{"id":"CVE-2026-57210","aliases":["GHSA-38x9-25wx-7fg2"],"title":"Heimdall: IP Spoofing via Unvalidated Forwarding Headers","summary":"Heimdall: IP Spoofing via Unvalidated Forwarding Headers","severity":"high","vendor":"https:","product":"https://github.com/dadrus/heimdall","ecosystem":"go","affected":["https://github.com/dadrus/heimdall < 0.17.17"],"patched":["https://github.com/dadrus/heimdall 0.17.17"],"published":"2026-06-18","updated":"2026-07-20","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-38x9-25wx-7fg2","references":[{"url":"https://github.com/dadrus/heimdall/security/advisories/GHSA-38x9-25wx-7fg2"},{"url":"https://github.com/dadrus/heimdall"}],"tags":["osv","go"],"ingestedAt":"2026-07-21T19:04:57.969Z","slug":"CVE-2026-57210","body":"## Overview\n\n### 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 — including trailing quote characters — 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 — 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 – Manipulation of rule evaluation\n\nAn attacker who can influence forwarding headers — either by connecting directly to heimdall or through a proxy that does not sanitize these headers — 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 – 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 – 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\n\n## Affected packages\n\n- `https://github.com/dadrus/heimdall < 0.17.17`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `https://github.com/dadrus/heimdall 0.17.17`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}