A security update rolled out to Mac users last week has broken connectivity on some iMac and MacBook Pro models. Users began reporting the issue online before Apple published a support document to confirm it and offer a solution.

“This update installed on my iMac today and my ethernet port stopped working,” says one Mac users on Reddit. “For some reason it blacklists the BCM5701 driver. Apple must have been testing something and this version of the blacklist escaped into the wild.”

With that driver blacklisted, Ethernet connectivity no longer works on some Macs, so users are unable to obtain a wired Internet connection. Apple has pulled the update now, but not before many users already installed it. Here’s how to find out if your Mac is affected:

1. While pressing the Option key, select System Information from the Apple menu.
2. Expand the Software section and select Installations.
3. Click on the Software Name column header to sort the list alphabetically.
4. Look for “Incompatible Kernel Extension Configuration Data.”
5. If the most recent version installed is 3.28.1, then follow the steps below.

And here’s how to fix the issue if you can connect to a Wi-Fi network:

1. Open the Terminal app.
2. Type this command to update to the current version of the “Incompatible Kernel Extension Configuration Data” kernel extension:sudo softwareupdate --background
3. Quit Terminal and restart your Mac.

Here’s how to fix the problem if you can’t connect to Wi-Fi:

1. Follow the instructions to restart your Mac in OS X Recovery. After your Mac restarts, go to step 2.
2. Select Disk Utility from the list of OS X Utilities.
3. Select your drive from the list of internal drives in the sidebar. The default name is “Macintosh HD.” Your drive might have a different name or location, if you renamed or moved it.
4. If the drive name is gray, then your drive might be protected by FileVault. Select File > Unlock from the Disk Utility menu,  and enter your FileVault password.
5. Select File > Mount in Disk Utility  to mount your drive, if it’s not already mounted.
6. Quit Disk Utility. If you’d like to be able to copy and paste the command required in Step 8, select Get Help Online from the OS X Utilities list to open Safari and view this article on Apple’s support site at support.apple.com/kb/HT6672. Quit Safari before you go to the next step.
7. Launch the Terminal app from Utilities > Terminal.
8. Type (or copy and paste) this command as one line in Terminal. In the example below, the drive name is “Macintosh HD,” and there’s a space between Macintosh and HD. If your Mac’s drive name is different, adjust the text:rm -rf “/Volumes/Macintosh HD/System/Library/Extensions/AppleKextExcludeList.kext”
9. Quit the Terminal app.
10. Select Restart from the Apple menu.
11. After your Mac restarts, your Ethernet connection should work.
12. Open the Terminal app and type this command to update to the current version of the “Incompatible Kernel Extension Configuration Data” kernel extension:sudo softwareupdate --background
13. Quit Terminal and restart your Mac.

Once your Mac is back up and running, Ethernet connectivity should be back. Apple is expected to rollout another security update without this issue in the coming days, but unfortunately, this is yet another example of Apple rolling out buggy software that breaks important features.