Winbox vulnerability: please upgrade

Yeah, that configuration is not secure. Wide open to the internet and attackers.
At least missing a couple block rules in the firewall filter. For example:

/ip firewall filter
add action=accept chain=forward in-interface=ether1 connection-state=established,related
add action=accept chain=input in-interface=ether1 connection-state=established,related
add action=drop chain=forward in-interface=ether1
add action=drop chain=input in-interface=ether1

But suggest you read the manual page about securing your router: https://wiki.mikrotik.com/wiki/Manual:Securing_Your_Router

No they can not access the linux operating system of the router, unless you have rooted the router yourself already. Which you really should not do.
Unless you were running a version of RouterOS that is older than v6.38.5, see: http://forum.mikrotik.com/t/urgent-security-advisory/117944/1

I suggest you email support@mikrotik.com with your license issue.