Cisco Security Advisory – A specifically crafted Transmission Control Protocol (TCP) connection to a telnet or reverse telnet port of a Cisco device running Internetwork Operating System (IOS) may block further telnet, reverse telnet, Remote Shell (RSH), Secure Shell (SSH), and in some cases Hypertext Transport Protocol (HTTP) access to the Cisco device. Telnet, reverse telnet, RSH and SSH sessions established prior to exploitation are not affected. This vulnerability affects all Cisco devices that permit access via telnet or reverse telnet and are running an unfixed version of IOS.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/34186/cisco-sa-20040827-telnet.txt
Source: https://packetstormsecurity.com/files/34186/Cisco-Security-Advisory-20040827-telnet.html