Recent OS X Update Breaks Ethernet In Macs
A recent OS X security update introduces a bug that stops the Ethernet port in most Macs to stop working. As Reddit user "zorinlynx" pointed out, a recent OS X security update called "031–51913 Incompatible Kernel Extension Configuration Data 3.28.1" blacklists the BCM5701 driver. Most Mac PC's depends on the BCM5701 driver for proper working of Ethernet ports. With the update blacklisting the driver, users are reporting that their Ethernet port is not working.
Apple has since pulled the update from their update servers, but it looks like quite a few users are affected. Apple has not provided any timeline for a fix to the affected users. However, we guess we might see an update in the coming week that may have a fix for this issue.
If you cannot wait until an official fix and are willing to mess with your Mac, then some geek users have posted a solution on Reddit that requires affected users to restore the file "/System/Library/Extensions/AppleKextExcludeList.kext" from a Time Machine or from another Mac running the same software version.
For those who do not want to tinker your Macs, you have to wait until Apple release a fix.
Apple has posted a support document for this issue detailing steps to resolve this issue.
In simple terms, connect your Mac to Wi-Fi and run the update program (type "sudo softwareupdate –background" from a terminal). It will update "Incompatible Kernel Extension Configuration Data" to 3.28.2, which will fix the issue.
If you cannot connect to Wi-Fi, then you have to restart your Mac in OS X Recovery and delete "/System/Library/Extensions/AppleKextExcludeList.kext" file. You can visit this Apple Support page on how to do it.