Check used TLS version of .NET framework

[svndh]

Introduction
NuGet is a package manager, primarily used for packaging and distributing software written using the .NET framework and since April 2020 the NuGet support for TLS 1.0/1.1 was removed permanently for security reasons.

Especially for older operating systems like Windows Server 2012R2 or Windows Server 2016 TLS 1.2 is not set as a system default. The option of using TLS 1.2 was introduced in .NET 4.5, however, it is not enabled as a communication protocol by default in 4.5. Beginning with .NET 4.6, it is enabled as a communication protocol by default. Thus, in conjunction with the appropriate registry changes, .NET 4.6+ makes it possible to use TLS 1.2 without having to make code changes to explicitly enable it.

As a result older server which do not automatically use TLS 1.2 as system default have problems connecting to a NuGet Server with PowerShell Get 2.2.5 and higher.

Solution

Check whether .NET 4.x code select the strongest available protocol by default (i.e. when a protocol is not explicitly specified in code), check if the following registry keys are existent and set like in the following:

Registry Key	Value Name	DWORD Data
HKLM\SOFTWARE\Microsoft.NETFramework\v2.0.50727	SystemDefaultTlsVersions	0x00000001
HKLM\SOFTWARE\Wow6432Node\Microsoft.NETFramework\v2.0.50727	SystemDefaultTlsVersions	0x00000001
HKLM\SOFTWARE\Microsoft.NETFramework\v4.0.30319	SchUseStrongCrypto	0x00000001
HKLM\SOFTWARE\WOW6432Node\Microsoft.NETFramework\v4.0.30319	SchUseStrongCrypto	0x00000001

References
https://support.microsoft.com/en-us/topic/support-for-tls-system-default-versions-included-in-the-net-framework-3-5-on-windows-server-2012-db7ff0cb-fc9e-6530-db50-6a3dfc2834ad

https://github.com/TheLevelUp/pos-tls-patcher

https://devblogs.microsoft.com/nuget/deprecating-tls-1-0-and-1-1-on-nuget-org/