OAuth 2.0 and OpenID have serious Covert Redirect vulnerability. It could lead to Open Redirect Attacks to both clients and providers of OAuth 2.0 or OpenID. For OAuth 2.0, these attacks might jeopardize “the token” of the site users, which could be used to access user information. In the case of Facebook, the information could include the basic ones, such as email address, age, locale, work history, etc. If “the token” has greater privilege (the user needs to consent in the first place though), the attacker could obtain more sensitive information, such as mailbox, friends list and online presence, and even operate the account on the user's behalf. For OpenID, the attackers may get user's information directly. Compounded by the large number of companies involved, this vulnerability could lead to huge consequences if left unresolved. http://tetraph.com/covert_redirect/oauth2_openid_covert_redirect.html