CVE-2021-4477

Critical

Description

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.

SeverityCritical

CVSS9.1

Exploit probability—

ProductHirschmann HiLCOS OpenBAT

PublishedApr 3, 2026

First seenApr 3, 2026

Weakness typeCWE-284Improper access control

How to fix

Vendor advisories

assets.belden.com/m/5fd1a50fa50cb252/original/Belden-Security-Bulletin-BSECV-1v0-2019-09.pdf

Affected products

Product	Affected versions	Fixed in
Belden Hirschmann HiLCOS OpenBAT	3.80-REL, 8.90-REL, 9.00-REL, 9.00-RU1, 9.10-REL, 9.12-REL, 9.12-RU1, 9.12-RU2, 9.12-RU3, 9.12-RU4, 9.12-RU5, 9.12-RU6, 9.12-RU7, 9.12-RU8, 9.12-RU9, 9.13-REL, 9.13-RU1, 10.12-REL, 10.12-RU1	—

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