Apple over the weekend reissued a security update for OS X El Capitan systems after the initial update blocked Apple’s own Ethernet drivers.
The initial security update, which was installed on systems automatically in the background, was meant as a security measure designed to block kernel extensions that were harmful to the operating system. Apple issued the update to blacklist problematic kernel extensions, but mistakenly included the kernel extension information for its Ethernet drivers in it.
As soon as the update was installed on target OS X El Capitan machines, a process that did not require any user interaction, the Ethernet drivers were blocked and the affected Macs could no longer connect to the Internet via an Ethernet connection.
However, Apple soon realized the issue and decided to reissue the security update to resolve the blacklisting problem. The company also published a knowledgebase article to provide users with the required information about the issue.
Following the buggy update, users could see in the System Information status that version 3.28.1 of Incompatible Kernel Extension Configuration Data was installed. This also meant that the Ethernet connection was affected if the Mac was rebooted after the update, and that the machine needed to be updated to version 3.28.2 to fix the problem.
According to Apple, the Wi-Fi connection, which uses separate drivers, was not affected, and Macs that connected to the Internet over Wi-Fi were automatically updated to version 3.28.2. Should the Wi-Fi connection not work, however, users needed to manually install the reissued update to resolve the Ethernet connectivity bug.
Affected users need to restart from OS X Recovery by holding down Command-R while the Mac starts up, select Disk Utility from the list of OS X Utilities, then select their drive from the list of internal drives in the sidebar. If the drive is protected by FileVault, users need to Choose File > Unlock from the Disk Utility menu, then enter the FileVault password.
Next, users should Choose File > Mount in Disk Utility to mount the drive if it's not already mounted, quit Disk Utility, then Choose Utilities > Terminal to open the Terminal app, and type or paste the following command as one line in Terminal, then press Return: rm -rf "/Volumes/Macintosh HD/System/Library/Extensions/AppleKextExcludeList.kext" (where the Macintosh HD should be replaced with the name of user’s hard drive, if different).
After that, users should quit Terminal and restart the Mac, having the Ethernet connection working when the machine comes back online. Next, users should open Terminal and enter the following command: sudo softwareupdate –background, which forces a checking with the Apple software update service and automatically installs the latest update, after which they should quit Terminal and restart the Mac once more.