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FirefoxWeb browser · Mozilla

CVE-2025-10537

HIGH · 8.8 CVSS v3.1 Published 2025-09-16
Fix available
A fix is available. Upgrade to 140.3.0 / 143.0 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 140.2, Thunderbird ESR 140.2, Firefox 142 and Thunderbird 142. 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 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3.

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 142 and ESR 140.2, and Thunderbird 142 and ESR 140.2, could allow arbitrary code execution through memory corruption. The vulnerabilities were fixed in Firefox 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3.

MitigationUpdate all affected Firefox installations to version 143 or ESR 140.3+, and Thunderbird to version 143 or 140.3+ to patch the memory corruption vulnerabilities.

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:< 140.3.0< 143.0
ThunderbirdApplication
Affected:< 140.3.0< 143.0

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 Firefox version
    Run 'firefox --version' in terminal, or open Firefox and go to Help > About Firefox to view the version number
    Affected if Version is below 140.3.0 OR between 140.3.0 and 142.x (anything below 143.0)
  2. Identify installed Thunderbird version
    Run 'thunderbird --version' in terminal, or open Thunderbird and go to Help > About Thunderbird to view the version number
    Affected if Version is below 140.3.0 OR between 140.3.0 and 142.x (anything below 143.0)
  3. Check for Firefox ESR release
    If using Firefox ESR, run 'firefox --version' and note if the version string contains 'ESR'. ESR versions 140.2 and below are affected; 140.3+ is fixed
    Affected if Firefox ESR version is below 140.3.0
  4. Check for Thunderbird ESR release
    If using Thunderbird ESR, run 'thunderbird --version' and note if the version string contains 'ESR'. ESR versions 140.2 and below are affected; 140.3+ is fixed
    Affected if Thunderbird ESR version is below 140.3.0

You are affected if any installed Firefox or Thunderbird version is below 140.3.0 or is any version from 140.3.x through 142.x (the fix versions are 143.0 and 140.3.0 or higher).

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 140.3.0 / 143.0 or later
Fixed in 140.3.0143.0
Interim mitigation

Update all affected Firefox installations to version 143 or ESR 140.3+, and Thunderbird to version 143 or 140.3+ to patch the memory corruption vulnerabilities.

Recommended fix High confidence

Firefox 143 (or Firefox ESR 140.3), Thunderbird 143 (or Thunderbird 140.3)

  1. Check the current version of Firefox or Thunderbird by clicking the menu button and selecting 'Help' > 'About Firefox' or 'About Thunderbird'
  2. Download the appropriate fixed version: Firefox 143, Firefox ESR 140.3, Thunderbird 143, or Thunderbird 140.3 from the official Mozilla website (www.mozilla.org)
  3. Close all instances of the browser or email client
  4. Run the installer and follow the prompts to complete the update
  5. Restart Firefox or Thunderbird after the update completes
  6. Verify the version by checking 'Help' > 'About' to confirm the installed version matches the fixed release
Caveat Standard Mozilla release updates typically maintain user settings and extensions; however, some older extensions may need updates for compatibility with version 143

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,424.

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-2025-10537 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