One point to add, I don’t use any external USB drive.
I open this thread is just to assure other users that if you
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never hacked your WD MyCloud
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never installed third party items
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no external drive attached to MyCloud
It should be okay to go ahead to update this firmware. It is true that not all firmwares are good, the infamous buggy [Deleted - Trancer] first release 4.X firmware a few months ago is a good example. But this one should be okay, especially it closed the bash shell bug.
The only one thing I tuned by myself is on the router side. I give a fix IP address to the MyCloud, so the Windows desktop shortcut will always point to the MyCloud IP address correctly, even the MyCloud reboot after upgrade.
Networking with Windows or Mac is never a fool proof job. If anyone gets some problems after upgrade, I suggest an old way to fix the problems like in Windows 3.X era - Uninstall WD softwares, reboot your Windows box (or Mac), then install WD softwares again. Hope this helps!