CVE-2018-5174
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.81%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
In 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.
- CVSS 3.0
- 7.5 HIGHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 1.81% probability · 78th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- mozilla/firefox · mozilla/thunderbird · mozilla/thunderbird esr
- Source
- security@mozilla.org
EPSS 1.8% since 27 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- http://www.securityfocus.com/bid/104136Third Party Advisory, VDB Entry
- http://www.securitytracker.com/id/1040896Third Party Advisory, VDB Entry
- https://bugzilla.mozilla.org/show_bug.cgi?id=1447080Issue Tracking, Permissions Required, Third Party Advisory
- https://www.mozilla.org/security/advisories/mfsa2018-11/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2018-12/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2018-13/Vendor Advisory
- http://www.securityfocus.com/bid/104136Third Party Advisory, VDB Entry
- http://www.securitytracker.com/id/1040896Third Party Advisory, VDB Entry
- https://bugzilla.mozilla.org/show_bug.cgi?id=1447080Issue Tracking, Permissions Required, Third Party Advisory
- https://www.mozilla.org/security/advisories/mfsa2018-11/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2018-12/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2018-13/Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.