A severe vulnerability in the way Microsoft Office 365 handles federated identities via SAML put an attacker in position to have access to any account and data, including email messages and files stored in the cloud-based service.
Microsoft pushed through a mitigation to the service on Jan. 5, seven hours after being notified by researchers Yiannis Kakavas and Klemen Bratec.
“The attack surface was quite big (Outlook Online, OneDrive, Skype for Business, OneNote – depending on what the company has paid for in terms of licensing ),” Kakavas and Bratec told ThreatPost via email. “And a malicious user exploiting this vulnerability could have gained access to very sensitive private and company information. (emails, internal documents etc. ).”