Microsoft ended the support for the first version of .NET Core, as per the support policy.
As per this .NET Core 1.0 and 1.1 reached end of support on June 27, 2019. This version will no longer receive any updates going forward. The final update released for .NET Core 1.0 and 1.1 are 1.0.16 and 1.1.13, respectively.
So, all developers are advised to upgrade your existing applications to .NET Core 2.1 or above.