Hi!
We're currently investigating this issue, but so far it doesn't seem to impact Webnodes directly. IIS uses Microsoft's own SSL implementation, so it is not directly affected. We're awaiting a response from Advanced Intellect regarding the email component used in Webnodes, but we have no indication that it uses OpenSSL.
We'll update this thread when we know more.
For more information, this is a good resource:
http://www.troyhunt.com/2014/04/everything-you-need-to-know-about.html