{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.17.16"
      },
      "package": {
        "ecosystem": "Go",
        "name": "https://github.com/dadrus/heimdall"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.17.17"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-116",
      "CWE-20",
      "CWE-290"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-18T14:24:37Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\nWhen the `trusted_proxies` option is configured, heimdall extracts client IP addresses from the `Forwarded` (`for=` parameter) and `X-Forwarded-For` headers and exposes them as `Request.ClientIPAddresses` to the rule pipeline. However, extracted values are not validated to be syntactically valid IP addresses. Arbitrary strings, malformed IP literals, and RFC 7239 `unknown` values and obfuscated identifiers are accepted without further checks.\nIn addition, the `Forwarded` header parser splits on `,` and `;` without accounting for RFC 7239 quoted strings, which can cause a single quoted value to be parsed as multiple entries, with fragments \u2014 including trailing quote characters \u2014 treated as independent addresses.\n\n### Impact\n\n`Request.ClientIPAddresses` is available to all pipeline mechanisms. Its contents can therefore influence rule evaluation in deployments where rules reference this property \u2014 for example, in a `CEL` authorizer that checks whether a request originates from a trusted IP range using the `networks()` function, or in a `Remote` authorizer that forwards the client IP as part of its payload to an external authorization system. Whether and how `Request.ClientIPAddresses` is used is entirely determined by the rule configuration.\n\nAdditionally, in proxy mode, `Request.ClientIPAddresses` is used directly to construct the `X-Forwarded-For` and `Forwarded` headers forwarded to upstream services. Injected or malformed values are therefore propagated to upstream services unchanged.\n\n### Attack Scenarios\n\nAll scenarios require that `trusted_proxies` is configured. If this option is not set, heimdall ignores forwarding headers entirely, and this vulnerability is not exploitable. Scenarios A and C  (see below) additionally require that rules reference `Request.ClientIPAddresses` in their pipeline.\n\n#### Scenario A \u2013 Manipulation of rule evaluation\n\nAn attacker who can influence forwarding headers \u2014 either by connecting directly to heimdall or through a proxy that does not sanitize these headers \u2014 can inject arbitrary values into `Request.ClientIPAddresses`. In deployments where a rule references this property (e.g. to restrict access to specific IP ranges), this may allow an attacker to bypass the intended access control logic.\n\n#### Scenario B \u2013 IP spoofing against upstream services (proxy mode)\n\nIn proxy mode, injected or malformed values in `Request.ClientIPAddresses` are written unchanged into the `X-Forwarded-For` header sent to upstream services. Upstream services that trust this header may therefore receive and act on attacker-controlled IP values.\n\n#### Scenario C \u2013 Malformed entries via quoted-string misparse\n\nA `Forwarded` header containing a quoted value with embedded delimiters (`,` or `;`) is misparsed, producing unintended additional entries in `Request.ClientIPAddresses`, including malformed fragments with trailing quote characters.\n\n### Workarounds\n\n* Ensure at the network level that only trusted proxies can communicate directly with heimdall.\n* Ensure that the proxy forwarding the requests to heimdall sanitizes or overrides (not merely appends to) `Forwarded` or `X-Forwarded-For` headers before forwarding them.\n* Avoid relying on `Request.ClientIPAddresses` for security-sensitive decisions until patched",
  "id": "GHSA-38x9-25wx-7fg2",
  "modified": "2026-06-18T14:24:37Z",
  "published": "2026-06-18T14:24:37Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/dadrus/heimdall/security/advisories/GHSA-38x9-25wx-7fg2"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/dadrus/heimdall"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Heimdall: IP Spoofing via Unvalidated Forwarding Headers"
}