{"id":"GHSA-38x9-25wx-7fg2","summary":"Heimdall: IP Spoofing via Unvalidated Forwarding Headers","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 — 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","aliases":["CVE-2026-57210","GO-2026-5075"],"modified":"2026-08-11T20:51:05.251114822Z","published":"2026-06-18T14:24:37Z","database_specific":{"cwe_ids":["CWE-116","CWE-20","CWE-290"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-06-18T14:24:37Z","nvd_published_at":null},"references":[{"type":"WEB","url":"https://github.com/dadrus/heimdall/security/advisories/GHSA-38x9-25wx-7fg2"},{"type":"PACKAGE","url":"https://github.com/dadrus/heimdall"}],"affected":[{"package":{"name":"https://github.com/dadrus/heimdall","ecosystem":"Go","purl":"pkg:golang/https:/github.com/dadrus/heimdall"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.17.17"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-38x9-25wx-7fg2/GHSA-38x9-25wx-7fg2.json","last_known_affected_version_range":"\u003c= 0.17.16"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","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"}]}