Ambiguous IPv6 in Origin headers may bypass webserver access restrictions — Mozilla

Security researcher Simone Fabiano reported that if a cross-site XHR or WebSocket is opened on a web server on a non-standard port for web traffic while using an IPv6 address, the browser will send an ambiguous origin headers if the IPv6 address contains at least 2 consecutive 16-bit fields of zeroes. If there is an origin access control list that uses IPv6 literals, this issue could be used to bypass these access controls on the server.