Proxy service crash DoS

How it was found

Sending certain URLs to the proxy appears to crash the service, leading to a 502 Bad Gateway from nginx, presumably until the service is restarted. The following sequence sent in a short period appears to cause the crash (it could just be the javascript:confirm() request, as the last request receives the 502, but I can't re-test to be sure):

http://staging.fct.li/?url=data:text/html,Hello http://staging.fct.li/?url=data://text/html,Hello http://staging.fct.li/?url=data://staging.fct.li/ http://staging.fct.li/?url=javascript:confirm() http://staging.fct.li/?url=javascript:confirm("staging.fct.li")