Answer

Yes, ASP.NET 4.5 is supported by Plesk 11 and 12.

Below are the lists of ASP.NET versions supported by PP versions:

Plesk 9.5:

  • ASP.NET 1.1.4322
  • ASP.NET 2.0.50727 (.Net Framework 2.0/3.0/3.5)
  • ASP.NET 4.0

Plesk 10.4:

  • ASP.NET 1.1
  • ASP.NET 2.0
  • ASP.NET 4.0

Plesk 11:

  • ASP.NET 1.1 - 4.5

Plesk 11.5:

  • ASP.NET 1.1 - 4.5

Plesk 12:

  • ASP.NET 1.1 - 4.5

Note #1: As .NET 4.5 Framework is iterative update to .NET 4.0, Plesk and IIS will continue displaying available version of ASP.NET as 4.0.

Note #2: See KB article #115727 for instructions on how to set up .NET 1.1 Framework on Windows 2008 with IIS7.

This information was taken from the applicable release notes:

Plesk 9.5 Release Notes

Plesk 10.4 Release Notes

Plesk 11.0 Release Notes

Plesk 11.5 Release Notes

Plesk 12 Release Notes

Internal content