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FirefoxWeb browser · Mozilla

CVE-2025-8031

CRITICAL · 9.8 CVSS v3.1 Published 2025-07-22
Fix available
A fix is available. Upgrade to 128.13.0 / 140.1.0 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
The `username:password` part was not correctly stripped from URLs in CSP reports potentially leaking HTTP Basic Authentication credentials. This vulnerability was fixed in Firefox 141, Firefox ESR 128.13, Firefox ESR 140.1, Thunderbird 141, Thunderbird 128.13, and Thunderbird 140.1.

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

The username:password portion of URLs was not correctly stripped from Content Security Policy (CSP) violation reports, potentially exposing HTTP Basic Authentication credentials when users visited websites that triggered CSP violations. This credential leak occurred in the report generation mechanism.

MitigationUpdate affected software to patched versions: Firefox 141, Firefox ESR 128.13/140.1, or Thunderbird 141/128.13/140.1 to remove credentials from CSP reports.

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:< 128.13.0< 141.0>= 140.0, < 140.1.0
ThunderbirdApplication
Affected:< 128.13.0< 141.0>= 140.0, < 140.1.0

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
    Open Firefox and navigate to Help > About Firefox, or enter 'about:support' in the address bar. Locate the 'Version' field.
    Affected if Version is below 128.13.0, OR between 140.0 and 140.0.x (where x is any build before 140.1.0), OR below 141.0 (all versions below 141.0 are affected except 128.13.0-140.0)
  2. Check installed Thunderbird version
    Open Thunderbird and navigate to Help > About Thunderbird. Locate the 'Version' field.
    Affected if Version is below 128.13.0, OR between 140.0 and 140.0.x (where x is any build before 140.1.0), OR below 141.0 (all versions below 141.0 are affected except 128.13.0-140.0)
  3. Verify CSP report-uri directive is configured
    Inspect HTTP response headers from your web applications for 'Content-Security-Policy' headers containing 'report-uri' or 'report-to' directives. These directives instruct the browser to send violation reports to a specified endpoint.
    Affected if A CSP policy with a report-uri or report-to endpoint is active - this is the configuration that enables the vulnerable reporting mechanism
  4. Review CSP violation reports for authentication data
    If you have access to CSP violation report endpoints or logs, examine any violation reports for URLs that may contain username:password@ in the URL format (HTTP Basic Authentication).
    Affected if Any CSP violation reports contain URLs with credentials in the format http://username:password@hostname or https://username:password@hostname

You are affected if you run Firefox or Thunderbird versions below 128.13.0 or between 140.0 and 140.0.x, AND you have CSP report-uri or report-to configured, which would cause credential-containing URLs to be sent in violation reports.

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 128.13.0 / 140.1.0 / 141.0 or later
Fixed in 128.13.0140.1.0141.0
Interim mitigation

Update affected software to patched versions: Firefox 141, Firefox ESR 128.13/140.1, or Thunderbird 141/128.13/140.1 to remove credentials from CSP reports.

Recommended fix High confidence

Firefox 141.0 or later (or Firefox ESR 128.13+ / ESR 140.1+); Thunderbird 141.0 or later (or Thunderbird ESR 128.13+ / ESR 140.1+)

  1. 1. Open Firefox or Thunderbird
  2. 2. Navigate to the Help menu (or click the menu button)
  3. 3. Select 'About Firefox' or 'About Thunderbird'
  4. 4. The application will check for and automatically download the latest update
  5. 5. Click 'Restart to update Firefox/Thunderbird' once the update is ready
  6. 6. Alternatively, download the specific version directly from the official Mozilla website: https://www.mozilla.org/

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing0.5 h
  • Review / QA0.5 h
3.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

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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-2025-8031 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