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FirefoxWeb browser · Mozilla

CVE-2023-5174

CRITICAL · 9.8 CVSS v3.1 Published 2023-09-27
Fix available
A fix is available. Upgrade to 115.3 / 118 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
If Windows failed to duplicate a handle during process creation, the sandbox code may have inadvertently freed a pointer twice, resulting in a use-after-free and a potentially exploitable crash. *This bug only affects Firefox on Windows when run in non-standard configurations (such as using `runas`). Other operating systems are unaffected.* This vulnerability affects Firefox < 118, Firefox ESR < 115.3, and Thunderbird < 115.3.

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

Use-after-free vulnerability in Firefox/Thunderbird sandbox code on Windows. When Windows fails to duplicate a handle during process creation, the code inadvertently frees a pointer twice, leading to a use-after-free condition. Only affects Windows in non-standard configurations (such as using 'runas').

MitigationUpdate affected software to Firefox 118, Firefox ESR 115.3, or Thunderbird 115.3 or later. No configuration changes required.

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:< 118
Firefox EsrWeb browser
Affected:< 115.3
ThunderbirdApplication
Affected:< 115.3

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. Verify Windows platform
    Confirm the operating system is Windows. This vulnerability only affects Windows environments.
    Affected if The system is NOT running Windows - if Linux or macOS, this CVE does not apply.
  2. Check Firefox version
    Open Firefox, go to Help > About Firefox, or navigate to about:support, to view the installed version number.
    Affected if The installed Firefox version is less than 118 (or less than 115.3 for Firefox ESR).
  3. Check Thunderbird version
    Open Thunderbird, go to Help > About Thunderbird, or navigate to about:support, to view the installed version number.
    Affected if The installed Thunderbird version is less than 115.3.
  4. Identify non-standard launch configurations
    Review how Firefox or Thunderbird is being launched. Check for use of Windows 'runas' command, scheduled tasks with alternate credentials, or scripts that invoke the browser with different user contexts.
    Affected if The application is being launched via 'runas' or other methods that create a new user context/process, which triggers the vulnerable code path.

A user is affected if running Windows with Firefox versions below 118 (or ESR below 115.3) or Thunderbird below 115.3, AND the application is launched using non-standard configurations like 'runas' that trigger the handle duplication failure path.

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 115.3 / 118 or later
Fixed in 115.3118
Interim mitigation

Update affected software to Firefox 118, Firefox ESR 115.3, or Thunderbird 115.3 or later. No configuration changes required.

Recommended fix High confidence

Firefox 118 / Firefox ESR 115.3 / Thunderbird 115.3

  1. For Firefox users: Upgrade to Firefox 118 or later
  2. For Firefox ESR users: Upgrade to Firefox ESR 115.3 or later
  3. For Thunderbird users: Upgrade to Thunderbird 115.3 or later
  4. On Windows, ensure the upgrade is applied even when running in non-standard configurations (such as using `runas`)
Caveat None expected - these are minor version updates within the same major release train containing only security fixes

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-2023-5174 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