The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-11:01.mountd.asc

Upgrade your system to the appropriate stable release or security branch dated after the correction date https://secure1.securityspace.com/smysecure/catid.html?in=FreeBSD-SA-11:01.mountd.asc

The mountd(8) daemon services NFS mount requests from other client machines. When mountd is started, it loads the export host addresses and options into the kernel using the mount(2) system call. While parsing the exports(5) table, a network mask in the form of -network=netname/prefixlength results in an incorrect network mask being computed if the prefix length is not a multiple of 8. For example, specifying the ACL for an export as -network 192.0.2.0/23 would result in a netmask of 255.255.127.0 being used instead of the correct netmask of 255.255.254.0.