I had the same issue, I found it by googling the KB id. http://download.microsoft.com/download/B/0/A/B0AEBD7D-6979-4265-B1AC-A0B73618FB22/AspNet5.ENU.RC1_Update1.exe
or this:
http://download.microsoft.com/download/1/8/0/18048EDD-9F45-479A-B208-6F7C91CF2ECC/AspNet5.ENU.RC1_Update1_KB3137909.exe