If OWA and ECP are not accessible after a failed Exchange Cumulative Update try the following to fix:

Copy over Cumulative Update files over to a different server

Example: \\RG-DC\c$\temp\CumulativeUpdate23\

Share out the CumulativeUpdate23 folder 

On the Mail server in a command prompt run the following command:

Example: \\RG-DC\c$\temp\CumulativeUpdate23\setup.exe /Mode:Upgrade /IAcceptExchangeServerLicenseTerms