CVE-2018-20340 [Medium] | Memory Corruption in Libu2f-Host

Yubico libu2f-host 1.1.6 contains unchecked buffers in devs.c, which could enable a malicious token to exploit a buffer overflow. An attacker could use this to attempt to execute malicious code using a crafted USB device masquerading as a security token on a computer where the affected library is currently in use. It is not possible to perform this attack with a genuine YubiKey.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.20%	0.50%	+0.30%
2	2025-12-04	0.13%	0.20%	+0.07%
3	2025-03-30	—	0.13%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.20%

0.50%

+0.30%

2025-12-04

0.13%

0.20%

+0.07%

2025-03-30

—

0.13%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.8	3.0	MEDIUM	`CVSS:3.0/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:P) Hands-on access—USB, keyboard, opening the case—not something you do purely over the wire. 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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	0.9	5.9	[email protected]
4.6	2.0	MEDIUM	`AV:L/AC:L/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:L) Requires local access to the target system. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	3.9	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.8

3.0

MEDIUM

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

Attack vector (AV:P): Hands-on access—USB, keyboard, opening the case—not something you do purely over the wire.
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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

0.9

5.9

[email protected]

4.6

2.0

MEDIUM

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

Access vector (AV:L): Requires local access to the target system.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

3.9

6.4

[email protected]

OS Trackers for CVE-2018-20340

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2018-20340 not yet assigned priority: Debian including 1 source packages (libu2f-host), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2018-20340
`gentoo`	high	CVE-2018-20340: 1 GLSA(s) (202004-15), 1 atom(s) (app-crypt/libu2f-host); latest impact high.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2018-20340
`suse`	medium	CVE-2018-20340 severity moderate: SUSE including 24 source package names (libu2f-host-devel-1.1.10-150600.16.3, libu2f-host-devel-1.1.10-3.9.1, …), 49 product×package rows across 21 product lines (SUSE Linux Enterprise Desktop 12 SP4, SUSE Linux Enterprise High Performance Computing 12 SP5, … (21 product lines)): Fixed 49.	https://www.suse.com/security/cve/CVE-2018-20340/
`ubuntu`	medium	CVE-2018-20340 medium priority: Ubuntu including 1 source packages (libu2f-host), 19 status rows across 19 suites (bionic, cosmic, disco, eoan, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 14, released 2, DNE 1, needed 1, pending 1.	https://ubuntu.com/security/CVE-2018-20340

Affected software / configurations for CVE-2018-20340

Vendor	Product	Version	Raw CPE
yubico	libu2f-host	1.1.6	cpe:2.3:a:yubico:libu2f-host:1.1.6:::::::*
debian	debian_linux	9.0	cpe:2.3:o:debian:debian_linux:9.0:::::::*

References for CVE-2018-20340

URL	Tags
https://blog.inhq.net/posts/yubico-libu2f-host-vuln-part1/
https://developers.yubico.com/libu2f-host/Release_Notes.html	Release Notes Vendor Advisory
https://seclists.org/bugtraq/2019/Feb/23	Mailing List Third Party Advisory
https://security.gentoo.org/glsa/202004-15
https://www.debian.org/security/2019/dsa-4389	Third Party Advisory
https://www.yubico.com/support/security-advisories/ysa-2019-01/	Patch Vendor Advisory

URL

CVE-2018-20340

Exploit prediction scoring system (EPSS) score for CVE-2018-20340

Common vulnerability scoring system (CVSS) metrics for CVE-2018-20340

Weakness enumeration for CVE-2018-20340

OS Trackers for CVE-2018-20340

Affected software / configurations for CVE-2018-20340

References for CVE-2018-20340