{"cve":"CVE-2026-100724","nvd":{"published":"2026-09-27T02:17:20.603","modified":"2026-09-30T17:32:07.107","status":"Deferred","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.","cvss_v4":{"vector":"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","score":6.3},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N","score":5.4},"cwes":["CWE-444"],"references":["https://github.com/http4k/http4k/commit/0121b05537","https://github.com/http4k/http4k/commit/54c6385615","https://github.com/http4k/http4k/security/advisories/GHSA-jrpc-7vxp-69p6","https://www.vulncheck.com/advisories/http4k-before-6.49.0.0-host-header-routing-bypass-via-reverseproxy"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:56:48.555445741+00:00"},"epss":{"cve":"CVE-2026-100724","score":0.00344,"percentile":0.27648,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-jrpc-7vxp-69p6","url":"https://osv.dev/vulnerability/GHSA-jrpc-7vxp-69p6","summary":"http4k: `reverseProxy()` defaulted to substring (`Contains`) matching on `Host`; tightened to `Exact`","modified":"2026-09-27T11:56:07.608749487Z","packages":[{"ecosystem":"Maven","name":"org.http4k:http4k-core","purl":"pkg:maven/org.http4k/http4k-core","ranges":[">=6.0.0.0 <6.49.0.0"],"fixed":["6.49.0.0"]},{"ecosystem":"Maven","name":"org.http4k:http4k-core","purl":"pkg:maven/org.http4k/http4k-core","ranges":[">=5.0.0.0 <5.42.0.0"],"fixed":["5.42.0.0"]},{"ecosystem":"Maven","name":"org.http4k:http4k-core","purl":"pkg:maven/org.http4k/http4k-core","ranges":["<4.51.0.0"],"fixed":["4.51.0.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}