CVE-2021-43399

Name: CVE-2021-43399
Creator: NVD / NIST
Published: 2021-12-08T19:15:10.02+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 1.37%

Last modified Jun 17, 2026

CVE-2021-43399 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. The Yubico YubiHSM YubiHSM2 library 2021.08, included in the yubihsm-shell project, does not properly validate the length of some operations including SSH signing requests, and some data operations received from a YubiHSM 2 device.. EPSS estimates a 1.37% chance of exploitation in the next 30 days.

Description

The Yubico YubiHSM YubiHSM2 library 2021.08, included in the yubihsm-shell project, does not properly validate the length of some operations including SSH signing requests, and some data operations received from a YubiHSM 2 device.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

1.37%

68.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Yubico	Yubihsm 2 Software Development Kit	<= 2021.08

References

https://blog.inhq.net/posts/yubico-yubihsm-shell-vuln3/Exploit, Third Party Advisory
https://www.yubico.com/support/security-advisories/ysa-2021-04/Vendor Advisory
https://blog.inhq.net/posts/yubico-yubihsm-shell-vuln3/Exploit, Third Party Advisory
https://www.yubico.com/support/security-advisories/ysa-2021-04/Vendor Advisory

Timeline

Published: Dec 8, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-43399?

How severe is CVE-2021-43399?

CVE-2021-43399 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.37% probability of exploitation in the next 30 days.

How do I fix CVE-2021-43399?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-43399?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST