Microsoft .NET Framework 2.0 SP2, 3.0 SP2, 3.5, 3.5.1, 4.5.2, 4.6, and 4.6.1 allows man-in-the-middle attackers to obtain sensitive cleartext information via vectors involving injection of cleartext data into the client-server data stream, aka "TLS/SSL Information Disclosure Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-065