Server-Side Request Forgery (SSRF) and URL Redirection to Untrusted Site ('Open Redirect') in alltube

alltube is an html front end for youtube-dl. On releases prior to 3.0.3, an attacker could craft a special HTML page to trigger either an open redirect attack or a Server-Side Request Forgery attack (depending on how AllTube is configured). The impact is mitigated by the fact the SSRF attack is only possible when the `stream` option is enabled in the configuration. (This option is disabled by default.) 3.0.3 contains a fix for this vulnerability.