Debian Security Advisory DSA 389-1 – ipmasq below version 3.5.12 creates improper filtering rules that will allow traffic on an external interface to route to an internal host via forwarding.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/31686/DSA-389-1
Source: https://packetstormsecurity.com/files/31686/DSA-389-1.html