Critical 9.1Published Apr 3, 2026

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

Updated under an hour ago (Oct 27, 2026, 6:00 AM ET)

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It affects Belden Hirschmann HiLCOS OpenBAT. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for Belden Hirschmann HiLCOS OpenBAT

Exploited in the last 30 days

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: 9.1 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness (CWE): CWE-284
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: VulnCheck
NVD analysis: Awaiting Analysis
Record last updated: Apr 6, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Belden Hirschmann HiLCOS OpenBAT belden:hirschmann_hilcos_openbat (from the name)	3.80-REL; 8.90-REL; 9.00-REL; 9.00-RU1; 9.10-REL; 9.12-REL; 9.12-RU1; 9.12-RU2; and 12 more ranges	CNA record

References

References

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

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.