nmap -p- IPADDRESSHERE
shows no opened ports for a router from public interface (router is an openwrt machine). It drops all ICMP and only has IPv4 address (the only thing that it runs on public interface is an sshd server, but it's port knocked, so cannot be seen).
If we don't count the clients behind this router, and the attacker could be anyone (but only through public interface, so it's coming from the "internet") so Theoretically how much chance does the attacker has to crack/hack (whatever its used to be called to get a shell on the router, or do nasty things in it)?
Would it be hard for an attacker to get into this router, or are there any known methods?