Streamlink: HTTPSession follows HTTP redirects into file:// URLs, reading local files

Summary

Streamlink is a CLI utility which pipes video streams from various services into a video player. Prior to 8.6.0, HTTPSession mounts a FileAdapter for the file scheme and inherits redirect handling from requests.Session without rejecting cross-protocol redirects. A remote server controlling an HTTP or HTTPS URL reached by Streamlink can return a redirect to a local file URL, causing HTTPSession to read the local file and return its contents to the response consumer. This bypasses the direct file URL checks added for HLS and DASH content because the manifest contains an ordinary network URL and the scheme transition occurs later during fetch handling. The flaw applies to every request made through HTTPSession, and a segment fetch can place the local file contents into stream output. This issue is fixed in version 8.6.0.