CVE-2021-4477
CRITICALCVSS v3
9.1
CRITICAL
EPSS Score
—
exploit probability
CISA KEV
No
known exploited
Exploitation
—
SSVC status
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.
Technical Details
- CVSS v3 Vector
- 3.1
- Published
- 4/3/2026
- Last Modified
- 4/7/2026
Frequently Asked Questions
What is CVE-2021-4477?
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.
Is CVE-2021-4477 actively exploited?
Active exploitation of CVE-2021-4477 has not been confirmed. The EPSS score is N/A%, indicating the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2021-4477?
CVE-2021-4477 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string 3.1.
Is CVE-2021-4477 affecting your environment?
Use isMalicious to check if any of your IPs or domains are associated with this vulnerability's IOCs.