The web applications in Microsoft Exchange Server 2013 SP1 and Cumulative Update 8 allow remote attackers to bypass the Same Origin Policy and send HTTP traffic to intranet servers via a crafted request, related to a Server-Side Request Forgery (SSRF) issue, aka "Exchange Server-Side Request Forgery Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2015/ms15-064