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FirefoxWeb browser · Mozilla

CVE-2026-4695

HIGH · 7.5 CVSS v3.1 Published 2026-03-24
Fix available
A fix is available. Upgrade to 140.9.0 / 149.0 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 in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

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 · moderate confidence

A boundary condition vulnerability in the Web Codecs component of Firefox and Thunderbird allows incorrect memory access during audio/video encoding or decoding operations. This type of flaw typically involves improper bounds checking that could lead to out-of-bounds read/write operations, potentially enabling memory corruption or information disclosure.

MitigationUpdate affected installations to Firefox 149+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ to obtain the patched version of the Web Codecs component.

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:< 140.9.0< 149.0

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
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 or Thunderbird version
    In Firefox: Go to Menu > Help > About Firefox. In Thunderbird: Go to Menu > Help > About Thunderbird. The version number is displayed in the window that opens.
    Affected if The displayed version is below 149.0 (for standard releases) or below 140.9.0 (for ESR releases)
  2. Confirm the Web Codecs API is in use
    Check if the application processes web-based audio or video content, or inspect browser console for Web Codecs API usage (e.g., 'VideoDecoder', 'AudioDecoder' JavaScript calls) in any loaded web pages or extensions.
    Affected if The Web Codecs API is actively being used to decode audio or video content
  3. Check for third-party extensions using Web Codecs
    Review installed extensions for any that handle media processing, video editing, or audio manipulation, as these may invoke Web Codecs APIs.
    Affected if Extensions that leverage the Web Codecs component are installed and active

If the installed Firefox version is below 149.0 (or ESR below 140.9.0) AND the Web Codecs API is being actively used to process media, the environment is likely affected by this boundary condition vulnerability.

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 140.9.0 / 149.0 or later
Fixed in 140.9.0149.0
Interim mitigation

Update affected installations to Firefox 149+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ to obtain the patched version of the Web Codecs component.

Recommended fix High confidence

Firefox 149.0 (or Firefox ESR 140.9)

  1. 1. Open Firefox and navigate to Menu > Help > About Firefox (or go to about:support)
  2. 2. Click 'Check for Updates' or let automatic checking occur
  3. 3. If an update is available, click 'Download the Update' and wait for it to complete
  4. 4. Click 'Restart to update Firefox' when prompted
  5. 5. After restart, verify the version by going to Menu > Help > About Firefox - confirm version 149.0 or later (or 140.9 for ESR)

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
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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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-2026-4695 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