There are a couple of things you can look at - it matters what your servers are using and how they are set up.

You can either look into changing on server B your /etc/hosts.allow and/or /etc/hosts.deny files (if you are using tcp wrappers), OR, you can shutdown the rsh services in /etc/inetd.conf. See the man page for inetd.conf and inetd.

You can also look to see if /etc/hosts.equiv exist - it may be granting the access there.

Before changing anything - you need to understand what it may do to something that IS okay between these servers (maybe remote copy is needed so turning off all rsh services would not be the way to go).