CVE-2026-100724
http4k before 6.49.0.0 Host Header Routing Bypass via reverseProxy
- State
- Published
- Severity
- 6.3 Medium
- Published
- Sep 27, 2026
- Updated
- Oct 29, 2026
- Reserved
- Sep 26, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 6.3 Medium | 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 | VulnCheck |
| 3.1 | 5.4 Medium | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N | VulnCheck |
Weaknesses
- CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Affected Products
| Product | Versions |
|---|---|
http4khttp4k |
|
http4khttp4k |
|
http4khttp4k |
|
References
- GitHub Security Advisory (GHSA-jrpc-7vxp-69p6)vendor-advisory
- Patch Commitpatch
- Patch Commitpatch
- VulnCheck Advisory: http4k before 6.49.0.0 Host Header Routing Bypass via reverseProxythird-party-advisory
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