Pixelfed: Authenticated SSRF via Remote URL Search

Pixelfed's SearchController (behind the auth middleware) accepts a URL via its remote-search parameters and fetches it server-side through ActivityPubFetchService, whose validateUrl() only blocks the literal hosts 127.0.0.1, localhost, and ::1 and requires https, without checking the resolved IP against private, internal, or link-local ranges (e.g. 169.254.169.254). Optional DNS validation is disabled by default and, when enabled, only confirms a DNS record exists without filtering by IP range. The fetch response body is returned to the requester only when the Content-Type matches an ActivityPub content type, making this a semi-blind but authenticated SSRF primitive reachable by any logged-in user.