Microsoft .NET Framework 2.0 SP2, 3.0 SP2, 3.5, 3.5.1, 4.5.2, 4.6, and 4.6.1 mishandles signature validation for unspecified elements of XML documents, which allows remote attackers to spoof signatures via a modified document, aka ".NET XML Validation Security Feature Bypass."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-035