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FirefoxWeb browser · Mozilla

CVE-2026-4709

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: GMP 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 · moderate confidence

A boundary condition vulnerability exists in the GMP (Gecko Media Plugin) component used for audio/video processing in Firefox and Thunderbird. Incorrect boundary conditions typically allow out-of-bounds memory access, potentially leading to memory corruption or code execution. This was patched in Firefox 149, Firefox ESR 115.34/140.9, Thunderbird 149, and Thunderbird 140.9.

MitigationUpdate Firefox to version 149 or later, Firefox ESR to 115.34/140.9 or later, and Thunderbird to 149/140.9 or later to obtain the patched GMP 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:< 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 menu > Help > About Firefox, or enter 'about:support' in the address bar, or run 'firefox --version' from command line
    Affected if The displayed version is earlier than 115.34.0, or falls between 128.0.0 and 140.8.x, or is earlier than 149.0 (depending on release channel)
  2. Check Thunderbird version
    Navigate to menu > Help > About Thunderbird, or run 'thunderbird --version' from command line
    Affected if The displayed version is earlier than 115.34.0, or falls between 128.0.0 and 140.8.x, or is earlier than 149.0 (depending on release channel)
  3. Identify Firefox ESR version
    In 'about:support' page, look for 'Version' field or run 'firefox --version' to see if it shows ESR in the version string (e.g., 115.x ESR)
    Affected if The ESR version is earlier than 115.34.0 or falls between 128.x and 140.8.x
  4. Verify GMP component is present
    Navigate to 'about:support' in Firefox/Thunderbird and look for 'Gecko Media Plugin' or 'GMP' in the 'Graphics' or 'Plugins' section
    Affected if GMP component is listed as present and active for audio/video processing

The environment is affected if Firefox, Firefox ESR, or Thunderbird is installed with a version number that falls within the affected ranges and the GMP component is enabled for media playback.

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 Firefox to version 149 or later, Firefox ESR to 115.34/140.9 or later, and Thunderbird to 149/140.9 or later to obtain the patched GMP component.

Recommended fix High confidence

Firefox 149 (standard) or Firefox ESR 115.34/140.9 depending on current branch; Thunderbird 149 or Thunderbird ESR 140.9

  1. 1. Check current Firefox or Thunderbird version by navigating to about:support (Firefox) or Help > About Thunderbird (Thunderbird)
  2. 2. If using standard Firefox release and version is < 149.0, upgrade to Firefox 149 or later
  3. 3. If using Firefox ESR with version < 115.34.0, upgrade to Firefox ESR 115.34 or later
  4. 4. If using Firefox ESR with version >= 128.0 and < 140.9.0, upgrade to Firefox ESR 140.9 or later
  5. 5. If using Thunderbird and version < 149.0, upgrade to Thunderbird 149 or later
  6. 6. If using Thunderbird ESR with version >= 128.0 and < 140.9.0, upgrade to Thunderbird 140.9 or later
  7. 7. Restart the application after upgrade
  8. 8. Verify the fix by checking the version again and confirming it matches or exceeds the appropriate fixed release
Caveat Upgrades may include feature changes; ensure compatibility with existing extensions and workflows before deploying in production environments

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.

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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-2026-4709 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