CVE-2018-5174 [High] | Security Vulnerability in Firefox

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.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-11-21	0.69%	0.54%	-0.15%
2	2025-11-18	0.54%	0.69%	+0.15%
3	2025-05-12	—	0.54%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-11-21

0.69%

0.54%

-0.15%

2025-11-18

0.54%

0.69%

+0.15%

2025-05-12

—

0.54%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.5	3.0	HIGH	`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	3.9	3.6	[email protected]
5.0	2.0	MEDIUM	`AV:N/AC:L/Au:N/C:N/I:P/A:N` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:N) No availability impact.	10.0	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.5

3.0

HIGH

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

3.9

3.6

[email protected]

5.0

2.0

MEDIUM

AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:N): No availability impact.

10.0

2.9

[email protected]

OS Trackers for CVE-2018-5174

vendor	priority	summary	link
`debian`	unimportant	CVE-2018-5174 unimportant priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11.	https://security-tracker.debian.org/tracker/CVE-2018-5174
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2018-5174
`ubuntu`	medium	CVE-2018-5174 medium priority: Ubuntu including 2 source packages (firefox, thunderbird), 10 status rows across 5 suites (artful, bionic, trusty, upstream, xenial): not-affected 6, DNE 2, released 2.	https://ubuntu.com/security/CVE-2018-5174

Affected software / configurations for CVE-2018-5174

Vendor	Product	Version	Raw CPE
mozilla	firefox	< 52.8.0	cpe:2.3:a:mozilla:firefox::::::::
mozilla	firefox	< 60.0	cpe:2.3:a:mozilla:firefox::::::::
mozilla	thunderbird	< 52.8.0	cpe:2.3:a:mozilla:thunderbird::::::::
mozilla	thunderbird_esr	< 52.8.0	cpe:2.3:a:mozilla:thunderbird_esr::::::::

References for CVE-2018-5174

URL	Tags
http://www.securityfocus.com/bid/104136	Third Party Advisory VDB Entry
http://www.securitytracker.com/id/1040896	Third Party Advisory VDB Entry
https://bugzilla.mozilla.org/show_bug.cgi?id=1447080	Issue 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

URL

CVE-2018-5174

Exploit prediction scoring system (EPSS) score for CVE-2018-5174

Common vulnerability scoring system (CVSS) metrics for CVE-2018-5174

Weakness enumeration for CVE-2018-5174

OS Trackers for CVE-2018-5174

Affected software / configurations for CVE-2018-5174

References for CVE-2018-5174