Bazarr Blind Server-Side Request Forgery (SSRF) in the /test/<protocol>/ endpoint

Bazarr manages and downloads subtitles. In version 1.2.4, the proxy method in bazarr/bazarr/app/ui.py does not validate the user-controlled protocol and url variables and passes them to requests.get() without any sanitization, which leads to a blind server-side request forgery (SSRF). This issue allows for crafting GET requests to internal and external resources on behalf of the server. 1.3.1 contains a partial fix, which limits the vulnerability to HTTP/HTTPS protocols.