[Python-Dev] Challenge: Please break this! (a.k.a restricted mode revisited)

Jon Ribbens jon+python-dev at unequivocal.co.uk
Fri Apr 8 11:44:15 EDT 2016

On Fri, Apr 08, 2016 at 05:21:38PM +0200, Arthur Darcet wrote:
>    If i'm not mistaken, this breaks out:
>    > exec('open("out", "w").write("a")', {})
>    because if the second argument of exec does not contain a __builtins__
>    key, then a copy of the original builtins module is inserted:
>    https://docs.python.org/3/library/functions.html#exec

Ah, that's a good point. I did think allowing eval/exec was a bit
ambitious. I've updated it to disallow passing namespace arguments to

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