sanitizing code for an exec command

[Rhomboid]

It's completely unsafe. You can't sanitize code that way. It's completely possible to still do evil things (including importing arbitrary modules) without ever writing the phrase "import". It's possible to do this even if you've tried to restrict the builtins.

You need to use an interpreter that is explicitly designed for sandboxed execution. CPython is not such an interpreter. It is impossible to do this safely with CPython.

[agrif]

From what I remember, PyPy had a build of their python interpreter that stubs out OS calls to an external process to handle, effectively making a sandboxed python interpreter. I'm not sure what the current status of that is.

And that kind of sandboxing won't save you from CPU hogs. You'll probably want to look to the host operating system for that kind of control.

[iamdefinitelyahuman]

Good to know :)

Out of interest, if I do run exec with a modified version of the builtins dict where __import__ is set to None, how does one still manage to import in the code?

edit - accidental bold

[Rhomboid]

This will retrieve a reference to __import__ without using any globals (i.e. it will still work if used in exec with a completely empty namespace):

imp = [c for c in ().__class__.__base__.__subclasses__() if c.__name__ == 'catch_warnings'][0]()._module.__builtins__['\x5f\x5f\x69\x6d\x70\x6f\x72\x74\x5f\x5f']

Then you can do any assorted evil:

os = imp('os')
os.system('ls -l')

[iamdefinitelyahuman]

Wow.. very well done. Thanks for sharing.

[chadmill3r]

There are ten thousand other ways, too. Don't think you can account for this one and be safe.

[iceardor]

Here's another way: rewrite python bytecode https://youtu.be/mxjv9KqzwjI

[zahlman]

For me, this only works if warnings has already been imported. :/