Well, the Ubuntu part came from HD Moore [1]. I haven't been able to confirm it on my Ubuntu 12.04 virtual machine instance though, nor does my virtual machine appear to trigger the bug using the CVE-2012-2122 checker [2].
But, that is just my single VM instance and I would assume HD Moore knows what he is doing.
Yep, if you're blocking remote hosts to authenticate on 3306 (or any other port you're running mysqld on) you're safe. The attacking host can't authenticate itself, so it's unable to exploit this bug.
But, that is just my single VM instance and I would assume HD Moore knows what he is doing.
[1] http://pastie.org/private/903voijkkz8nmde3yqj4rw
[2] http://pastie.org/4064638