metasploit-gs/lib/net/ssh/authentication/methods/hostbased.rb

require 'net/ssh/authentication/methods/abstract'

module Net
  module SSH
    module Authentication
      module Methods

        # Implements the host-based SSH authentication method.
        class Hostbased < Abstract
          include Constants

          # Attempts to perform host-based authorization of the user by trying
          # all known keys.
          def authenticate(next_service, username, password=nil)
            return false unless key_manager

            key_manager.each_identity do |identity|
              return true if authenticate_with(identity, next_service,
                username, key_manager)
            end

            return false
          end

          private

            # Returns the hostname as reported by the underlying socket.
            def hostname
              session.transport.socket.client_name
            end

            # Attempts to perform host-based authentication of the user, using
            # the given host identity (key).
            def authenticate_with(identity, next_service, username, key_manager)
              debug { "trying hostbased (#{identity.fingerprint})" }
              client_username = ENV['USER'] || username

              req = build_request(identity, next_service, username, "#{hostname}.", client_username)
              sig_data = Buffer.from(:string, session_id, :raw, req)

              sig = key_manager.sign(identity, sig_data.to_s)

              message = Buffer.from(:raw, req, :string, sig)

              send_message(message)
              message = session.next_message

              case message.type
                when USERAUTH_SUCCESS
                  info { "hostbased succeeded (#{identity.fingerprint})" }
                  return true
                when USERAUTH_FAILURE
                  info { "hostbased failed (#{identity.fingerprint})" }
                  return false
                else
                  raise Net::SSH::Exception, "unexpected server response to USERAUTH_REQUEST: #{message.type} (#{message.inspect})"
              end
            end

            # Build the "core" hostbased request string.
            def build_request(identity, next_service, username, hostname, client_username)
              userauth_request(username, next_service, "hostbased", identity.ssh_type,
                Buffer.from(:key, identity).to_s, hostname, client_username).to_s
            end

        end

      end
    end
  end
end