CVE-2021-4477: Belden Hirschmann Hilcos Openbat

Critical severity, CVSS 9.1. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Belden Hirschmann Hilcos Openbat: version 3.80-REL only; version 8.90-REL only; version 9.00-REL only; version 9.00-RU1 only; version 9.10-REL only; version 9.12-REL only; …

Published 2026-04-03. Last modified 2026-07-24.