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FirefoxWeb browser · Mozilla

CVE-2026-8091

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-07
Fix available
A fix is available. Upgrade to 115.35.2 / 140.10.1 or later.
See remediation →
100/100
Remediation priority · Urgent
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 150, Thunderbird 150, Firefox ESR 140.10.1, Thunderbird 140.10.1, and Firefox ESR 115.35.2.

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

Incorrect boundary conditions in the Audio/Video Playback component of Firefox and Thunderbird allow memory corruption during media playback, likely enabling remote code execution. This is a boundary condition vulnerability (potentially buffer overflow or out-of-bounds read/write) in the media processing code.

MitigationUpdate Firefox to version 150 or later (ESR 115.35.2+ or 140.10.1+), and Thunderbird to version 150 or later (or 140.10.1+), or apply equivalent security patches.

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:< 115.35.2>= 140.0, < 140.10.1
ThunderbirdApplication
Affected:>= 140.0, < 140.10.1

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
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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 the installed Mozilla product
    Check if Firefox or Thunderbird is installed. On Windows, look in Program Files. On macOS, check /Applications. On Linux, check package manager or /usr/lib/firefox or /usr/lib/thunderbird.
    Affected if Either Firefox or Thunderbird is installed
  2. Determine Firefox version
    Open Firefox, go to Menu > Help > About Firefox, or navigate to about:support, or run 'firefox --version' from command line.
    Affected if Version is < 115.35.2 OR version is >= 140.0 AND < 140.10.1
  3. Determine Thunderbird version
    Open Thunderbird, go to Menu > Help > About Thunderbird, or navigate to about:support, or run 'thunderbird --version' from command line.
    Affected if Version is >= 140.0 AND < 140.10.1
  4. Verify media playback component is present
    The vulnerable Audio/Video Playback component is included by default in Firefox and Thunderbird installations. Confirm the application has media playback capability by attempting to play an audio or video file in the browser or email client.
    Affected if Media playback functionality exists in the application

You are affected if you have Firefox version < 115.35.2, Firefox 140.0-140.10.0, or Thunderbird 140.0-140.10.0 installed, as these versions contain the vulnerable Audio/Video Playback component with the boundary condition error.

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 115.35.2 / 140.10.1 or later
Fixed in 115.35.2140.10.1
Interim mitigation

Update Firefox to version 150 or later (ESR 115.35.2+ or 140.10.1+), and Thunderbird to version 150 or later (or 140.10.1+), or apply equivalent security patches.

Recommended fix High confidence

Firefox ESR 115.35.2, Firefox 140.10.1, or Firefox 150; Thunderbird 140.10.1 or Thunderbird 150

  1. Check current Firefox version: Menu > Help > About Firefox (or enter 'about:support' in URL bar)
  2. Check current Thunderbird version: Menu > Help > About Thunderbird
  3. For Firefox: If version is < 115.35.2, upgrade to Firefox ESR 115.35.2
  4. For Firefox: If version is >= 140.0 and < 140.10.1, upgrade to Firefox 140.10.1 or Firefox 150
  5. For Thunderbird: If version is >= 140.0 and < 140.10.1, upgrade to Thunderbird 140.10.1 or Thunderbird 150
  6. Download updates from www.mozilla.org or use the application's built-in update mechanism (Menu > Help > Check for Updates)
  7. Restart the application after applying the update
Caveat Standard upgrade risk: verify compatibility with any browser extensions or custom configurations

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

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

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-2026-8091 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