Pterodactyl's improper JWT scoping allows subuser to upload files when not explicitly granted `file.create` permissions

Summary

A privilege escalation vulnerability exists in the Wings /upload/file endpoint due to insufficient validation of panel-signed JWTs. Wings accepts any valid panel-signed JWT containing server_uuid, user_uuid, and unique_id, regardless of the token’s intended purpose. Because the Panel issues JWTs with these same claims for other lower-privilege operations (such as WebSocket authentication and file download links), an authenticated subuser can reuse one of those tokens to upload arbitrary files without possessing the required file.create permission.

Impact

Any subuser with permission to connect to a server's console, download files, or download backups could reuse those tokens to upload arbitrary files to the same server. A user that does not have access to a server as a subuser is not able to arbitrarily upload files.

Details

The panel generated JWT tokens for various purposes:

• https://github.com/pterodactyl/panel/blob/0f82c105201b192d229f6abd5827e2ee7e672a05/app/Services/Backups/DownloadLinkService.php#L33-L36
• https://github.com/pterodactyl/panel/blob/0f82c105201b192d229f6abd5827e2ee7e672a05/app/Http/Controllers/Api/Client/Servers/FileUploadController.php#L45
• https://github.com/pterodactyl/panel/blob/0f82c105201b192d229f6abd5827e2ee7e672a05/app/Http/Controllers/Api/Client/Servers/WebsocketController.php#L58-L61
• https://github.com/pterodactyl/panel/blob/0f82c105201b192d229f6abd5827e2ee7e672a05/app/Http/Controllers/Api/Client/Servers/FileController.php#L82-L85 Though as the actual purpose is not conveyed part of the JWT tokens, this introduces this vulnerability of being able to do non-intended actions due to the expected fields (i.e. server_uuid) on most endpoints being the same when parsing it on wings' side.

PoC

Create a new subuser that has the minimal amount of permissions on a server (websocket.connect). As that subuser, retrieve a websocket JWT token from the GET /api/client/servers/[...]/websocket endpoint (in my case, I manually just make a request under that user's browser session; you can probably just resend the /websocket request in browser console to get a fresh unused token). Using that websocket token, we can abuse this by directly using it in the /upload/file endpoint of the wings node instead of using it for websocket authentication:

import requests

wings_url = 'http://[...]:8080'
websocket_token = '[...]'

res = requests.post(f'{wings_url}/upload/file', params = {
    'token': websocket_token,
}, files = {
    'files': ('file-upload.txt', b'Hello, World!'),
})
print(res.status_code, res.content)

Observe, that even though our subuser never has permissions outside viewing the console, they are able to write arbitrary files in the server. This pattern happens in a lot of other action, but this is probably the most interesting one.