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FirefoxWeb browser · Mozilla

CVE-2025-1931

HIGH · 7.5 CVSS v3.1 Published 2025-03-04
Fix available
A fix is available. Upgrade to 115.21.0 / 128.8.0 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
It was possible to cause a use-after-free in the content process side of a WebTransport connection, leading to a potentially exploitable crash. This vulnerability was fixed in Firefox 136, Firefox ESR 115.21, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.

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 · high confidence

Use-after-free vulnerability in the content process side of WebTransport connections in Firefox and Thunderbird that could lead to potentially exploitable crashes. Fixed in versions Firefox 136, Firefox ESR 115.21/128.8, and Thunderbird 136/128.8.

MitigationUpdate affected Mozilla products (Firefox and Thunderbird) to the fixed versions or later to remediate the use-after-free vulnerability.

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:< 115.21.0< 136.0>= 116.0, < 128.8.0
ThunderbirdApplication
Affected:< 128.8.0>= 129.0, < 136.0

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 the installed Mozilla product
    Determine whether Firefox or Thunderbird is installed. On Linux, check /usr/bin/firefox or /usr/bin/thunderbird. On Windows, look in Program Files for Mozilla Firefox or Mozilla Thunderbird. On macOS, check /Applications/Firefox.app or /Applications/Thunderbird.app.
    Affected if The product is Firefox or Thunderbird and the version falls within the affected ranges below
  2. Get the Firefox version number
    In Firefox, navigate to Menu > Help > About Firefox. The version number is displayed on this page.
    Affected if Version is less than 115.21.0, OR between 116.0 (inclusive) and 128.8.0 (exclusive), OR less than 136.0 (with 136.0 being the main release fix)
  3. Get the Thunderbird version number
    In Thunderbird, navigate to Menu > Help > About Thunderbird. The version number is displayed on this page.
    Affected if Version is less than 128.8.0, OR between 129.0 (inclusive) and 136.0 (exclusive)
  4. Verify WebTransport is enabled
    In Firefox address bar, type about:config and press Enter. Search for the preference network.webtransport.enabled. In Thunderbird, go to Edit > Preferences > Advanced > Config Editor, search for network.webtransport.enabled.
    Affected if The preference network.webtransport.enabled is set to true (vulnerability requires WebTransport to be enabled)
  5. Confirm client-side WebTransport usage
    Review browser extensions, visited websites, or enterprise policies that may trigger WebTransport connections. Check Network logs (DevTools > Network tab) for WebTransport traffic patterns.
    Affected if The browser actively uses or is configured to accept WebTransport connections

You are affected if you run Firefox or Thunderbird with a version below the fixed releases (136.0 for Firefox main, 128.8.0 for ESR/Thunderbird, or 115.21.0 for older ESR) AND have WebTransport enabled and actively used.

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 115.21.0 / 128.8.0 / 136.0 or later
Fixed in 115.21.0128.8.0136.0
Interim mitigation

Update affected Mozilla products (Firefox and Thunderbird) to the fixed versions or later to remediate the use-after-free vulnerability.

Recommended fix High confidence

Firefox 136.0 / Firefox ESR 128.8 / Firefox ESR 115.21 / Thunderbird 128.8 / Thunderbird 136.0

  1. Identify the currently installed Firefox or Thunderbird version from the application menu (Help > About Firefox/Thunderbird)
  2. Download the appropriate fixed version from the official Mozilla website: https://www.mozilla.org/
  3. For Firefox users: Upgrade to Firefox 136.0 or later, or Firefox ESR 128.8 or later, or Firefox ESR 115.21 or later
  4. For Thunderbird users: Upgrade to Thunderbird 128.8 or later, or Thunderbird 136.0 or later
  5. Restart the application after upgrading
  6. Verify the installed version matches or exceeds the fixed release
Caveat Security updates typically have minimal breaking changes; however, always review release notes for your specific version before upgrading 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
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.

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-2025-1931 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