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

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-03 · updated 2026-07-24
Weakness: CWE-284

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.

Affected products

Belden Hirschmann HiLCOS OpenBAT: 3.80-REL, 8.90-REL, 9.00-REL, 9.00-RU1, 9.10-REL, 9.12-REL (+13)

References

https://assets.belden.com/m/5fd1a50fa50cb252/original/Belden-Security-Bulletin-BSECV-1v0-2019-09.pdf
https://www.vulncheck.com/advisories/hirschmann-hilcos-openbat-bat450-ipv6-ipsec-firewall-bypass

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