Heimdall has an authorization bypass via path normalization mismatch

### Summary Heimdall performs rule matching on the raw (non-normalized) request path, while downstream components may normalize dot-segments according to [RFC 3986, Section 6.2.2.3](https://www.rfc-editor.org/rfc/rfc3986#section-6.2.2.3). This discrepancy can result in heimdall authorizing a request for one path (e.g., `/user/../admin`, or URL-encoded variants such as `/user/%2e%2e/admin` or `/user/%2e%2e%2fadmin`. The latter would require the `allow_encoded_slashes` option to be set to `on` or `no_decode`.) while the downstream ultimately processes a different, normalized path (`/admin`). ### Details This vulnerability can be exploited by an adversary if rule matching is performed using free (named or unnamed) wildcards without further constraints, as shown in the example snippets below. ```yaml id: rule-1 match: routes: - path: /user/** execute: # configured to require authentication and authorization # ... ``` ```yaml id: rule-2 match: routes: - path: /public/** execute: # configured to allow anonymous access # ... ``` If an adversary sends a request to `/public/../user/whatever`, rule-2 will be matched and executed. The downstream service may, however, normalize the request path and interpret it as `/user/whatever`. ### Impact Bypass of access control policies enforced by heimdall may lead to the following consequences: * Access to or modification of data that should be restricted * Invocation of functionality that is expected to require authentication or authorization * In certain configurations, escalation of privileges depending on the exposed functionality ### Workarounds * Normalize HTTP paths or reject HTTP paths containing relative path expressions in the layers in front of Heimdall - this is good practice anyway. Some proxies do that by default, such as Traefik; others, such as Envoy, require additional configuration (for Envoy see [`normalize_path`](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/network/http_connection_manager/v3/http_connection_manager.proto#envoy-v3-api-field-extensions-filters-network-http-connection-manager-v3-httpconnectionmanager-normalize-path)). * Include the ID of the rule expected to be executed in the JWT issued by heimdall and check that value in the consuming project's service.

Source published

25 Apr 2026 23:30:46 UTC

Source modified

25 Jun 2026 18:56:30 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

Publisher rating · HIGH