IBM researchers uncovered an attack that could allow a hacker to impersonate someone by abusing the social login mechanism.

Social login is a form of single sign-on that uses existing login information from a social network, such as Facebook or Google+, to sign into a third-party website. According to IBM's X-Force Application Security Research Team, the attack -- which they have dubbed "SpoofedMe" -- works this way: A cyber criminal registers a spoofed account within a vulnerable identity provider using the victim's email address. Then, without having to actually confirm ownership of the email address, the attacker will log into the relying website with the fake account, via social login. The relying website will check the user details asserted by the identity provider and log the attacker into the victim's account, based on the victim's email address value, Or Peles, a security researcher with X-Force, explains in a blog post.

IBM found the issue impacted identity providers Amazon, LinkedIn, and MYDIGIPASS, all of which have taken steps to fix the problem. In one case, IBM discovered the issue could have allowed an attacker to intrude into a Slashdot.org user account using the "Sign In With LinkedIn" service. Once logged in, an attacker would have had total access to the victim's account. LinkedIn responded to the issue quickly and fixed the vulnerability after the attack was disclosed, Peles wrote.  

The attack relies on a combination of two things: a vulnerable identity provider and one of two design problems in the relying website.

"A common relying website design problem is the use of an email address as a sufficiently unique identifier for its local user accounts without verifying the specific identity provider(s) previously used with the account," Peles blogs. "This means that claiming (using an identity provider) to own an email address is enough to log a user in to the local account that uses the same email address. This design problem may arise in cases where support for social login providers was added to an existing system without redesigning the user database in the migration process."

The other design issue for relying sites is account linking, which lets users log into their local account more than one way.  

"When, for the first time, a user logs in with a different identity provider (than previously used with his or her existing local account) and uses an email address that is identical to that of his or her existing account, a website could assume he or she is the owner of the account and automatically link the new identity with the existing local account without asking for any additional credentials," Peles explains.

When it comes to identity providers, IBM found that some agree to supply the account email addresses as part of the social login authentication process even when the user's ownership of the email address has not been positively verified.

In order for the attack to work, the third-party website must support social login with a vulnerable identity provider and request the email address field as part of the social login authentication process. In addition, the third-party site must support at least one other login option either using another identity provider or the ability to use a local website account's credentials. There also must be a victim account whose email address is known and that doesn’t own an identity account with this email address at the vulnerable identity provider.

Diana Kelley, executive security advisor for IBM Systems, tells Dark Reading that there could be thousands of websites vulnerable to this attack. In addition to identity providers Sign-In with LinkedIn, Login with Amazon, and MYDIGIPASS.COM Secure Login, the following relying websites were found to be affected by the issue: Spiceworks.com, Crowdfunder.com, Slashdot.org, Nasdaq.com, Scoop.it, and Idealist.org.

"This is fairly simple to exploit if both the relying website (e.g. NASDAQ/Slashdot) and the identity provider (e.g. LinkedIn before the fix) are vulnerable," she explains in an email. "To exploit it requires registering for an account with an email address that is in use at the relying site but not in use at the ID provider and then using the social login function to login at the relying site."

According to IBM, the implications are serious, as it could be used for a number of malicious activities, including impersonating company executives in a stock forum or other public website with the goal of affecting stock prices. It could also be used to leverage someone's reputation to spread malicious links or malware, or defame them by posting controversial material.

"While fixing the identity provider vulnerability would be enough for this attack to be blocked … it is important for websites that are vulnerable to fix the website design problem because it may expose their users to similar attacks," Peles adds.