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FirefoxWeb browser · Mozilla

CVE-2026-4693

HIGH · 7.5 CVSS v3.1 Published 2026-03-24
Fix available
A fix is available. Upgrade to 115.34.0 / 140.9.0 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: Playback component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, 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 · high confidence

This is a boundary condition vulnerability in the Audio/Video Playback component of Firefox and Thunderbird. Incorrect boundary conditions typically indicate improper bounds checking during media processing, which could allow memory corruption or out-of-bounds access during playback of audio/video content.

MitigationUpdate affected installations to Firefox 149 or later, Firefox ESR 115.34/140.9 or later, or Thunderbird 140.9/149 or later. This is a client-side vulnerability that is patched via the software vendor's update mechanism.

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:< 115.34.0< 149.0>= 128.0, < 140.9.0

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. Check Firefox version
    Navigate to Firefox menu > Help > About Firefox, or enter 'about:support' in the address bar to see the version number
    Affected if Version is < 115.34.0, OR between 128.0 and 140.8.x, OR between 140.9.0 and 148.x
  2. Verify media playback component is in use
    Confirm that the system has played or can play audio/video content using Firefox's built-in media engine
    Affected if Media playback features have been used or are accessible in the browser
  3. Check Thunderbird version if applicable
    Navigate to Thunderbird menu > Help > About Thunderbird to see the version number
    Affected if Thunderbird is installed and version is < 140.9.0 (exact affected range for Thunderbird not fully specified in CVE data)

A user is affected if they run Firefox versions that fall below 115.34.0, between 128.0-140.8.x, or 140.9.0-148.x, or Thunderbird versions below 140.9.0, AND actively use media playback capabilities in the affected product.

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 115.34.0 / 140.9.0 / 149.0 or later
Fixed in 115.34.0140.9.0149.0
Interim mitigation

Update affected installations to Firefox 149 or later, Firefox ESR 115.34/140.9 or later, or Thunderbird 140.9/149 or later. This is a client-side vulnerability that is patched via the software vendor's update mechanism.

Recommended fix High confidence

Firefox 149 (standard) / Firefox ESR 115.34 / Firefox ESR 140.9 / Thunderbird 149 / Thunderbird 140.9

  1. 1. Determine which Firefox or Thunderbird product and version is currently installed.
  2. 2. Identify the appropriate upgrade path based on the installed product type:
  3. - For Firefox (standard release): upgrade to version 149 or later
  4. - For Firefox ESR 115.x: upgrade to version 115.34 or later
  5. - For Firefox ESR 128.x/140.x: upgrade to version 140.9 or later
  6. - For Thunderbird: upgrade to version 149 or later (standard) or 140.9 (ESR)
  7. 3. Download the appropriate fixed version from the official Mozilla website (www.mozilla.org) or use the application's built-in update mechanism.
  8. 4. Close all instances of the browser or email client.
Caveat Standard Mozilla upgrade; minimal risk as these are point releases within the same major version branch

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-2026-4693 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