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FirefoxWeb browser · Mozilla

CVE-2025-1938

MEDIUM · 6.5 CVSS v3.1 Published 2025-03-04
Fix available
A fix is available. Upgrade to 128.7.0 / 135.0 or later.
See remediation →
74/100
Remediation priority · Elevated
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 135, Thunderbird 135, Firefox ESR 128.7, and Thunderbird 128.7. 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 136, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.

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

Memory safety bugs in Firefox 135 and Thunderbird 135 (and ESR versions 128.7) caused memory corruption within the browser/email client rendering engine. These flaws could potentially be exploited to achieve arbitrary code execution through carefully crafted web content or email messages.

MitigationUpdate affected installations to Firefox 136, Firefox ESR 128.8, Thunderbird 136, or Thunderbird 128.8 to obtain the patched versions containing the memory safety fixes.

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:< 128.7.0< 135.0
ThunderbirdApplication
Affected:< 128.7.0>= 129.0, < 135.0

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
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

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
    In Firefox, go to Menu > Help > About Firefox, or navigate to about:support. The version number is displayed on this page.
    Affected if Version is below 135.0 (or below 128.7.0 for ESR branches)
  2. Check Thunderbird version
    In Thunderbird, go to Menu > Help > About Thunderbird. The version number is displayed on the dialog that opens.
    Affected if Version is below 128.7.0 OR version is 129.0 through 134.x
  3. Confirm active use of the rendering engine
    The vulnerability is triggered when the browser or email client renders untrusted web content or email messages. Check if the application processes HTML email or browses web pages.
    Affected if The application is used to render untrusted web pages or HTML email messages (this is the default use case for both applications)

If either Firefox is below version 135.0 (or below 128.7.0 for ESR) or Thunderbird is below 128.7.0 or between 129.0-134.x, and the application processes web content or email, the environment is affected.

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 128.7.0 / 135.0 or later
Fixed in 128.7.0135.0
Interim mitigation

Update affected installations to Firefox 136, Firefox ESR 128.8, Thunderbird 136, or Thunderbird 128.8 to obtain the patched versions containing the memory safety fixes.

Recommended fix High confidence

Firefox 136, Firefox ESR 128.8, Thunderbird 136, or Thunderbird 128.8 (depending on product and release branch)

  1. Back up your Firefox or Thunderbird profile data before upgrading (copy the profile folder to a safe location)
  2. Download the appropriate fixed version for your product: Firefox 136, Firefox ESR 128.8, Thunderbird 136, or Thunderbird 128.8
  3. Close all instances of Firefox or Thunderbird
  4. Install the downloaded version over your existing installation, or use the installer to update
  5. Restart the application and verify it launches successfully
  6. Optionally, clear the application cache after upgrade to ensure a clean state
Caveat Standard minor version upgrades typically have low risk; some older extensions may need updates for compatibility with Firefox/Thunderbird 136

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-2025-1938 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