Draytek Vigor2920 User Manual page 157

The reminder as regards concern about Firewall and UPnP
Can't work with Firewall Software
Enabling firewall applications on your PC may cause the UPnP function not working
properly. This is because these applications will block the accessing ability of some network
ports.
Security Considerations
Activating the UPnP function on your network may incur some security threats. You should
consider carefully these risks before activating the UPnP function.
The UPnP function dynamically adds port mappings on behalf of some UPnP-aware
applications. When the applications terminate abnormally, these mappings may not be
removed.
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Some Microsoft operating systems have found out the UPnP weaknesses and hence
you need to ensure that you have applied the latest service packs and patches.
Non-privileged users can control some router functions, including removing and
adding port mappings.
147 Vigor2920 Series User's Guide