CVE-2021-4477

CRITICAL EPSS 23.6%

Published Apr 3, 20262mo ago · Modified Jun 17, 20261w ago

9.3 CVSS 4.0

Critical

Published Apr 3, 2026 2mo ago

Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score

9.3

Exploitability

—

Impact

—

Vector string

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector Network

Attack Complexity Low

Privileges Required None

User Interaction None

Scope X

Threat Intelligence

EPSS Exploit Probability

23.6% percentile

Exploit & Patch Status

No Known Exploit

No Patch Available

Weaknesses 1

CWE-284

References 2

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

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.