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CVE-2026-100724— http4k before 6.49.0.0 Host Header Routing Bypass via reverseProxy

Quick assessment

Affected
http4k http4k
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

http4k（Maven 包 org.http4k:http4k-core）在 6.49.0.0、5.42.0.0 和 4.51.0.0 之前的版本中，默认在 reverseProxy() 和 reverseProxyRouting() 方法中对 Host 头使用子串（Contains）匹配机制来分发请求至已配置的虚拟主机。如果这些函数被部署为面向公众的入站 HTTP 处理程序，并配置了两个或多个虚拟主机，则远程攻击者可以提供一个仅包含某个已配置虚拟主机名称的 Host 头（例如，对于配置为 “admin” 的虚拟

CVSS 5.4 · Medium EPSS 0.34% · P25
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I. Basic Information for CVE-2026-100724

Vulnerability Information
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Vulnerability Title
http4k before 6.49.0.0 Host Header Routing Bypass via reverseProxy
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
http4k http4k 0 ~ 6.49.0.0 -
http4k http4k 0 ~ 5.42.0.0 -
http4k http4k 0 ~ 4.51.0.0 -

II. Public POCs for CVE-2026-100724

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III. Intelligence Information for CVE-2026-100724

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Vendor Advisories for CVE-2026-100724 (1)

Other References for CVE-2026-100724 (3)

Same Patch Batch · http4k · 2026-09-27 · 3 CVEs total

CVE-2026-100725 6.5 MEDIUM http4k before 6.48.0.0 Cookie Scoping Bypass via BasicCookieStorage
CVE-2026-100834 5.9 MEDIUM http4k before 6.48.0.0 Digest Authentication Replay Protection Bypass

IV. Related Vulnerabilities

Same product: http4k
Same vendor: http4k
Same weakness: CWE-444

V. Comments for CVE-2026-100724

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