Koel's Subsonic `createPodcastChannel.view` endpoint accepts user-supplied podcast feed URLs and fetches them server-side before applying safe URL checks, which are only applied later to episode enclosure URLs. This allows an authenticated Subsonic API user to provide loopback or internal URLs, triggering SSRF requests from the Koel backend to internal services. The podcast stream helper method `PodcastService::getStreamableUrl()` validates only the original URL and then follows redirects without re-validating the final redirected URL, accepting potentially unsafe internal URLs. The root cause is that the feed URL is not validated against the safe URL policy before fetching, and redirect targets are not re-validated. This enables blind SSRF against internal HTTP endpoints accessible by the Koel host. The vulnerability affects Koel versions prior to 9.7.0.

An attacker with any valid Koel account and Subsonic API key can cause the Koel server to make HTTP requests to internal or loopback network addresses. This can be used to perform blind SSRF attacks against internal services reachable from the Koel host. If internal services respond with valid RSS/XML or permissive CORS headers, parts of the response or final URLs may be reflected back to the attacker through normal podcast or streaming functionality. This could lead to information disclosure about internal network services. There is no indication of direct remote code execution or denial of service from this vulnerability.

No official patch or fix is currently available. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Mitigation involves validating the podcast feed URL against the safe URL policy before any server-side fetching occurs. Additionally, all redirect targets must be re-validated before following redirects or automatic redirects should be disabled and handled manually with validation. Regression tests should be added to detect loopback, private IP, and redirect-based SSRF attempts. Until a fix is released, restrict access to trusted users and monitor for suspicious Subsonic API usage.