Prohibiting a user from reviewing and closing their own ticket?

[1chrisanderson]

I'm trying to find a way to disallow the assignee of an issue from sending their own ticket all the way through our change management process without external review and approval. 

Here's our current workflow : 

The desired state would be a condition on the transition between "Ready for CM Review" and "Under Review" that is only possible when the action is taken by someone other than the assignee.   I looked around in the pre-built conditions and didn't see anything that would be helpful, is there some way to accomplish this without a 3rd party plugin?  

[Joe Pitt]

You can't restrict the assignee, however you can put a condition that only a user with the transition permission can execute the transition 

copy/paste link  https://confluence.atlassian.com/jirakb/how-to-prevent-specific-users-from-executing-workflow-transitions-244351800.html 

That is the best I can figure if you don't want a plugin