The attack was revealed by Cybereason security company when Microsoft requested its services.
Microsoft's Outlook Web Application (OWA) is a web portal webmail server, που υπάρχει σαν χαρακτηριστικό του Microsoft Exchange Server. Ο Exchange Server επιτρέπει σε εταιρείες αλλά και ιδιώτες που τρέχουν το functional system to develop their own email services.
As Cybereason security company explains, attackers replaced OWAAUTH.dll with one that contained a backdoor. So they were able to collect information from the local Directory Server authentication procedures (a server that manages the common authentication procedures).
So while all authentication processes were working correctly on the Outlook Web Application server using SSL/TLS encryption, the DLL file allowed hackers to obtain all login information in plain text, since the DLL has access before the encryption stage.
All recorded data were stored in a log.txt file on the server. Its researchers Cybereason they discovered more than 11.000 usernames and passwords access in this file. The company that ran the OWA server has about 19.000 employees.
Hackers are reportedly taking measures to prevent the attack from being revealed, but if the backdoor is found to be difficult to remove. They created a filter on IIS (Microsoft Web Server) through which they uploaded the malicious OWAAUTH.dll file whenever the server was restarted.