Security Update Breaks Ethernet Port on iMacs and MacBook Pros [Updated]

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As reported on the MacRumors forums and Reddit, a recent Apple security update has disabled the ethernet port on some iMacs and MacBook Pros. zorinlynx writes:
This software update was pushed via the silent "security updates" to my iMac today:

031-51913 | Incompatible Kernel Extension Configuration Data 3.28.1

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.
The experience was mirrored by several other readers. Apple appears to have already replaced the faulty update, but there doesn't appear to be an obvious solution for those affected.

Update 9:30 PM: Apple has posted a support document outlining how to tell whether your system has the bad update installed and how to update to the fixed version 3.28.2.

Article Link: Security Update Breaks Ethernet Port on iMacs and MacBook Pros [Updated]
 

pat500000

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Jun 3, 2015
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my 2 ethernet ports died.
I meant, it's not just iMacs and MacbookPro..., MacPro also affected.
Didn't know.....but wow....Apple definitely shouldn't be in computer business ...
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Shared storage rely on it
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I have same computer. And it's broke
This is bad on apple side.
 

duncandsorderly

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Jun 26, 2013
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>>Do people still use ethernet in 2016??<<

yes. it's faster, more secure, more reliable in wireless-congested city apartments &... it works, whereas wifi can be flakey on a 15" rMBP if you also have BT enabled.

in re the question as to how to fix this once the security update has broken your ethernet driver... ("but there doesn't appear to be an obvious solution for those affected."), if you're not using TM & can't roll back, go somewhere where you can use wifi & apply the new version of the patch. let me know if I'm overcomplicating things here.
 

bpd115

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broke my nMP 2013 too
So I was adding a time capsule to my network last night and I inactivated my Ethernet port. (I'm not getting into the whys, not important)

When I rebooted my retina iMac, I had no Ethernet.

System profiler said no PCI Ethernet installed.

Thought it was a fluke, so I booted via Internet recovery and I was getting an Ethernet interface there.

So I just reinstalled 10.11 and called it a night.

Working fine now. (As an aside, all your data will still be there, you just have to do the 10.11 to 10.11.3 updates.)

Interesting.