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FirefoxWeb browser · Mozilla

CVE-2026-8963

HIGH · 7.5 CVSS v3.1 Published 2026-05-19
Fix available
A fix is available. Upgrade to 151.0.0 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
Spoofing issue in the Web Speech component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.

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 spoofing vulnerability in the Web Speech component of Firefox and Thunderbird allows attackers to manipulate speech synthesis or recognition outputs, potentially tricking users into believing fabricated voice interactions are legitimate. The flaw was addressed in versions 151 of both products.

MitigationUpdate Firefox and Thunderbird installations to version 151 or later to remediate this vulnerability. In enterprise environments, test for compatibility with internal applications using the Web Speech API before broad deployment.

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:< 151.0.0
ThunderbirdApplication
Affected:< 151.0.0

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
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 checks

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

  1. Identify installed Mozilla product
    Check if Firefox or Thunderbird is installed by looking for the executable: Windows - check Program Files/Mozilla Firefox or Mozilla Thunderbird folders, or run 'firefox --version' or 'thunderbird --version' in command prompt. Linux - check /usr/bin/firefox or /usr/bin/thunderbird, or use package manager. macOS - check /Applications/Firefox.app or /Applications/Thunderbird.app
    Affected if Either Firefox or Thunderbird is installed on the system
  2. Determine Firefox version
    For Firefox: Enter 'about:support' in the address bar and look at the 'Version' field, or run 'firefox --version' in command line
    Affected if Firefox version is below 151.0.0 (e.g., 150.x, 150.0, 149.x, etc.)
  3. Determine Thunderbird version
    For Thunderbird: Enter 'about:support' in the address bar and look at the 'Version' field, or run 'thunderbird --version' in command line
    Affected if Thunderbird version is below 151.0.0 (e.g., 150.x, 150.0, 149.x, etc.)

The environment is affected if either Firefox or Thunderbird is installed with a version number lower than 151.0.0, since the Web Speech API spoofing vulnerability exists in all prior versions.

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 151.0.0 or later
Fixed in 151.0.0
Interim mitigation

Update Firefox and Thunderbird installations to version 151 or later to remediate this vulnerability. In enterprise environments, test for compatibility with internal applications using the Web Speech API before broad deployment.

Recommended fix High confidence

Firefox 151.0.0 and Thunderbird 151.0.0

  1. Check the current version of Firefox or Thunderbird by navigating to Menu > Help > About Firefox/Thunderbird
  2. Download Firefox 151.0.0 or later from the official Mozilla website (www.mozilla.org)
  3. Download Thunderbird 151.0.0 or later from the official Mozilla website (www.mozilla.org)
  4. Run the installer and follow the prompts to complete the upgrade
  5. Restart the application after the update is installed
  6. Verify the version by checking Menu > Help > About to confirm the installation of version 151.0.0 or later

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,390
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.

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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-2026-8963 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