The `ScopingHttpClient` component in Symfony HttpClient merges default scope options, such as `auth bearer` or `auth basic`, into a request before resolving a relative URL against the `base uri`. This allows a network-path reference to be sent to a different origin while retaining the default scope credentials, potentially disclosing them to an attacker-controlled server. This occurs when the resolved URL falls outside the origin of the base URI, including cases with different ports or user-info on the same host. The issue is reachable if an attacker controls the beginning of a URL passed to a client configured with a `base uri` and credentials, specifically those created via `HttpClient::createForBaseUri()` or configured under `framework.http client.scoped clients`.