Pi-hole is a DNS sinkhole that protects devices from unwanted content without installing any client-side software. A vulnerability in versions prior to 5.18.3 allows an authenticated user to make internal requests to the server via the gravity_DownloadBlocklistFromUrl() function. Depending on some circumstances, the vulnerability could lead to remote command execution. Version 5.18.3 contains a patch for this issue.
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.