Is CVE-2021-4477 actively exploited?

No active exploitation of CVE-2021-4477 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-4477 be exploited remotely?

Yes. CVE-2021-4477 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-4477?

CVE-2021-4477 has a CVSS score of 9.1 (CRITICAL).

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CRITICAL

CVE-2021-4477

CWE-284Published: April 3, 2026· Updated: Apr 7, 2026

9.1

CVSS v3.1

EPSS:0.01%probability of exploitation in 30 daysPercentile:0.3th

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.

NVD Source

Technical Analysis

CVE-2021-4477 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), with a CVSS base score of 9.1.