CVE-2021-4477 CRITICAL

CVE-2021-4477: Hirschmann HiLCOS OpenBAT BAT450 IPv6 IPsec Firewall Bypass

Vendor Belden
Product Hirschmann HiLCOS OpenBAT
Weakness CWE-284
Published April 3, 2026
Last update April 6, 2026
View on NVD All CVEs

CVSS base score

9.3/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality —
Integrity —

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

April 3, 2026 CVE published
April 6, 2026 Record updated