{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c 6.48.0.0"
      },
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4k:http4k-core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "6.0.0.0"
            },
            {
              "fixed": "6.49.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4k:http4k-core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.0.0.0"
            },
            {
              "fixed": "5.42.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.http4k:http4k-core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.51.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T21:15:59Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\n\n`reverseProxy()` and `reverseProxyRouting()` matched configured vhosts by substring on the `Host` header (`Contains` matcher) by default. The intended use of these functions in http4k is **outbound dispatch** (e.g. matching AWS service subdomains, per the `Contains` docstring) and **test-time composition** of fake backend networks. In either of those contexts the matched `Host` is set by the calling application, not by an external attacker, so the loose match has no exploit surface.\n\nIf, however, `reverseProxy()` was deployed as a public-facing inbound HTTP handler \u2014 which the function technically supports but is not the documented intent \u2014 an external attacker could send `Host: admin.evil.com` and reach a vhost configured as `admin`, bypassing routing-based authorization.\n\nThe `Contains` matcher\u0027s docstring explicitly documented this loose behaviour, but because `Contains` was the default, callers who never read the matcher docs would still get the loose behaviour.\n\n**Who is affected:** only deployments using `reverseProxy()` / `reverseProxyRouting()` as a public-facing inbound HTTP handler with two or more configured virtual hosts. The intended outbound / test-time usage is unaffected. If you *did* deploy `reverseProxy()` inbound and rely on multi-vhost routing for authorization, treat upgrade as urgent.\n\n### Patches\n\n| Line | Fixed in | Edition |\n|------|----------|---------|\n| v6.x (Community) | **6.49.0.0** | Community |\n| v5.x (LTS) | **5.42.0.0** | Enterprise \u2014 contact [enterprise@http4k.org](mailto:enterprise@http4k.org) (if `reverseProxy()` is present in your v5.x line) |\n| v4.x (LTS) | **4.51.0.0** | Enterprise \u2014 contact [enterprise@http4k.org](mailto:enterprise@http4k.org) (if `reverseProxy()` is present in your v4.x line) |\n\nThe fix changes the default matcher to `Exact`. Existing callers that genuinely need substring matching (e.g. AWS subdomain dispatch) must explicitly pass `matcher = Contains`.\n\n### Workarounds\n\nFor deployments that cannot upgrade immediately: wrap your `reverseProxy()` with a host-allow-list filter that requires an exact match against expected vhost names before delegating.",
  "id": "GHSA-jrpc-7vxp-69p6",
  "modified": "2026-06-19T21:15:59Z",
  "published": "2026-06-19T21:15:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/http4k/http4k/security/advisories/GHSA-jrpc-7vxp-69p6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/http4k/http4k/commit/0121b05537"
    },
    {
      "type": "WEB",
      "url": "https://github.com/http4k/http4k/commit/54c6385615"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/http4k/http4k"
    },
    {
      "type": "WEB",
      "url": "https://github.com/http4k/http4k/releases/tag/6.49.0.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "http4k: `reverseProxy()` defaulted to substring (`Contains`) matching on `Host`; tightened to `Exact`"
}