How is it blocked? Filescanner or behavior shield?
An ordinary detection, i.e. file scanner / mail scanner / web shield / ...
Are morphed variants also detected or do the patterns have to match exactly?
Well, some patterns always have to be matched - otherwise the exploit wouldn't work at all
But yes, even currently unseen variants are detected.
So, are we safe against unknown yet to be released variants?
Nobody can say that, of course - it's impossible to say what modifications appear in the future.
Does Avast Community IQ come into play here?
Partially yes. The thing is that this whole "vulnerability" is not really a bug - but rather a feature. Some users have basically the same non-malicious link files on their disks; some printer/modem installers create them. So, we use the community submissions to (silently) check for false alarms before making the detection too general (i.e. covering more than we really want).