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FirefoxWeb browser · Mozilla

CVE-2025-5268

HIGH · 8.1 CVSS v3.1 Published 2025-05-27
Fix available
A fix is available. Upgrade to 128.11.0 / 139.0 or later.
See remediation →
90/100
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
Memory safety bugs present in Firefox 138, Thunderbird 138, Firefox ESR 128.10, and Thunderbird 128.10. 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 139, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.

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 · high confidence

Multiple memory safety bugs in Firefox 138 and Thunderbird 138 (and ESR 128.10 variants) that could lead to memory corruption and potentially allow arbitrary code execution. The exact vulnerability type and affected component are not specified in the advisory.

MitigationUpgrade affected installations to Firefox 139, Firefox ESR 128.11, Thunderbird 139, or Thunderbird 128.11.

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:< 128.11.0< 139.0
ThunderbirdApplication
Affected:< 128.11.0>= 129.0, < 139.0

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/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 run 'firefox --version' from command line
    Affected if Version is below 128.11.0 OR version is 138.x/139.x but below 139.0
  2. Check installed Thunderbird version
    Open Thunderbird and navigate to 'Help' > 'About Thunderbird', or run 'thunderbird --version' from command line
    Affected if Version is below 128.11.0 OR version is 129.x through 138.x (any version below 139.0)
  3. Verify Firefox ESR version if applicable
    If using the ESR (Extended Support Release) channel, check version via 'Help' > 'About Firefox' - ESR versions display 'ESR' in the version string
    Affected if ESR version is 128.10 or earlier (below 128.11.0)

Your environment is affected if Firefox or Thunderbird is installed with any version lower than 128.11.0, or any version from 129.0 through 138.x (for Thunderbird) or 138.x (for Firefox) that is below 139.0.

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 128.11.0 / 139.0 or later
Fixed in 128.11.0139.0
Interim mitigation

Upgrade affected installations to Firefox 139, Firefox ESR 128.11, Thunderbird 139, or Thunderbird 128.11.

Recommended fix High confidence

Firefox 139.0, Firefox ESR 128.11.0, Thunderbird 139.0, or Thunderbird ESR 128.11.0 (depending on product and channel)

  1. 1. Check the currently installed Firefox version by navigating to Menu > Help > About Firefox (or typing 'about:support' in the address bar)
  2. 2. Check the currently installed Thunderbird version by navigating to Menu > Help > About Thunderbird (or typing 'about:support' in the address bar)
  3. 3. For Firefox: Download Firefox 139.0 (or later) from the official Mozilla website (www.mozilla.org) or use the built-in update mechanism (Menu > Help > Check for Updates)
  4. 4. For Thunderbird: Download Thunderbird 139.0 (or later) from the official Mozilla website (www.mozilla.org) or use the built-in update mechanism
  5. 5. If using Firefox ESR: Download Firefox ESR 128.11.0 (or later) from the Mozilla website
  6. 6. If using Thunderbird ESR: Download Thunderbird 128.11.0 (or later) from the Mozilla website
  7. 7. Install the updated version and restart the application
Caveat Standard major version upgrade; review release notes for any add-on compatibility changes or user preference changes

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,696.

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-2025-5268 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