What is Exchange ActiveSync and how can it be used to access internal file shares?

Exchange ActiveSync (EAS) is a Microsoft Exchange protocol that synchronizes mail, calendar, contacts, and tasks between a mail server and mobile devices. Security researchers have demonstrated that by exploiting EAS's search functionality, an attacker with valid credentials can enumerate and read internal file shares—such as SYSVOL—without needing direct network access to those shares. Tools like PEAS automate this process, as detailed in the article on Penetration Techniques - Accessing Internal File Shares via Exchange ActiveSync.