Microsoft Windows NT 3.5.1 SP2/3.5.1 SP3/3.5.1 SP4/3.5.1 SP5/4.0/4.0 SP1/4.0 SP2/4.0 SP3/4.0 SP4/4.0 SP5 - TelnetD
source: https://www.securityfocus.com/bid/140/info
A vulnerability exists within Microsoft's Telnetd daemon which allows a denial of service condition. The popular scanning tool, Nmap 2.01 or later can crash telnetd services when using the SYN scanning flag (-sS).
nmap -sS -p 23 <target>