What is CVE-2021-4477?

CVE-2021-4477 is a critical-severity vulnerability in Belden Hirschmann Hilcos Openbat, classified under Improper Access Control. CVSS score: 9.1/10. Published 2026-04-03.

How severe is CVE-2021-4477?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in Belden Hirschmann Hilcos Openbat

CVE-2021-4477

Hirschmann HiLCOS OpenBAT and BAT450 products contain a firewall bypass vulnerability in IPv6 IPsec deployments that allows traffic from VPN connections to bypass configured firewall rules. Attackers can exploit this vulnerability by establishing IPv6 IPsec connections (IKEv1 or IKEv2) while simultaneously using an IPv6 Internet connection to circumvent firewall policy enforcement.

EPSS: 0.003 (24.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

Affected products

Belden Hirschmann Hilcos Openbat — versions 3.80-REL, 8.90-REL, 9.00-REL

Weakness classification (CWE)

CWE-284 — Improper Access Control

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com

Frequently asked questions

What is CVE-2021-4477?: CVE-2021-4477 is a critical-severity vulnerability in Belden Hirschmann Hilcos Openbat, classified under Improper Access Control. CVSS score: 9.1/10. Published 2026-04-03.
How severe is CVE-2021-4477?: Critical severity. CVSS v3 base score is 9.1 out of 10.