Vulnerability is reported in Google by "Ucha Gobejishvili ( longrifle0x )". This problem may assist an attacker to conduct phishing attacks, trojan distribution, spammers.
Url: https://accounts.google.com/o/oauth2/auth?redirect_uri=http://www.something.com

Same vulnerability in Facebook, Discovered by ZeRtOx from Devitel group:
http://www.facebook.com/l.php?h=5AQH8ROsPAQEOTSTw7sgoW1LhviRUBr6iFCcj4C8YmUcC8A&u=www.something.com