[Python-Dev] Cookie.py security

[Fredrik Lundh]

jeremy wrote:
> I would guess that pickle makes attacks easier: It has more features,
> e.g. creating instances of arbitrary classes (provided that the attacker
> knows what classes are available).

well, if not else, he's got the whole standard library to
play with...

:::

(I haven't looked at the cookie code, so I don't really know
what I'm talking about here)

cannot you force the user to pass in a list of valid classes to
the cookie constructor, and use a subclass of pickle.Unpickler
to get a little more control over what's imported:

    class myUnpickler(Unpicker):
        def __init__(self, data, classes):
            self.__classes = classes
            Unpickler.__init__(self, StringIO.StringIO(data))
        def find_class(self, module, name):
            for cls in self.__classes__:
                if cls.__module__ == module and cls.__name__ == name:
                    return cls
            raise SystemError, "failed to import class"

> But neither marshal nor pickle is safe.  It is possible to cause a
> core dump by passing marshal invalid data.  It may also be possible to
> launch a stack overflow attack -- not sure.

</F>