Security Experts:

Microsoft Pays $24,000 for Authentication Flaw in

Microsoft has awarded a $24,000 bug bounty to a security researcher who uncovered a serious authentication vulnerability in the service. is the website used by Microsoft account owners to authenticate to, OneDrive, People and various other services. Wesley Wineberg, senior security research engineer at Synack, discovered a serious flaw in the service’s authentication mechanism.

The expert found that an attacker could have hacked accounts simply by tricking authenticated users into visiting a malicious website. The vulnerability could have also been exploited by a worm designed to harvest information from the victim’s address book and send out links pointing to an attack site to all the contacts, Wineberg said.

A demo video published by the researcher shows the exploit in action, which he claims could have been designed to run in the background or as part of a malicious ad banner to avoid raising any suspicion.

The security hole was related to the way Microsoft used OAuth, the authentication protocol that enables users to authorize third-party apps to access to their account without sharing the password.

Normally, the OAuth authorization process requires the user to specifically grant access to each application, but the researcher discovered a cross-site request forgery (CSRF) vulnerability in one of the APIs used to process the login that allowed him to eliminate the need for user interaction.

“Looking back at it all however, this really is just a classic CSRF vulnerability. The only thing that’s surprising about it is that it’s in a critical authentication system which ultimately can be used to take over any user’s account,” Wineberg noted in a blog post.

The vulnerability was reported to Microsoft on August 25 and it was patched on September 15, just over two weeks after the company confirmed its existence.

Wineberg says it’s difficult for him to determine for how long the vulnerability may have existed or if anyone has attempted to exploit it.

Microsoft announced in August that it had doubled bug bounty payouts for anti-exploitation techniques reported through its Bounty for Defense program. The company also announced at the time that it was prepared to pay double bounty rewards, up to $30,000, for vulnerabilities found between August 5 and October 5 in three Microsoft Accounts domains, namely, and

Since Wineberg reported his findings on August 25, he was eligible for the bonus and Microsoft awarded him $24,000.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.