Medium 5.4Published Sep 27, 2026

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

Updated under an hour ago (2026-10-19 07:50 UTC)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 5.4 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
Weakness (CWE): CWE-444
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: VulnCheck
NVD analysis: Deferred
Record last updated: Sep 30, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

http4k http4k http4k:http4k (from the name)	before 6.49.0.0; 6.49.0.0 not affected	CNA record

References

https://github.com/http4k/http4k/security/advisories/GHSA-jrpc-7vxp-69p6vendor-advisory
https://github.com/http4k/http4k/commit/0121b05537patch
https://github.com/http4k/http4k/commit/54c6385615patch
https://www.vulncheck.com/advisories/http4k-before-6.49.0.0-host-header-routing-bypass-via-reverseproxythird-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.