CVE-2026-100724
Full vulnerability record from the local CVENow database.
Description
http4k (Maven package org.http4k:http4k-core) before 6.49.0.0, 5.42.0.0 and 4.51.0.0 uses substring (Contains) matching on the Host header by default in reverseProxy() and reverseProxyRouting() when dispatching to configured virtual hosts. If these functions are deployed as a public-facing inbound HTTP handler with two or more configured virtual hosts, a remote attacker can supply a Host header that merely contains a configured vhost name (for example Host: admin.evil.com for a vhost configured as "admin") and be routed to that vhost, bypassing routing-based authorization. The intended outbound-dispatch and test-time uses, where the Host value is set by the calling application, are not affected.
Severity
MEDIUM
CVSS score
6.3
(v4.0)
Vulnerability status
Deferred
Source identifier
Published
2026-09-27 02:17:20.603000
Last modified
2026-10-29 21:17:06.847000
View original CVE JSON
{
"id": "CVE-2026-100724",
"sourceIdentifier": "[email protected]",
"published": "2026-09-27T02:17:20.603",
"lastModified": "2026-10-29T21:17:06.847",
"vulnStatus": "Deferred",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "http4k (Maven package org.http4k:http4k-core) before 6.49.0.0, 5.42.0.0 and 4.51.0.0 uses substring (Contains) matching on the Host header by default in reverseProxy() and reverseProxyRouting() when dispatching to configured virtual hosts. If these functions are deployed as a public-facing inbound HTTP handler with two or more configured virtual hosts, a remote attacker can supply a Host header that merely contains a configured vhost name (for example Host: admin.evil.com for a vhost configured as \"admin\") and be routed to that vhost, bypassing routing-based authorization. The intended outbound-dispatch and test-time uses, where the Host value is set by the calling application, are not affected."
}
],
"affected": [
{
"source": "[email protected]",
"affectedData": [
{
"vendor": "http4k",
"product": "http4k",
"defaultStatus": "unaffected",
"packageURL": "pkg:maven/org.http4k/http4k-core",
"versions": [
{
"version": "6.0.0.0",
"lessThan": "6.49.0.0",
"versionType": "custom",
"status": "affected"
},
{
"version": "6.49.0.0",
"versionType": "custom",
"status": "unaffected"
}
]
},
{
"vendor": "http4k",
"product": "http4k",
"defaultStatus": "unaffected",
"packageURL": "pkg:maven/org.http4k/http4k-core",
"versions": [
{
"version": "5.0.0.0",
"lessThan": "5.42.0.0",
"versionType": "custom",
"status": "affected"
},
{
"version": "5.42.0.0",
"versionType": "custom",
"status": "unaffected"
}
]
},
{
"vendor": "http4k",
"product": "http4k",
"defaultStatus": "unaffected",
"packageURL": "pkg:maven/org.http4k/http4k-core",
"versions": [
{
"version": "0",
"lessThan": "4.51.0.0",
"versionType": "custom",
"status": "affected"
},
{
"version": "4.51.0.0",
"versionType": "custom",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {
"cvssMetricV40": [
{
"source": "[email protected]",
"type": "Secondary",
"cvssData": {
"version": "4.0",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/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",
"baseScore": 6.3,
"baseSeverity": "MEDIUM",
"attackVector": "NETWORK",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"privilegesRequired": "NONE",
"userInteraction": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "NONE",
"vulnAvailabilityImpact": "NONE",
"subConfidentialityImpact": "LOW",
"subIntegrityImpact": "LOW",
"subAvailabilityImpact": "NONE",
"exploitMaturity": "NOT_DEFINED",
"confidentialityRequirement": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"availabilityRequirement": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"valueDensity": "NOT_DEFINED",
"vulnerabilityResponseEffort": "NOT_DEFINED",
"providerUrgency": "NOT_DEFINED"
}
}
],
"cvssMetricV31": [
{
"source": "[email protected]",
"type": "Secondary",
"cvssData": {
"version": "3.1",
"vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N",
"baseScore": 5.4,
"baseSeverity": "MEDIUM",
"attackVector": "NETWORK",
"attackComplexity": "HIGH",
"privilegesRequired": "NONE",
"userInteraction": "NONE",
"scope": "CHANGED",
"confidentialityImpact": "LOW",
"integrityImpact": "LOW",
"availabilityImpact": "NONE"
},
"exploitabilityScore": 2.2,
"impactScore": 2.7
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-09-30T15:15:13.800731Z",
"id": "CVE-2026-100724",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "partial"
}
],
"role": "CISA Coordinator",
"version": "2.0.3"
}
}
]
},
"weaknesses": [
{
"source": "[email protected]",
"type": "Secondary",
"description": [
{
"lang": "en",
"value": "CWE-444"
}
]
}
],
"references": [
{
"url": "https://github.com/http4k/http4k/commit/0121b05537",
"source": "[email protected]"
},
{
"url": "https://github.com/http4k/http4k/commit/54c6385615",
"source": "[email protected]"
},
{
"url": "https://github.com/http4k/http4k/security/advisories/GHSA-jrpc-7vxp-69p6",
"source": "[email protected]"
},
{
"url": "https://www.vulncheck.com/advisories/http4k-before-6.49.0.0-host-header-routing-bypass-via-reverseproxy",
"source": "[email protected]"
}
]
}