dbcve.org
FirefoxWeb browser · Mozilla

CVE-2025-1009

CRITICAL · 9.8 CVSS v3.1 Published 2025-02-04
Fix available
A fix is available. Upgrade to 115.20.0 / 128.7.0 or later.
See remediation →
100/100
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
An attacker could have caused a use-after-free via crafted XSLT data, leading to a potentially exploitable crash. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

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

A use-after-free vulnerability exists in Firefox and Thunderbird's XSLT processing code. An attacker can trigger this by providing crafted XSLT data, causing the browser to access memory after it has been freed, leading to a potentially exploitable crash that could allow arbitrary code execution.

MitigationUpgrade to Firefox 135, Firefox ESR 128.7, or Thunderbird 128.7/135. Alternatively, disable XSLT processing in browser settings or avoid untrusted XSLT content until updates are applied.

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:< 115.20.0< 135.0>= 128.1.0, < 128.7.0
ThunderbirdApplication
Affected:>= 128.0.1, < 128.7.0>= 131.0, < 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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/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. Identify installed product and version
    In Firefox: Go to Help > About Firefox. In Thunderbird: Go to Help > About Thunderbird. Note the exact version number displayed.
    Affected if Version is Firefox < 115.20.0, Firefox < 135.0 but >= 128.1.0, or Thunderbird >= 128.0.1 but < 128.7.0, or Thunderbird >= 131.0 but < 135.0
  2. Confirm XSLT processing is accessible
    Check if the browser has the ability to process XSLT stylesheets. This is a built-in capability enabled by default in both Firefox and Thunderbird - no explicit configuration toggle exists in standard settings.
    Affected if XSLT processing is available in the application (default state)
  3. Check for XSLT content handling
    Review browser profiles or email attachments for any .xsl or .xslt files, or websites that may load XSLT stylesheets. In Thunderbird, examine any imported or received XSLT-related content.
    Affected if Untrusted or crafted XSLT content can be processed by the application

You are affected if your Firefox version is below 115.20.0, below 135.0 but at or above 128.1.0, or your Thunderbird version is between 128.0.1 and 128.7.0 or between 131.0 and 135.0, and XSLT content can be processed by your installation.

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 115.20.0 / 128.7.0 / 135.0 or later
Fixed in 115.20.0128.7.0135.0
Interim mitigation

Upgrade to Firefox 135, Firefox ESR 128.7, or Thunderbird 128.7/135. Alternatively, disable XSLT processing in browser settings or avoid untrusted XSLT content until updates are applied.

Recommended fix High confidence

Firefox 135.0+ (rapid), Firefox ESR 115.20+, Firefox ESR 128.7+, Thunderbird 128.7+, or Thunderbird 135.0+

  1. Identify the currently installed Firefox or Thunderbird version via Help > About (or running 'firefox --version' or 'thunderbird --version' in the command line)
  2. For Firefox: If using the rapid release channel, upgrade to Firefox 135.0 or later
  3. For Firefox ESR: If using Firefox ESR 115.x, upgrade to 115.20 or later; if using Firefox ESR 128.x, upgrade to 128.7 or later
  4. For Thunderbird: If using Thunderbird 128.x, upgrade to 128.7 or later; if using Thunderbird 131.x-134.x, upgrade to 135.0 or later
  5. Restart the application after upgrade completes
  6. Verify the version has been updated to a fixed release

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2025-1009 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2025-1009 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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