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 confidence

A sandbox escape vulnerability exists in the WebRTC Networking component due to incorrect boundary conditions. This allows an attacker to break out of the sandboxed environment in Firefox and Thunderbird, potentially executing arbitrary code with elevated privileges.

MitigationUpdate affected software to Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, or Thunderbird 140.10.1 or later 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:< 140.10.1< 150.0
ThunderbirdApplication
Affected:< 140.10.1< 150.0

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
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/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 checks

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

  1. Identify installed Firefox version
    In Firefox, go to Menu > Help > About Firefox, or run 'firefox --version' from command line. Record the full version number shown.
    Affected if The version is less than 140.10.1 or between 141.0 and 149.x (since versions < 150.0 are affected)
  2. Identify installed Thunderbird version
    In Thunderbird, go to Menu > Help > About Thunderbird, or run 'thunderbird --version' from command line. Record the full version number shown.
    Affected if The version is less than 140.10.1 or between 141.0 and 149.x (since versions < 150.0 are affected)
  3. Confirm WebRTC is enabled in Firefox
    In Firefox address bar, type 'about:config', press Enter, search for 'media.peerconnection.enabled'. Verify the value is set to true (enabled).
    Affected if The WebRTC peer connection setting is enabled (value is true). The vulnerability only applies when WebRTC networking is active.
  4. Confirm WebRTC is enabled in Thunderbird
    In Thunderbird, go to Account Settings > Advanced > Config Editor (or type 'about:config' in the mail composition window). Search for 'media.peerconnection.enabled'. Verify the value is set to true (enabled).
    Affected if The WebRTC peer connection setting is enabled (value is true). The vulnerability only applies when WebRTC networking is active.
  5. Verify sandbox is active
    In Firefox or Thunderbird, go to about:config and check 'security.sandbox.content.level' (Firefox) or 'security.sandbox.mail.level' (Thunderbird). Ensure the value is greater than 0, indicating sandboxing is enabled.
    Affected if The sandbox level is greater than 0. This is a sandbox escape vulnerability, so it only affects systems where the sandbox is actually enabled.

You are affected if you run Firefox or Thunderbird with a version below 150.0 (and not 140.10.1+) AND have WebRTC peer connection enabled AND have the sandbox protection active.

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 140.10.1 / 150.0 or later
Fixed in 140.10.1150.0
Interim mitigation

Update affected software to Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, or Thunderbird 140.10.1 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, or Thunderbird 140.10.1

  1. Check current Firefox version by navigating to menu > Help > About Firefox
  2. Check current Thunderbird version by navigating to menu > Help > About Thunderbird
  3. For Firefox: Update to version 150 or later (or Firefox ESR 140.10.1 or later for enterprise deployments)
  4. For Thunderbird: Update to version 150 or later (or Thunderbird 140.10.1 or later for enterprise deployments)
  5. Restart the browser/application after update completes
  6. Verify the installed version reflects the update
Caveat Standard Firefox/Thunderbird upgrade; some legacy add-ons may require updates for compatibility with version 150

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
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

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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-2026-7321 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