Security readout for executives and security teams
Plain-English summary
This flaw can let traffic from IPv6 IPsec VPN connections bypass firewall rules on affected Hirschmann HiLCOS OpenBAT/BAT450 deployments. For organizations using these industrial networking devices, the business concern is loss of expected network segmentation and policy enforcement.
Executive priority
Treat as high-priority for industrial or remote-access networks using these devices with IPv6 IPsec. The key risk is trusted VPN traffic bypassing intended firewall controls, potentially undermining segmentation and access policy.
Technical view
CVE-2021-4477 is a CWE-284 improper access control issue in IPv6 IPsec deployments. An unauthenticated network attacker can establish IPv6 IPsec connections using IKEv1 or IKEv2 while also using IPv6 Internet connectivity to circumvent configured firewall policy enforcement. CVSS v4.0 score is 9.3.
Likely exposure
Exposure is most likely where affected Hirschmann HiLCOS OpenBAT/BAT450 devices run listed HiLCOS versions and are configured for IPv6 IPsec VPN service with IPv6 Internet connectivity. Organizations not using IPv6 IPsec on these devices may have lower practical exposure.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation evidence. The issue is still serious because it is network-reachable, requires no privileges or user interaction, and affects firewall enforcement in VPN-connected environments.
Researcher notes
Affected versions are listed for Hirschmann HiLCOS OpenBAT from 3.80-REL through 10.12-RU2 in the source bundle. Default status is marked unaffected outside listed versions. Patch details are not included in the provided text, so rely on Belden guidance.
Mitigation direction
- Identify affected Hirschmann HiLCOS OpenBAT/BAT450 devices and firmware versions.
- Review the Belden security bulletin for vendor-approved fixes or workarounds.
- Prioritize remediation for devices using IPv6 IPsec VPN connectivity.
- Review whether IPv6 IPsec is required on affected deployments.
- Apply compensating network controls according to vendor and operational guidance.
Validation and detection
- Inventory Hirschmann HiLCOS OpenBAT/BAT450 assets and firmware versions.
- Check whether IPv6 IPsec VPN using IKEv1 or IKEv2 is enabled.
- Confirm whether affected devices also have IPv6 Internet connectivity.
- Review firewall policy assumptions for VPN-originated IPv6 traffic.
- Monitor vendor advisories and vulnerability feeds for updated remediation details.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-284: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-4477 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.3 (4.0)
- Known Exploited
- No
- Published
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
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
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——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
9.3CriticalVector: 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
Source materials
- CVE List V5 sourceCVE List V5
- https://assets.belden.com/m/5fd1a50fa50cb252/original/Belden-Security-Bulletin-BSECV-1v0-2019-09.pdfCVE reference · vendor-advisory
- https://www.vulncheck.com/advisories/hirschmann-hilcos-openbat-bat450-ipv6-ipsec-firewall-bypassCVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Access Control
Improper Access Control represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.