Because CM12 and above no longer have root manager visible either in the app drawer or under the Settings options, many people thinks CM12 (and above) ROM are not pre-rooted hence, they will get busy looking for ways to root the ROM after installation. - This is like looking for something you already have in your hands, palms to be precise.
Unlike the previous versions of CM, CyanogenMOD ROM where you see root manager in the menu or under the Settings Options, starting from the CM 12 upward, no such thing is visible. However, that does not mean that the CM12 and above are not pre-rooted, you only need to use a different method to activate root privileges.
Although, following successful activation of the root privileges on the ROM (CM12 and above), you can't access the root manager yet. This is because CM now has a far more advanced Root Manager built-in. It automatically grants root access to every trusted apps that request for the root access and each access granted is only valid for that session. This means, regardless of the status, each app is granted root access only when it is requested and revoked when it's no longer in use.
How to Activate Root Privileges On CM12 ROMs and Above
Step #1: enable Developer Options. To do this, go to Settings » About » Build Number and tap it up to 7 times consecutively.
Step #2: Go to Settings » Developers Options » Root Access and then, select Enable Root for Apps and ADB.
Step#3: You can download and install any apps that require root privileges to function properly and lunch it. When it requests for root access, CM root manager prompts you for permission. Simply grant it root access.
It's as simple as that.