What found the attack ?
I would have though that this exploit would have been handled by network Shield (in which case it wouldn’t have got on to your system) if not by your firewall, which is ?

What is the infected file name (if found on your system), where was it found e.g. (C:\windows\system32\infected-file-name.xxx) ?
Check the avast! Log Viewer (right click the avast ‘a’ icon), Warning section, this contains information on all avast detections. This applies to all detections on your system or Internet IP address.