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FirefoxWeb browser · Mozilla

CVE-2026-8957

HIGH · 8.8 CVSS v3.1 Published 2026-05-19
Fix available
A fix is available. Upgrade to 140.11 / 140.11.0 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

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
Privilege escalation in the Enterprise Policies component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

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 privilege escalation vulnerability exists in the Enterprise Policies component of Firefox and Thunderbird. This component allows administrators to enforce organizational policies across deployments. The vulnerability allows an attacker to elevate their privileges beyond what should be permitted, potentially bypassing intended policy restrictions.

MitigationApply the vendor-supplied patches by updating to Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11 or later. Verify that Enterprise Policies configurations remain functional after updating.

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:< 140.11.0< 151.0.0
ThunderbirdApplication
Affected:< 140.11< 151.0.0

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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. Determine Firefox or Thunderbird installed version
    For Firefox: Open Help > About Firefox, or run 'firefox --version' from command line. For Thunderbird: Open Help > About Thunderbird, or run 'thunderbird --version' from command line.
    Affected if The installed version is below 140.11.0 OR between 140.11.0 and 151.0.0 (not inclusive of 151.0.0)
  2. Verify Enterprise Policies feature is in use
    Check for the presence of policies.json configuration file. On Windows this is typically in the distribution directory or program files. On Linux it may be in /etc/firefox/policies or ~/.mozilla/policies. On macOS check /Library/Application Support/Mozilla/Policy or within the app bundle.
    Affected if A policies.json file exists and contains policy definitions (indicating Enterprise Policies are being applied)
  3. Confirm policy enforcement is active
    In Firefox or Thunderbird, navigate to about:policies to view the currently active policies. This page shows whether policies are being enforced.
    Affected if The about:policies page shows policies as 'active' or displays organizational policy configurations

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 140.11 / 140.11.0 / 151.0.0 or later
Fixed in 140.11140.11.0151.0.0
Interim mitigation

Apply the vendor-supplied patches by updating to Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11 or later. Verify that Enterprise Policies configurations remain functional after updating.

Recommended fix High confidence

Firefox ESR 140.11+ / Firefox 151+ / Thunderbird 140.11+ / Thunderbird 151+

  1. Identify the current installed version of Firefox or Thunderbird
  2. For Firefox ESR users: Upgrade to Firefox ESR 140.11 or later
  3. For Firefox regular users: Upgrade to Firefox 151 or later
  4. For Thunderbird ESR users: Upgrade to Thunderbird 140.11 or later
  5. For Thunderbird regular users: Upgrade to Thunderbird 151 or later
  6. Restart the application after upgrade to ensure the fix is fully applied
  7. Verify the installed version matches or exceeds the fixed release

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.

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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-2026-8957 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