Untrusted code execution

[Jon Ribbens]

On 2016-04-03, Jon Ribbens <jon+usenet at unequivocal.co.uk> wrote:
> I'd just like to say up front that this is more of a thought experiment
> than anything else, I don't have any plans to use this idea on any
> genuinely untrusted code. Apart from anything else, there's the
> denial-of-service issue.
>
> That said, is there any way that the following Python 3.4 code could
> result in a arbitrary code execution security hole?
>
>     tree = compile(untrusted_code, "<script>", "eval", ast.PyCF_ONLY_AST)
>     for node in ast.walk(tree):
>         if (isinstance(node, ast.Name) and node.id.startswith("_") or
>             isinstance(node, ast.Attribute) and node.attr.startswith("_")):
>                 raise ValueError("Access to private values is not allowed.")
>     namespace = {"__builtins__": {"int": int, "str": str, "len": len}}
>     print(eval(compile(tree, "<script>", "eval"), namespace))

Nobody has any thoughts on this at all?