Sierra: Security Update 2017-001 Sierra broke my WiFi Today, I installed Security Update 2017-001 for Sierra 10.12.6 and my WiFi is unable to get a DHCP IP address off anything any more. I trashed the usual suspects in /Library/Preferences/SystemConfiguration:


com.apple.airport.preferences.plist
com.apple.network.eapolclient.configuration
com.apple.wifi.message-tracer.plist
NetworkInterfaces.plist 


I rebooted to find nothing had changed. I tried setting up a new network location and connecting to a local WiFi access point but DHCP can't get an IP. I also reset SMC and NVRAM.
I like to remove the network interfaces entirely if someone manually delete plist files or changes things in the library directly and then restart to give the system a chance to recreate the files if it can. Especially on Sierra and later since the preference files aren’t canonical in most cases and the settings persist in a database and get flushed back to disk periodically when the defaults system commits a change. 


Remove WiFi interface from all locations (if you have network locations)
Restart
Add in the wirelesss network connection in system preferences


If that doesn’t work, next is two items. You may want to check the network with another device or two - the Mac update could be coincidence and not causal. If the network is working, then you’ll want to look at things other than the core os. 

Firewall (little snitch), anti virus (eset or Kaspersky), vpn software and anything that adds extensions or network modifications.