Apple has come up with a fix for the issue with a recent security update that disabled the ethernet port on certain iMac and MacBook Pro models. The software update was: 031-51913 | Incompatible Kernel Extension Configuration Data 3.28.1.
Several users report that the update disabled their ethernet port, making the Macs unable to connect to a network via the ethernet port. Users were forced to use Wi-Fi to get online, if Wi-Fi was available.
User zorinlynx wrote:
After rebooting my ethernet didn’t work. Turns out that it added an exclusion for the stock AppleBCM5701Ethernet driver! This breaks ethernet and you have to use WiFi to get online.
While Apple quickly replaced the faulty update, users already affected were left in the lurch. Luckily, Apple posted a support document detailing how to determine if a system had been affected by the bad update, and how to fixed things with a new update, version 3.28.2.