FirefoxWeb browser · Mozilla
CVE-2018-5174
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 · uneditedIn the Windows 10 April 2018 Update, Windows Defender SmartScreen honors the "SEE_MASK_FLAG_NO_UI" flag associated with downloaded files and will not show any UI. Files that are unknown and potentially dangerous will be allowed to run because SmartScreen will not prompt the user for a decision, and if the user is offline all files will be allowed to be opened because Windows won't prompt the user to ask what to do. Firefox incorrectly sets this flag when downloading files, leading to less secure behavior from SmartScreen. Note: this issue only affects Windows 10 users running the April 2018 update or later. It does not affect other Windows users or other operating systems. This vulnerability affects Thunderbird < 52.8, Thunderbird ESR < 52.8, Firefox < 60, and Firefox ESR < 52.8.
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 · high confidenceFirefox incorrectly sets the SEE_MASK_FLAG_NO_UI flag when downloading files on Windows 10 April 2018 Update or later, causing Windows Defender SmartScreen to skip security UI warnings for unknown or potentially dangerous files. This allows malicious downloaded files to execute without user prompts, and when offline, all files bypass SmartScreen checks entirely.
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
< 52.8.0< 60.0< 52.8.0< 52.8.0CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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 checksWork through these to decide whether this CVE applies to you.
-
Verify Windows 10 versionOpen Settings > System > About and check the Windows version. The April 2018 Update corresponds to build 1803 or later. Alternatively, run 'winver' from the command prompt.Affected if Windows 10 build is 1803 or later and the installed Firefox/Thunderbird version is below the fixed versions
-
Check installed Firefox versionOpen Firefox, go to Help > About Firefox, or navigate to the installation directory and check the version file. On Windows, this is typically in C:\Program Files\Mozilla Firefox\firefox.exe properties, or run 'firefox --version' from command line if available.Affected if Firefox version is earlier than 52.8.0 or between 52.8.0 and 59.x (i.e., < 60.0)
-
Check installed Thunderbird versionOpen Thunderbird, go to Help > About Thunderbird, or check the application properties in the installation directory. On Windows, this is typically in C:\Program Files\Mozilla Thunderbird\thunderbird.exe.Affected if Thunderbird version is earlier than 52.8.0
-
Confirm download functionality is in useVerify that the affected application has been used to download files, or check browser/download settings to confirm downloads are enabled. The vulnerability specifically affects downloaded files, so downloads must be occurring for exploitation.Affected if Downloads are performed using the affected application on a vulnerable Windows 10 system
The environment is affected if running Windows 10 build 1803 or later with Firefox version < 60.0 (or < 52.8.0), or Thunderbird version < 52.8.0, and files are downloaded using the application.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor data52.8.060.0
Upgrade to Firefox 60+, Firefox ESR 52.8+, Thunderbird 52.8+ on Windows 10 systems with the April 2018 Update or later to ensure the flag is properly handled and SmartScreen warnings display correctly.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
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 locallyCheck whether your project pulls in CVE-2018-5174 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2018-5174 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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.
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.
- 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