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FirefoxWeb browser · Mozilla

CVE-2025-8040

HIGH · 8.8 CVSS v3.1 Published 2025-07-22
Fix available
A fix is available. Upgrade to 140.1 / 141.0 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
Memory safety bugs present in Firefox ESR 140.0, Thunderbird ESR 140.0, Firefox 140 and Thunderbird 140. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 141, Firefox ESR 140.1, Thunderbird 141, 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

Memory safety bugs in Firefox 140 and Thunderbird 140 (including ESR variants) allowed memory corruption that could potentially be exploited for arbitrary code execution.

MitigationUpgrade to Firefox 141, Firefox ESR 140.1, Thunderbird 141, or Thunderbird 140.1.

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:< 140.1< 141.0
ThunderbirdApplication
Affected:< 140.1< 141.0

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. Identify installed Mozilla product
    Check if Firefox or Thunderbird is installed. On Windows, look in Program Files or Program Files (x86). On macOS, check /Applications. On Linux, check package manager or /usr/lib/firefox or /usr/lib/thunderbird.
    Affected if Neither Firefox nor Thunderbird is installed (not affected)
  2. Determine Firefox version
    In Firefox, go to Help > About Firefox, or type 'about:support' in the address bar, or run 'firefox --version' from command line.
    Affected if Version is less than 140.1 or between 140.x and 141.0 (excluding 141.0)
  3. Determine Thunderbird version
    In Thunderbird, go to Help > About Thunderbird, or run 'thunderbird --version' from command line.
    Affected if Version is less than 140.1 or between 140.x and 141.0 (excluding 141.0)
  4. Check ESR variant versions
    If using Firefox ESR or Thunderbird ESR, the version will include 'ESR' label. Check Help > About for the exact version number.
    Affected if ESR version is below 140.1

Affected if Firefox or Thunderbird (including ESR variants) version is 140.x (any patch level below 140.1) or any version below 141.0.

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 140.1 / 141.0 or later
Fixed in 140.1141.0
Interim mitigation

Upgrade to Firefox 141, Firefox ESR 140.1, Thunderbird 141, or Thunderbird 140.1.

Recommended fix High confidence

Firefox 141, Firefox ESR 140.1, Thunderbird 141, or Thunderbird 140.1 (depending on your release channel)

  1. Check current Firefox version by clicking Help > About Firefox, or current Thunderbird version by clicking Help > About Thunderbird
  2. If version is below 140.1 or 141.0, navigate to https://www.mozilla.org/firefox/all/ or https://www.mozilla.org/thunderbird/all/
  3. Download the appropriate installer for your operating system
  4. Run the installer and follow the prompts to complete the upgrade
  5. After installation, verify the version by checking Help > About again to confirm version 141 or ESR 140.1 is installed
Caveat None expected - this is a security maintenance release with bug fixes; user data and settings are preserved during upgrade

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
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

Scan for this in your stack

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dbcve dependency scanner

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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-2025-8040 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