What Does ColdFusion's verifyClient() Do?

I recently saw a ColdFusion question about verifyClient and remote CFC functions.  I already have strong opinions about why you don't want to use remote CFC functions, but I was unfamiliar with verifyClient.  That led me to take a look at how it works and I thought it was interesting enough to write about.  

Thinking Defensively About Three Recent Lucee Vulnerabilities

Last week, Harsh Jaiswal and Rahul Maini from ProjectDiscovery released some impressive security research on multiple vulnerabilities in Lucee (and Mura CMS and Masa CMS).  Their blog post is a must-read, and I'm not going to rehash their steps from research to discovery to exploitation.  Instead, I'm going to look at these vulnerabilities through a defensive lens.