Blombooru is a self-hosted personal booru for organizing and tagging private image collections. Prior to 1.40.0, the administrator-only GET /proxy-image endpoint, exposed as /api/booru-import/proxy-image, accepts a url query parameter and fetches it server-side without meaningful destination validation. proxy_image() in backend/app/routes/booru_import.py only checks whether the value starts with http, then uses get_client_for_url or requests.get and streams the response. Private, loopback and link-local addresses are not blocked, and automatically followed redirects can move a request from a trusted domain to an internal address. An authenticated administrator can enumerate internal services and access cloud instance metadata, potentially disclosing IAM credentials and crossing the…