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FirefoxWeb browser · Mozilla

CVE-2026-16371

HIGH · 8.8 CVSS v3.1 Published 2026-07-21
Fix available
A fix is available. Upgrade to 140.13.0 / 153.0 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges 4 weeks old

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 DOM: Navigation component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

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 in the DOM Navigation component allows attackers to elevate their privileges, likely through malicious manipulation of the DOM in a way that bypasses security restrictions.

MitigationUpdate affected browsers to Firefox 153+, Firefox ESR 140.13+, Thunderbird 153+, or Thunderbird 140.13+ to remediate this 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:< 140.13.0< 153.0.0
ThunderbirdApplication
Affected:< 140.13.0>= 141.0, < 153.0

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. Check Firefox version
    Navigate to Firefox, click the menu (three lines), select Help, then About Firefox. Alternatively, enter 'about:support' in the address bar and locate the Version field.
    Affected if The installed version is less than 140.13.0, or is between 140.13.0 and 153.0.0 (exclusive). Versions 153.0.0 and later are not affected.
  2. Check Thunderbird version
    Navigate to Thunderbird, click the menu (three lines), select Help, then About Thunderbird. Alternatively, enter 'about:support' in the address bar and locate the Version field.
    Affected if The installed version is less than 140.13.0, or is between 141.0.0 and 153.0.0 (exclusive). Versions 140.13.0 through 141.0.0 are likely not affected. Versions 153.0.0 and later are not affected.
  3. Confirm DOM Navigation component usage
    This vulnerability resides in the DOM Navigation component. No specific configuration check is required since DOM Navigation is a core browser feature. The vulnerability is triggered when processing certain navigation-related DOM elements.
    Affected if The vulnerability is present in the affected version ranges regardless of specific user configuration, as it is a flaw in the navigation component itself.

A user is affected if they are running Mozilla Firefox or Thunderbird at a version lower than 140.13.0, or at a version between 141.0.0 and 152.x (inclusive) for Thunderbird (Firefox is affected at any version below 153.0.0).

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 140.13.0 / 153.0 / 153.0.0 or later
Fixed in 140.13.0153.0153.0.0
Interim mitigation

Update affected browsers to Firefox 153+, Firefox ESR 140.13+, Thunderbird 153+, or Thunderbird 140.13+ to remediate this vulnerability.

Recommended fix High confidence

Firefox 153, Firefox ESR 140.13, Thunderbird 153, Thunderbird 140.13

  1. Identify the currently installed Firefox, Firefox ESR, or Thunderbird version by navigating to Help > About (or the application menu)
  2. For Firefox: If the version is below 153, download and install Firefox 153 from the official Mozilla website
  3. For Firefox ESR: If the version is below 140.13, download and install Firefox ESR 140.13 from the official Mozilla website
  4. For Thunderbird: If the version is below 153, download and install Thunderbird 153 from the official Mozilla website
  5. For Thunderbird ESR: If the version is below 140.13, download and install Thunderbird 140.13 from the official Mozilla website
  6. Restart the application after upgrading
  7. Verify the new version is installed by checking Help > About
Caveat No major breaking changes expected for standard users; users of older extensions or custom configurations should verify compatibility

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.

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-2026-16371 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