Several distributors of the BSD version of the Telnet protocol have released patches for a critical bug that could cause system-hijack attacks.
According to iDefense, remote exploitation of a buffer overflow vulnerability in multiple Telnet clients could allow the execution of arbitrary code.
The Telnet protocol allows virtual network terminals to be connected to over the Internet. The initial description of the telnet protocol was given in RFC854 in May 1983. Since then there have been many extra features added including encryption.
Successful exploitation of this vulnerability could allow an attacker to execute arbitrary commands in the context of the user who launched the Telnet client, says iDefense.
iDefense has confirmed the existence of the vulnerability in the Telnet client included in the Kerberos V5 Release 1.3.6 package and the client included in the SUNWtnetc package of Solaris 5.9. According to the advisory, it is suspected that most BSD based Telnet clients are affected by this vulnerability.
Advisories and patches have been issued by FreeBSD, MIT (Kerberos), Red Hat, and Sun among others.