Koel v9.6.0 implements URL validation on its regular radio API endpoints using SafeUrl and HasAudioContentType checks, preventing SSRF. However, the Subsonic-compatible endpoints lack these validations, allowing authenticated users to supply arbitrary URLs, including private/internal addresses. These URLs are stored and later fetched by the server when streaming the radio station, with the response body proxied back to the client. This results in a full-read SSRF vulnerability, enabling attackers to read internal HTTP service responses accessible from the Koel server. The issue was confirmed on the official phanan/koel:9.6.0 Docker image. The vulnerability is tracked as CVE-2026-54493 and affects versions before 9.7.0.

An authenticated user can exploit this vulnerability to make the Koel server perform HTTP requests to internal or private network resources and read the full response content. This can lead to unauthorized disclosure of sensitive internal information accessible from the Koel server's network environment. The vulnerability does not allow code execution or denial of service but compromises confidentiality of internal services.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, restrict access to the Subsonic-compatible radio station endpoints to trusted users only. Monitor for updates from the Koel project regarding patches addressing this SSRF vulnerability. Avoid exposing Koel instances to untrusted networks or users.