The remote host is missing an update to the system as announced in the referenced advisory FreeBSD-SA-09:05.telnetd.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-09:05.telnetd.asc

The FreeBSD telnet daemon, telnetd(8), implements the server side of the TELNET virtual terminal protocol. It has been disabled by default in FreeBSD since August 2001, and due to the lack of cryptographic security in the TELNET protocol, it is strongly recommended that the SSH protocol be used instead. The FreeBSD telnet daemon can be enabled via the /etc/inetd.conf configuration file and the inetd(8) daemon. The TELNET protocol allows a connecting client to specify environment variables which should be set in any created login session this is used, for example, to specify terminal settings. In order to prevent environment variable based attacks, telnetd(8) scrubs its environment however, recent changes in FreeBSD's environment-handling code rendered telnetd's scrubbing inoperative, thereby allowing potentially harmful environment variables to be set.