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CVE-2021-43399

24
FAUCET Score

CVE-2021-43399 affects the Yubico YubiHSM2 library (version 2021.08) within the yubihsm-shell project, stemming from insufficient validation of operation lengths, specifically for SSH signing and certain data operations from a YubiHSM 2 device. This vulnerability carries a CVSS score of 7.5 (High), indicating a network-based attack with low complexity that could lead to a denial of service. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
<= 2021.08CPE matchmatch criteria
cpe:2.3:a:yubico:yubihsm_2_software_development_kit:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.37%
Probability of exploitation in next 30 days
EPSS Percentile
69.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0137 is in the 49th percentile among its peer group of 51,485 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

blog.inhq.net / posts/yubico-yubihsm-shell-vuln3
ExploitThird Party Advisory
yubico.com / support/security-advisories/ysa-2021-04
Vendor Advisory