A newly discovered zero-day vulnerability in Microsoft Exchange, tracked as CVE-2026-42897, poses a significant risk as it allows attackers to exploit cross-site scripting (XSS) to compromise Outlook Web Access (OWA) mailboxes. This vulnerability is reportedly under active attack, meaning that malicious actors are currently trying to exploit it in the wild. Organizations using Microsoft Exchange should be particularly vigilant, as the absence of an available patch leaves their systems exposed. Without immediate remediation, users could face unauthorized access to sensitive email communications. Companies are advised to implement security measures, such as input validation and monitoring for suspicious activity, until an official patch is released.