Is TLS 1.1/1.2 enabled by default in .NET 4.5 and .NET 4.5.1?
No. The default protocols enabled for the various framework versions are:
- .NET Framework 4.5 and 4.5.1: SSLv3 and TLSv1
- .NET Framework 4.5.2: SSLv3, TLSv1, and TLSv1.1
- .NET Framework 4.6 and higher: TLSv1, TLSv1.1, and TLS1.2
Sources: [1] [2] [3]
While Microsoft recommends against explicitly specifying protocol versions in favour of using the operating system’s defaults:
To ensure .NET Framework applications remain secure, the TLS version should not be hardcoded. .NET Framework applications should use the TLS version the operating system (OS) supports.
… it’s still possible to select which protocols your application supports by using the ServicePointManager class, specifically by setting the SecurityProtocol property to the relevant SecurityProtocolTypes.
In your case you would want to use the following:
System.Net.ServicePointManager.SecurityProtocol =
SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
Note that TLSv1 and TLSv1.1 are effectively deprecated as of 2020; you should avoid building new applications that rely on these protocols, and make every effort to upgrade applications that currently use them.