CVE-2021-4477Network attack vector

Firewall bypass via IPv6 IPsec policy failure

Published Apr 3, 2026 · Updated Apr 3, 2026

Firewall bypass in Belden HiLCOS OpenBAT and BAT450 before 10.12-RU2 allows remote attackers to send VPN traffic past configured rules. When IPv6 IPsec using IKEv1 or IKEv2 and an IPv6 Internet connection operate simultaneously, the firewall path fails to enforce its configured policy on VPN traffic. Exploitation requires that dual IPv6 configuration and can expose protected devices or networks to unwanted traffic without causing a reported service interruption.

CVSS severity9.3
Critical
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Firewall bypass in Belden HiLCOS OpenBAT and BAT450 before 10.12-RU2 allows remote attackers to send VPN traffic past configured rules. When IPv6 IPsec using IKEv1 or IKEv2 and an IPv6 Internet connection operate simultaneously, the firewall path fails to enforce its configured policy on VPN traffic. Exploitation requires that dual IPv6 configuration and can expose protected devices or networks to unwanted traffic without causing a reported service interruption.

The record

CVE
CVE-2021-4477
Published
Apr 3, 2026
Updated
Apr 3, 2026
Vendor
Belden
Product
Hirschmann HiLCOS WLAN Software
Classifications
CWE-284, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.12-REL
  2. Affected versionversion=10.12-RU1
  3. Affected versionversion=3.80-REL
  4. Affected versionversion=8.90-REL
  5. Affected versionversion=9.00-REL
  6. Affected versionversion=9.00-RU1
  7. Affected versionversion=9.10-REL
  8. Affected versionversion=9.12-REL
  9. Affected versionversion=9.12-RU1
  10. Affected versionversion=9.12-RU2
  11. Affected versionversion=9.12-RU3
  12. Affected versionversion=9.12-RU4
  13. Affected versionversion=9.12-RU5
  14. Affected versionversion=9.12-RU6
  15. Affected versionversion=9.12-RU7
  16. Affected versionversion=9.12-RU8
  17. Affected versionversion=9.12-RU9
  18. Affected versionversion=9.13-REL
  19. Affected versionversion=9.13-RU1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Belden · Hirschmann HiLCOS WLAN Softwareversion=10.12-REL; version=10.12-RU1; version=3.80-REL; version=8.90-REL; version=9.00-REL; version=9.00-RU1; version=9.10-REL; version=9.12-REL; version=9.12-RU1; version=9.12-RU2; version=9.12-RU3; version=9.12-RU4; version=9.12-RU5; version=9.12-RU6; version=9.12-RU7; version=9.12-RU8; version=9.12-RU9; version=9.13-REL; version=9.13-RU1

Published CVSS scores

9.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
9.1VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-284Improper Access Control
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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