Koel v9.6.0 protects its regular podcast subscription API URLs with SafeUrl validation to prevent SSRF to private/internal addresses. However, the Subsonic-compatible createPodcastChannel.view route does not apply SafeUrl validation and only checks that the URL is a string and a valid URL format. This discrepancy allows an authenticated user to supply a private/internal URL that Koel fetches server-side immediately during podcast channel creation. The SSRF occurs as part of the podcast parser's addPodcast() function, which calls Poddle::fromUrl() on the attacker-controlled URL. This bypasses Koel's intended SSRF protections on podcast URLs. The vulnerability was validated using the official phanan/koel:9.6.0 Docker image. The main API rejects private URLs with a 422 error, but the Subsonic route accepts and processes them, causing Koel to make HTTP requests to internal services reachable from the server. The vulnerability is distinct from a prior SSRF fixed in versions <= 9.3.4. The suggested remediation is to apply SafeUrl validation to the Subsonic podcast URL input and add defense-in-depth checks in the podcast parser entry point.

An authenticated attacker can cause Koel to make server-side HTTP requests to internal network destinations that are normally blocked by the main API. This includes loopback addresses, Docker bridge IPs, and RFC1918 private IP ranges reachable from the Koel server. The impact is SSRF-based internal service discovery and request execution. No confirmed data exfiltration or remote code execution has been demonstrated through this vulnerability. The SSRF can be used to probe internal services and potentially interact with them via HTTP requests initiated by Koel.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vendor recommends applying the SafeUrl validation rule to the Subsonic createPodcastChannel.view route to block private/internal URLs, consistent with the main podcast API. Additionally, adding validation in the podcast parser entry point to reject unsafe URLs is advised as defense in depth. Until a patch is available, restrict access to trusted authenticated users and monitor for unusual internal HTTP requests originating from Koel.