The authors present a technique that uses the properties of the Universal Plug and Play (UPnP) protocol to get specific IPv4 hosts to divulge their IPv6 address. This allows us to enumerate a particular subset of active IPv6 hosts which can then be scanned. We performed comparative scans of discovered hosts on both IPv4 and IPv6 and presented the results and analysis. Our findings show that this technique is valid and that there are significant security discrepancies in filtering between the two interfaces of these hosts.”]
Source: https://blog.talosintelligence.com/2019/03/ipv6-unmasking-via-upnp.html