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FirefoxWeb browser · Mozilla

CVE-2026-2757

CRITICAL · 9.8 CVSS v3.1 Published 2026-02-24
Fix available
A fix is available. Upgrade to 115.33.0 / 140.8.0 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 WebRTC: Audio/Video component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

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 WebRTC Audio/Video component of Firefox and Thunderbird. The incorrect boundary conditions likely allow memory corruption, potentially enabling remote code execution or denial of service attacks. The issue is rated critical (CVSS 9.8) and affects multiple Firefox ESR versions and Thunderbird.

MitigationApply the vendor-supplied patches by upgrading to Firefox 148, Firefox ESR 115.33/140.8, or Thunderbird 148/140.8 as appropriate for the affected 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:< 115.33.0< 148.0>= 128.0, < 140.8.0
ThunderbirdApplication
Affected:< 140.8.0< 148.0

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
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. Check installed Firefox version
    Navigate to Firefox menu > Help > About Firefox (or enter 'about:support' in the address bar). The version number is displayed at the top.
    Affected if The installed version is less than 115.33.0, or between 128.0 and 140.7.x inclusive, or less than 148.0 (if not covered by previous ranges)
  2. Check installed Thunderbird version
    Navigate to Thunderbird menu > Help > About Thunderbird. The version number is displayed at the top.
    Affected if The installed version is less than 140.8.0 or less than 148.0
  3. Verify WebRTC is in use
    This vulnerability affects WebRTC audio/video processing. Check if the browser handles WebRTC connections - look for 'WebRTC' in about:support or monitor for peer connections using webrtc-internals (enter 'webrtc-internals' in address bar).
    Affected if WebRTC connections are actively used or the WebRTC component is loaded in the browser session

The environment is affected if the installed Firefox version is below 115.33.0, or between 128.0 and 140.7.x, or below 148.0; OR the installed Thunderbird version is below 140.8.0 or below 148.0, AND WebRTC audio/video processing is in use.

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 115.33.0 / 140.8.0 / 148.0 or later
Fixed in 115.33.0140.8.0148.0
Interim mitigation

Apply the vendor-supplied patches by upgrading to Firefox 148, Firefox ESR 115.33/140.8, or Thunderbird 148/140.8 as appropriate for the affected deployment.

Recommended fix High confidence

Firefox 148 / Firefox ESR 115.33 / Firefox ESR 140.8 / Thunderbird 148 / Thunderbird 140.8 (depending on product and channel in use)

  1. 1. Check current Firefox version by navigating to menu > Help > About Firefox
  2. 2. Check current Thunderbird version by navigating to menu > Help > About Thunderbird
  3. 3. For Firefox: Download and install Firefox 148 or later from www.mozilla.org/firefox/
  4. 4. For Firefox ESR: If using ESR channel, upgrade to Firefox ESR 115.33 or later, or Firefox ESR 140.8 or later
  5. 5. For Thunderbird: Download and install Thunderbird 148 or later from www.mozilla.org/thunderbird/
  6. 6. For Thunderbird ESR: Upgrade to Thunderbird 140.8 or later
  7. 7. Restart the application after upgrade
  8. 8. Verify the version number matches or exceeds the fixed releases
Caveat Major version upgrades (e.g., 115.x to 148.x) may include feature changes; review release notes for compatibility with existing extensions or configurations

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
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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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-2026-2757 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