Vulnerability · Published Sep 27, 2026 · Assigned by VulnCheck
CVE-2026-100724http4k before 6.49.0.0 Host Header Routing Bypass via reverseProxy
Medium 5.4
In plain English
A medium-severity security flaw in http4k from http4k. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 28% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Maven | org.http4k:http4k-core | 6.49.0.0 | GHSA-jrpc-7vxp-69p6 |
| Maven | org.http4k:http4k-core | 5.42.0.0 | GHSA-jrpc-7vxp-69p6 |
| Maven | org.http4k:http4k-core | 4.51.0.0 | GHSA-jrpc-7vxp-69p6 |
Affected products (as reported)
Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
References
- GitHub Security Advisory (GHSA-jrpc-7vxp-69p6) vendor-advisory
- Patch Commit patch
- Patch Commit patch
- VulnCheck Advisory: http4k before 6.49.0.0 Host Header Routing Bypass via reverseProxy third-party-advisory