    def test_crlf_injection
      smtp = Net::SMTP.new 'localhost', 25
      smtp.instance_variable_set :@socket, FakeSocket.new

      assert_raise(ArgumentError) do
        smtp.mailfrom("foo\r\nbar")
      end

      assert_raise(ArgumentError) do
        smtp.mailfrom("foo\rbar")
      end

      assert_raise(ArgumentError) do
        smtp.mailfrom("foo\nbar")
      end

      assert_raise(ArgumentError) do
        smtp.rcptto("foo\r\nbar")
      end
    end
The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.