Moto X4 started getting September security patch from Motorola. The update is arriving as build NPW26.4 that brings critical fix for Blueborne vulnerability along security patch for the month of September. The OS version stays on Android 7.1.1 Nougat because it’s not an incremental update, it’s a minor security fix update that resolves 30 issues dated 2017-09-01, and 51 issues in the one dated 2017-09-05.
Moto X4 gets September security patch via build NPW26.4
You can download the update via OTA but remember to charge your device at minimum 60% to avoid shutdown during the process and also set up a working internet connection to download the update. It is always recommended to keep your device updated regarding firmware updates. The OTA has landed already just go to Settings > About device > System updates.
It is always recommend to keep your device updated regarding necessary security updates. Android security updates mostly deal with the deadly vulnerabilities according Android’s security bulletin “One of them is the issue with critical security vulnerability in media framework that could enable a remote attacker using a specially crafted file to execute arbitrary code within the context of a privileged process. The severity assessment is based on the effect that exploiting the vulnerability would possibly have on an affected device, assuming the platform and service mitigation is turned off for development purposes or if successfully bypassed”.