[Python-Dev] XML DoS vulnerabilities and exploits in Python

[Antoine Pitrou]

On Wed, 20 Feb 2013 18:21:22 -0500
Donald Stufft <donald.stufft at gmail.com> wrote:
> On Wednesday, February 20, 2013 at 6:08 PM, Antoine Pitrou wrote:
> > > It's not a distributed DoS issue, it's a severe DoS vulnerabilities. A
> > > single 1 kB XML document can kill virtually any machine, even servers
> > > with more than hundred GB RAM.
> > > 
> > 
> > Assuming an attacker can inject arbitrary XML. Not every XML document
> > is loaded from the Internet.
> 
> Even documents not loaded from the internet can be at risk. Often times
> security breaches are the result of a chain of actions. You can say "I'm
> not loading this XML from the internet, so therefore I am safe" but then
> you have another flaw (for example) where you unpack a zip file
> without verifying there are not absolute paths and suddenly your xml file has
> been replaces with a malicious one.

Assuming your ZIP file is coming from the untrusted Internet, indeed.
Again, this is the same assumption that you are grabbing some important
data from someone you can't trust.

Just because you are living in a Web-centric world doesn't mean
everyone does. There are a lot of use cases which are not impacted by
your security rules. Bugfix releases shouldn't break those use cases,
which means the security features should be mostly opt-in for 2.7 and
3.3.

Regards

Antoine.