The default configuration of NCSA Telnet package for Macintosh and PC enables FTP, even though it does not include an "ftp=yes" line, which allows remote attackers to read and modify arbitrary files.

Heap-based buffer overflow in the envoptadd function in telnet.c for various BSD-based Telnet clients allows remote attackers to execute arbitrary code via responses that contain a large number of characters that require escaping, which consumers more memory than allocated.

Buffer overflow in the slcaddreply function in various BSD-based Telnet clients, when handling LINEMODE suboptions, allows remote attackers to execute arbitrary code via a reply with a large number of Set Local Character (SLC) commands.