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FirefoxWeb browser · Mozilla

CVE-2021-38510

HIGH · 8.8 CVSS v3.1 Published 2021-12-08
Fix available
A fix is available. Upgrade to 91.3.0 / 94.0 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

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
The executable file warning was not presented when downloading .inetloc files, which, due to a flaw in Mac OS, can run commands on a user's computer.*Note: This issue only affected Mac OS operating systems. Other operating systems are unaffected.*. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

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

Firefox and Thunderbird failed to display the executable file warning when downloading .inetloc files on Mac OS. These files can contain embedded AppleScript commands that execute automatically due to a Mac OS flaw, allowing arbitrary code execution without user warning.

MitigationUpgrade to Firefox 94+, Thunderbird 91.3+, or Firefox ESR 91.3+ to receive the proper executable file warning before downloading .inetloc files.

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:< 94.0
Firefox EsrWeb browser
Affected:< 91.3.0
ThunderbirdApplication
Affected:< 91.3.0

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 product
    Check for Firefox, Firefox ESR, or Thunderbird in /Applications folder on Mac, or run 'ls /Applications | grep -i firefox' and 'ls /Applications | grep -i thunderbird'
    Affected if No Mozilla product installed means not affected by this specific vulnerability
  2. Determine Firefox version
    Run 'defaults read /Applications/Firefox.app/Contents/Info CFBundleVersion' or open Firefox, go to Help > About Firefox
    Affected if Version less than 94.0 on standard Firefox indicates vulnerability on Mac OS
  3. Determine Firefox ESR version
    Run 'defaults read /Applications/Firefox.app/Contents/Info CFBundleVersion' - ESR versions contain 'ESR' in the update channel. Check Help > About Firefox for 'ESR' designation
    Affected if Version less than 91.3.0 on Firefox ESR indicates vulnerability on Mac OS
  4. Determine Thunderbird version
    Run 'defaults read /Applications/Thunderbird.app/Contents/Info CFBundleVersion' or open Thunderbird, go to Help > About Thunderbird
    Affected if Version less than 91.3.0 on Thunderbird indicates vulnerability on Mac OS
  5. Confirm operating system is Mac OS
    Run 'uname -s' which should return 'Darwin', or check System Preferences > About
    Affected if This vulnerability only affects Mac OS environments - Windows/Linux users are not impacted by this specific flaw

User is affected if running Firefox < 94.0, Firefox ESR < 91.3.0, or Thunderbird < 91.3.0 on Mac OS, where .inetloc files can be downloaded and executed without warning.

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 91.3.0 / 94.0 or later
Fixed in 91.3.094.0
Interim mitigation

Upgrade to Firefox 94+, Thunderbird 91.3+, or Firefox ESR 91.3+ to receive the proper executable file warning before downloading .inetloc files.

Recommended fix High confidence

Firefox 94.0, Firefox ESR 91.3.0, or Thunderbird 91.3.0

  1. Identify which Mozilla product is in use (Firefox, Firefox ESR, or Thunderbird)
  2. Check current version via: Help > About Firefox/Thunderbird
  3. For Firefox: Upgrade to version 94.0 or later
  4. For Firefox ESR: Upgrade to version 91.3.0 or later
  5. For Thunderbird: Upgrade to version 91.3.0 or later
  6. Restart the application after upgrade

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,090
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.

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-2021-38510 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