Grafana: Path traversal in the Tempo and Loki data source plugins

The Tempo and Loki datasource plugins construct backend HTTP requests by interpolating user-supplied input into URL paths without sanitization, enabling path traversal. A Viewer-role user can: (1) capture admin-configured datasource credentials (secureJsonData custom headers) by traversing to an attacker-controlled endpoint, (2) invoke state-changing admin endpoints on Tempo (e.g. /flush, /shutdown), and (3) exfiltrate internal service data via Loki's CallResource which returns full HTTP response bodies.