No exploitation reportedFix available

CVE-2021-28484

Q: Is CVE-2021-28484 actively exploited?

Active exploitation of CVE-2021-28484 has not been confirmed. Its EPSS score was 1.5% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-28484?

CVE-2021-28484 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-04-14
WeaknessCWE-835

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

An issue was discovered in the /api/connector endpoint handler in Yubico yubihsm-connector before 3.0.1 (in YubiHSM SDK before 2021.04). The handler did not validate the length of the request, which can lead to a state where yubihsm-connector becomes stuck in a loop waiting for the YubiHSM to send it data, preventing any further operations until the yubihsm-connector is restarted. An attacker can send 0, 1, or 2 bytes to trigger this.

Timeline

dates in UTC

2021-04-1418:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-28484?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-28484?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Fedoraproject fedora

Branch	Affected	Fixed in	Source
34.x	= 34	no fix published	NVD

Yubico yubihsm connector

Branch	Affected	Fixed in	Source
3.0	< 3.0.1	3.0.1	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

www.yubico.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
NVDweakness (CWE)CWE-835read 2026-10-23
FIRST EPSSEPSS score1.5 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-04-14
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-28484?

Is CVE-2021-28484 actively exploited?

Active exploitation of CVE-2021-28484 has not been confirmed. Its EPSS score was 1.5% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-28484?

CVE-2021-28484 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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