"System Extension Blocked" after upgrade to macOS 10.14 Beta (18A293u)
There is a workaround for this. I don't recommend it from a security perspective, but it does get you back to the behavior of macOS 10.12 until Cisco  gets around signing the kernel extension for your VPN client.

Basically, you can turn off the security feature requiring user approval of Kernel Extensions.

First, boot into Recovery Mode by rebooting and pressing and holding command-R as soon as you see the Apple logo.

Eventually you will see a screen that gives you a couple of options, including reinstalling or running Disk Utility.



If you look at the menubar at the top, you will see a "Utilities" drop-down menu. Click on that and select Terminal. A window will open up that allows you to type text-based terminal commands.

You will see a "$" prompt in the terminal window. Type the following:


  spctl kext-consent disable


then press Return. You should see:


  Kernel Extension User Consent: DISABLED
  
  Please restart for changes to take effect.


Then reboot your Mac, and you should be good. You will no longer see the notification panes telling you a Kernel Extension was blocked; they will all be automatically allowed, just as they were in macOS 10.12.

Don't forget to re-enable kernel extension verfication after the full release of macOS 10.14.


  spctl kext-consent enable


For more information, see the following User Approved Kernel Extension: