Exploit for a security hole in the pickle module for Python versions <= 2.1.x

[Jeff Epler]

On Thu, Jul 18, 2002 at 09:07:53PM +0200, Dieter Maurer wrote:
> Jeff Epler <jepler at unpythonic.net> writes on Wed, 17 Jul 2002 07:47:14 -0500:
> > Exploit for a security hole in the pickle module for Python versions <= 2.1.x
> Thank you for the precise problem statement!
> > ...
> > Because a "class constructor" is
> > simply a callable object,
> > a pickle can be written that names any function
> > and gives it arbitrary arguments.
> But this need not be the case!
> 
>    A "class constructor" is quite a special "function".
>    Its "type" is "ClassType" (at least until Python 2.2).

This test would "work" against the exploit I posted.  However, this test
is not implemented in any version of Python.  Furthermore, there are
classes which are unsafe to instantiate.  For instance, popen2.Popen3
is as dangerous a constructor as os.system is a function.

>>> type(popen2.Popen3)
<type 'class'>

That's the reason the "safe for unpickling" requirement was added.

Jeff