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.

References

https://www.vulncheck.com/advisories/hirschmann-hilcos-openbat-bat450-ipv6-ipsec-firewall-bypass

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

Details

Source: Mitre, NVD

Published: 2026-04-03

Updated: 2026-04-03

Risk Information

CVSS v2

Base Score: 9.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:N

Severity: High

CVSS v3

Base Score: 9.1

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Severity: Critical

CVSS v4

Base Score: 9.3

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

Severity: Critical

EPSS

EPSS: 0.00006