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FirefoxWeb browser · Mozilla

CVE-2026-8954

HIGH · 7.5 CVSS v3.1 Published 2026-05-19
Fix available
A fix is available. Upgrade to 140.11 / 140.11.0 or later.
See remediation →
84/100
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, integer overflow in the Audio/Video component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

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

An integer overflow exists in Firefox and Thunderbird's Audio/Video component due to incorrect boundary conditions. This memory corruption vulnerability could potentially allow remote attackers to execute arbitrary code or cause denial of service via specially crafted media content.

MitigationUpgrade affected installations to Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11 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:< 140.11.0< 151.0.0
ThunderbirdApplication
Affected:< 140.11

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
High
Integrity
None
Availability
None

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

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

  1. Check if Mozilla Firefox is installed
    Open terminal or command prompt and run: firefox --version (Linux/macOS) or check Help > About Firefox in the application (Windows/macOS)
    Affected if Firefox is installed and version is below 140.11.0 or below 151.0.0
  2. Check if Mozilla Thunderbird is installed
    Open terminal or command prompt and run: thunderbird --version (Linux/macOS) or check Help > About Thunderbird in the application (Windows/macOS)
    Affected if Thunderbird is installed and version is below 140.11
  3. Verify the exact Firefox version number
    Run firefox --version or access about:support in Firefox address bar to view the full version string including the revision number
    Affected if Version is any release below 140.11.0 (e.g., 140.10.x, 139.x) or below 151.0.0 (e.g., 150.x, 149.x)
  4. Confirm Audio/Video media playback usage
    The vulnerability is in the Audio/Video component. Check if the user regularly plays media files or streams video/audio content in the browser or email client
    Affected if Media playback features are actively used; exploitation requires processing specially crafted media content

User is affected if Firefox version is below 140.11.0 or below 151.0.0, or Thunderbird version is below 140.11, AND the Audio/Video component processes untrusted media content.

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 140.11 / 140.11.0 / 151.0.0 or later
Fixed in 140.11140.11.0151.0.0
Interim mitigation

Upgrade affected installations to Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11 or later to remediate this vulnerability.

Recommended fix Moderate confidence

Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11 (depending on product and release channel)

  1. Check current Firefox or Thunderbird version via Help > About Firefox/Thunderbird
  2. Download Firefox 151 (or Firefox ESR 140.11 for ESR users) from www.mozilla.org
  3. Download Thunderbird 151 or Thunderbird 140.11 from www.mozilla.org
  4. Install the downloaded update following the standard upgrade process
  5. Restart the application after installation
  6. Verify the version has been updated to the fixed release
Caveat Mozilla security releases typically have minimal breaking changes; review the Mozilla Security Advisories at www.mozilla.org for any noted compatibility issues

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

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-2026-8954 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