What is CVE-2021-27734?

CVE-2021-27734 is a critical-severity vulnerability in Belden Hirschmann Hios, classified under Improper Authentication. CVSS score: 9.8/10. Published 2021-05-17.

How severe is CVE-2021-27734?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Auth bypass in Belden Hirschmann Hios

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.

Vulnerability class: Broken Authentication

Published 2021-05-17 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.013 (69.3th percentile), scored 2026-10-20.

Low probability of exploitation in the next 30 days, but still tracked. 69th percentile — 69.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.013 · newest: 0.013 · change: 0.000

Affected products

Belden Hirschmann Hios — versions 07.1.01, 07.1.02
Belden Hisecos

Weakness classification (CWE)

CWE-287 — Improper Authentication

References

dam.belden.com/dmm3bwsv3/assetstream.aspx (Vendor Advisory)

Frequently asked questions

What is CVE-2021-27734?: CVE-2021-27734 is a critical-severity vulnerability in Belden Hirschmann Hios, classified under Improper Authentication. CVSS score: 9.8/10. Published 2021-05-17.
How severe is CVE-2021-27734?: Critical severity. CVSS v3 base score is 9.8 out of 10.