Python Security Advisory PSF-2005-001 -

Guido van Rossum gvanrossum at
Thu Feb 3 16:02:03 CET 2005

Python Security Advisory

Advisory ID:  PSF-2005-001
Issue Date:   February 3, 2005
Product:      Python
Versions:     2.2 all versions, 2.3 prior to 2.3.5, 2.4
CVE Names:    CAN-2005-0089

Python is an interpreted, interactive, object-oriented programming
language. It is often compared to Tcl, Perl, Scheme or Java.

The Python development team has discovered a flaw in the
SimpleXMLRPCServer library module which can give remote attackers
access to internals of the registered object or its module or possibly
other modules.  The flaw only affects Python XML-RPC servers that use
the register_instance() method to register an object without a
_dispatch() method.  Servers using only register_function() are not

On vulnerable XML-RPC servers, a remote attacker may be able to view
or modify globals of the module(s) containing the registered
instance's class(es), potentially leading to data loss or arbitrary
code execution.  If the registered object is a module, the danger is
particularly serious.  For example, if the registered module imports
the os module, an attacker could invoke the os.system() function.

But the attack is not limited to registered object modules; for
example, the code in the Python cookbook recipe at is
vulnerable to an attack using im_func.func_globals.update which allows
reading or modifying the global variable accessList.

The Common Vulnerabilities and Exposures project ( has
assigned the name CAN-2005-0089 to this issue.

Python 2.3.5 will be released from within a few days
containing a fix for this issue.  Python 2.4.1 will be released later
this month containing the same fix.  Patches for Python 2.2, 2.3 and
2.4 are also immediately available:

- (Python 2.2)

- (Python 2.3, 2.4)

Note that these patches disable recursive traversal, potentially
resulting in reduced functionality of XML-RPC applications depending
on this feature.

--Guido van Rossum (home page:

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