Cross-site scripting (XSS) vulnerability in Microsoft ASP.NET SignalR 1.1.x before 1.1.4 and 2.0.x before 2.0.1, and Visual Studio Team Foundation Server 2013, allows remote attackers to inject arbitrary web script or HTML via crafted Forever Frame transport protocol data, aka "SignalR XSS Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2013/ms13-103