Cross-site scripting (XSS) vulnerability in errorfe.aspx in Outlook Web App (OWA) in Microsoft Exchange Server 2013 SP1 and Cumulative Update 7 allows remote attackers to inject arbitrary web script or HTML via the msgParam parameter in an authError action, aka "Exchange Error Message Cross Site Scripting Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2015/ms15-026