: Ensure you have a valid Cisco account. If you don't have one, you'll need to create it. Cisco often requires registration to access software downloads.
Before installing CUCM 12.5, ensure that your system meets the minimum requirements: Cisco Cucm 12.5 Download
Click the version drop-down. You will see several sub-options: : Ensure you have a valid Cisco account
certutil -hashfile UCSInstall_UCOS_12.5.1.11900-8.sgn.iso SHA512 Cisco Cucm 12.5 Download