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Researchers have uncovered a phishing attack using a new technique: Attackers are making use of authentication APIs to validate victims’ Office 365 credentials – in real time – as they enter them into the landing page.

Authentication APIs are used by apps and services running on the users’ behalf to access their data, Prashanth Arun, head of Data Science at Armorblox, told Threatpost. Office 365 requires app registrations to use APIs – but registrations require only an email address, making them seamless for attackers to leverage. Some additional configuration for the app also requires users to specify a website to “receive” authentication info, Arun added.

In a phishing attack recently spotted by researchers, the attacker used the authentication APIs to cross check the credentials of a senior executive at a large enterprise firm with the organization’s Azure Active directory. Active Directory (AD) is Microsoft’s proprietary directory service, which allows administrators to manage permissions and access to network resources. The authentication APIs use Azure AD to provide authentication services.

In the phishing attack, access to this immediate feedback “allows the attacker to respond intelligently during the attack,” researchers with Armorblox said on Thursday. “The attacker is also immediately aware of a live compromised credential and allows him to potentially ingratiate himself into the compromised account before any remediation.”
 
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