Sometimes you have to rebuild ports due to a library update. But if there are vulnerabilities known for that ports then
make will bail out with an error message and refuse to build the port. Instead it gives you the advice to update or deinstall the port which is good advice but sometimes just not possible.
If you want to force the build of that port you can use the flag
make or if you use
portmaster to manage your ports you can pass it through the
-m flag, like this:
# portmaster -m DISABLE_VULNERABILITIES=yes -a
This would update all installed ports while ignoring possible existing vulnerabilities for each port.
Please use this only as a last resort or if you know what you are doing!