Vulnerability · Published Apr 3, 2026 · Assigned by VulnCheck

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

Critical 9.1

In plain English

A critical-severity improper access control in Hirschmann HiLCOS OpenBAT from Belden. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities).

Severity (CVSS 3.1)9.1Critical

Exploit odds (30 days)0.3%top 73.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 (as reported)

Vendor	Product	Versions
Belden	Hirschmann HiLCOS OpenBAT	3.80-REL8.90-REL9.00-REL9.00-RU19.10-REL9.12-REL9.12-RU19.12-RU2

Weakness: CWE-284 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

In plain English

Official description

Affected products (as reported)

References