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FirefoxWeb browser · Mozilla

CVE-2025-2817

HIGH · 8.8 CVSS v3.1 Published 2025-04-29
Fix available
A fix is available. Upgrade to 115.23.0 / 128.10.0 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable 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
Thunderbird's update mechanism allowed a medium-integrity user process to interfere with the SYSTEM-level updater by manipulating the file-locking behavior. By injecting code into the user-privileged process, an attacker could bypass intended access controls, allowing SYSTEM-level file operations on paths controlled by a non-privileged user and enabling privilege escalation. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, and Thunderbird 128.10.

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

Thunderbird's update mechanism had a file-locking race condition where a medium-integrity user process could manipulate file lock behavior to interfere with the SYSTEM-level updater. An attacker with code injection capability into a user-privileged process could bypass intended access controls, allowing SYSTEM-level file operations on paths controlled by a non-privileged user, resulting in privilege escalation to SYSTEM.

MitigationApply security updates: Thunderbird 138 or 128.10, or Firefox ESR 115.23/128.10 if shared components are in use. Prioritize systems where users have medium-integrity access or where the application runs with elevated privileges.

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:< 115.23.0< 138.0>= 116.0, < 128.10.0
ThunderbirdApplication
Affected:< 128.10.0>= 129.0, < 138.0

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

CVSS:3.1/AV:N/AC:L/PR:L/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 Mozilla products
    Check for Firefox or Thunderbird installations on the system. On Windows, examine Program Files directories or use system inventory tools. On Linux, check package managers or /usr/lib directory for firefox or thunderbird directories.
    Affected if Either Firefox or Thunderbird is installed on the system
  2. Determine Firefox version
    For Firefox, locate the application and check its version. On Windows, this is typically in the file properties of firefox.exe or via Help > About Firefox. On Linux, run 'firefox --version' or check the package version.
    Affected if Firefox version is < 115.23.0, or >= 116.0 and < 128.10.0, or < 138.0 (note: these ranges overlap and collectively cover vulnerable versions)
  3. Determine Thunderbird version
    For Thunderbird, locate the application and check its version. On Windows, this is typically in the file properties of thunderbird.exe or via Help > About Thunderbird. On Linux, run 'thunderbird --version' or check the package version.
    Affected if Thunderbird version is < 128.10.0, or >= 129.0 and < 138.0
  4. Verify updater component presence
    Confirm the application's updater executable exists. For Firefox, look for updater.exe in the installation directory. For Thunderbird, look for updater.exe in the installation directory. This component handles the update process and is required for the vulnerability to be exploitable.
    Affected if The updater executable is present in the installation directory (this is the default configuration)

If either Firefox or Thunderbird is installed with a version falling within the affected ranges AND the updater component is present, the system is potentially affected by this vulnerability.

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 115.23.0 / 128.10.0 / 138.0 or later
Fixed in 115.23.0128.10.0138.0
Interim mitigation

Apply security updates: Thunderbird 138 or 128.10, or Firefox ESR 115.23/128.10 if shared components are in use. Prioritize systems where users have medium-integrity access or where the application runs with elevated privileges.

Recommended fix High confidence

Firefox 138 (stable), Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, or Thunderbird 128.10 - depending on current version branch

  1. 1. Determine current Firefox or Thunderbird version by navigating to Menu > Help > About (or using 'firefox --version' or 'thunderbird --version' in command line)
  2. 2. Identify which version branch you are currently on (115.x ESR, 116-137, 128.x ESR, or 129.x)
  3. 3. Download the appropriate fixed version from the official Mozilla website (www.mozilla.org) or your organization's software distribution channel
  4. 4. Close all browser/email client instances completely before upgrading
  5. 5. Run the installer for the fixed version (Firefox 138, Firefox ESR 128.10, Firefox ESR 115.23, Thunderbird 138, or Thunderbird 128.10 depending on your branch)
  6. 6. Follow the on-screen installation prompts
  7. 7. After installation, verify the version by checking Help > About to confirm the upgrade was successful
  8. 8. Restart the application and ensure all add-ons/plugins are functioning normally
Caveat Standard major version upgrades may include feature changes; review Mozilla release notes for any behavior changes relevant to your environment

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
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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-2025-2817 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