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.

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact High

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploitation none

Automatable yes

Technical Impact total

Affected Vendors & Products

Vendors Products
Belden
  • Hirschmann Hilcos Openbat

No data.

No data.

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

Tue, 07 Apr 2026 00:00:00 +0000

Type Values Removed Values Added
First Time appeared Belden
Belden hirschmann Hilcos Openbat
Vendors & Products Belden
Belden hirschmann Hilcos Openbat

Mon, 06 Apr 2026 14:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Fri, 03 Apr 2026 22:45:00 +0000

Type Values Removed Values Added
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.
Title Hirschmann HiLCOS OpenBAT BAT450 IPv6 IPsec Firewall Bypass
Weaknesses CWE-284
References
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}

cvssV4_0

{'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'}
cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published: 2026-04-03T22:37:45.879Z

Updated: 2026-04-06T13:17:07.744Z

Reserved: 2026-04-03T16:46:37.018Z

Link: CVE-2021-4477

cve-icon Vulnrichment

Updated: 2026-04-06T13:17:02.444Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-04-03T23:17:01.043

Modified: 2026-04-07T13:20:55.200

Link: CVE-2021-4477

cve-icon Redhat

No data.