No exploitation reportedFix available

CVE-2021-27734

Q: Is CVE-2021-27734 actively exploited?

Active exploitation of CVE-2021-27734 has not been confirmed. Its EPSS score was 1.3% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-27734?

CVE-2021-27734 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2021-05-17
Fixed in08.6.00
WeaknessCWE-287

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

Hirschmann HiOS 07.1.01, 07.1.02, and 08.1.00 through 08.5.xx and HiSecOS 03.3.00 through 03.5.01 allow remote attackers to change the credentials of existing users.

Timeline

dates in UTC

2021-05-1715:15CVE 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-2021-27734?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-27734?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Belden hirschmann hios

Branch	Affected	Fixed in	Source
8.x	≥ 08.1.00, < 08.6.00	08.6.00	NVD
7.1	= 07.1.01	no fix published	NVD
7.1	= 07.1.02	no fix published	NVD

Belden hisecos

Branch	Affected	Fixed in	Source
3.x	≥ 03.3.00, ≤ 03.5.01	no fix published	NVD

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

Fix

Update Belden hirschmann hios to 08.6.00

Advisories and patches

dam.belden.comVendor Advisory

Detection

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

Sources

NVDCVSS 3.19.8read 2026-10-23
NVDCVSS 2.07.5read 2026-10-23
NVDweakness (CWE)CWE-287read 2026-10-23
FIRST EPSSEPSS score1.3 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2021-05-17
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-27734?

Hirschmann HiOS 07.1.01, 07.1.02, and 08.1.00 through 08.5.xx and HiSecOS 03.3.00 through 03.5.01 allow remote attackers to change the credentials of existing users.

Is CVE-2021-27734 actively exploited?

Active exploitation of CVE-2021-27734 has not been confirmed. Its EPSS score was 1.3% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-27734?

CVE-2021-27734 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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