FKIE_CVE-2021-4477
Vulnerability from fkie_nvd - Published: 2026-04-03 23:17 - Updated: 2026-07-24 22:10
Severity
Summary
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.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"product": "Hirschmann HiLCOS OpenBAT",
"vendor": "Belden",
"versions": [
{
"status": "affected",
"version": "3.80-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "8.90-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.00-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.00-RU1",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.10-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU1",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU2",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU3",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU4",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU5",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU6",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU7",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU8",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.12-RU9",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.13-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "9.13-RU1",
"versionType": "custom"
},
{
"status": "affected",
"version": "10.12-REL",
"versionType": "custom"
},
{
"status": "affected",
"version": "10.12-RU1",
"versionType": "custom"
},
{
"status": "unaffected",
"version": "10.12-RU2",
"versionType": "custom"
}
]
}
],
"source": "disclosure@vulncheck.com"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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."
},
{
"lang": "es",
"value": "Los productos Hirschmann HiLCOS OpenBAT y BAT450 contienen una vulnerabilidad de omisi\u00f3n de cortafuegos en implementaciones IPv6 IPsec que permite que el tr\u00e1fico de las conexiones VPN omita las reglas de cortafuegos configuradas. Los atacantes pueden explotar esta vulnerabilidad al establecer conexiones IPv6 IPsec (IKEv1 o IKEv2) mientras utilizan simult\u00e1neamente una conexi\u00f3n a Internet IPv6 para eludir la aplicaci\u00f3n de la pol\u00edtica del cortafuegos."
}
],
"id": "CVE-2021-4477",
"lastModified": "2026-07-24T22:10:00.140",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "NONE",
"baseScore": 9.1,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 5.2,
"source": "disclosure@vulncheck.com",
"type": "Secondary"
}
],
"cvssMetricV40": [
{
"cvssData": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"availabilityRequirement": "NOT_DEFINED",
"baseScore": 9.3,
"baseSeverity": "CRITICAL",
"confidentialityRequirement": "NOT_DEFINED",
"exploitMaturity": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"source": "disclosure@vulncheck.com",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2021-4477",
"options": [
{
"exploitation": "none"
},
{
"automatable": "yes"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-04-06T13:16:56.315497Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-04-03T23:17:01.043",
"references": [
{
"source": "disclosure@vulncheck.com",
"url": "https://assets.belden.com/m/5fd1a50fa50cb252/original/Belden-Security-Bulletin-BSECV-1v0-2019-09.pdf"
},
{
"source": "disclosure@vulncheck.com",
"url": "https://www.vulncheck.com/advisories/hirschmann-hilcos-openbat-bat450-ipv6-ipsec-firewall-bypass"
}
],
"sourceIdentifier": "disclosure@vulncheck.com",
"vulnStatus": "Awaiting Analysis",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-284"
}
],
"source": "disclosure@vulncheck.com",
"type": "Secondary"
}
]
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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