GHSA-8q6q-m837-fv64: Koel has SSRF through Authenticated Subsonic podcast feed URLs

Koel’s Subsonic createPodcastChannel.view endpoint accepts a user supplied podcast feed URL and fetches it server-side before applying the safe URL checks that are used for podcast episode enclosure URLs. An authenticated Subsonic API user can provide a loopback or internal URL as the feed URL and cause the Koel backend to issue a request to that address.

A related redirect gap exists in the podcast stream helper: PodcastService::getStreamableUrl() validates only the original URL, then lets Guzzle follow redirects and accepts the final redirected URL without re-validating it.