Security Patch level old on Moto G5 My Moto G5's System Updates show that my device software is up to date. However the Security patch level shows up as "March 1 2017". 

Three months seems like a long time in the security exploits world. On the other hand, I see newer security patches on here: 

https://source.android.com/security/bulletin/2017-05-01

Is there a way to bring my phone up to date to the latest patches?
Although the OS of Moto phones bears a resemblance to Google's stock or AOSP, Moto themselves isn't as committed as Google themselves to bring security patches in time - in fact, they explicitly stated that they will NOT guarantee monthly security patches like Google does with its Nexus/Pixel line.

As of now there's nothing you can do if you want to keep your warranty and stay away from custom ROMs.