Imagine using a LIVE CD with a critical vulnerability in Electrum!
You mean like Tails?
[1] Another question is wether this is somehow important?
As far as i know tails is designed to stay offline. If this is correct and people use tails how it is supposed to be used, i can't seem to find an attack vector which makes use of the found vulnerability.
This, of course, is no excuse for using an old (unpatched) version. But this still does not expose one to a higher risk.
If you can think of any attack vector which might exploit this vulnerability (in any way), i'd be happy being enlighten.