regex infinite loop with 100% cpu use in django.forms.fields.email_re - DOS hole?

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davisd

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Oct 9, 2009, 2:13:23 PM10/9/09
to Django users
After hours of debugging, I found that:

from django.forms.fields import email_re
email_re.match
('viewx3dte...@yahoo.comx26latlngx3d15854521645943074058')

will cause CPU to shoot up 100% and the process will hang forever.

Since this is the regex used to validate EmailField on forms, won't
this DOS a live site?

Where should I report this?

Is there a better way to validate an email address?

davisd

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Oct 9, 2009, 2:37:09 PM10/9/09
to Django users
Ok! I just confirmed this, I took down a live server! (On of my own)

All I had to do was put the email address in the contact form.

-David

On Oct 9, 1:13 pm, davisd <davisd.dav...@gmail.com> wrote:
> After hours of debugging, I found that:
>
> from django.forms.fields import email_re
> email_re.match
> ('viewx3dtextx26q...@yahoo.comx26latlngx3d15854521645943074058')

Juan Hernandez

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Oct 9, 2009, 3:15:21 PM10/9/09
to django...@googlegroups.com
Take a look at mine:

In [41]: from django.forms.fields
django.forms.fields

In [41]: from django.forms.fields import email_re

In [42]: email_re.match('viewx3dte...@yahoo.comx26latlngx3d15854521645943074058')


and this is what top shows:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND          
13886 juan      20   0 17556  12m 1992 R   95  1.3   0:59.61 ipyth
on   

and stays like that for ever...

James Bennett

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Oct 9, 2009, 3:18:32 PM10/9/09
to django...@googlegroups.com
Yes.

We've confirmed the problem. We're working on a patch.

In the meantime, everybody go meditate on the documentation for how to
report security issues.


--
"Bureaucrat Conrad, you are technically correct -- the best kind of correct."

davisd

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Oct 9, 2009, 3:21:53 PM10/9/09
to Django users
Sorry for the public disclosure... I did email django security after
I posted. I'm just getting into this open source goodness and I'm not
really sure how it's supposed to operate yet.

I did consult the documentation: http://docs.djangoproject.com/en/dev/internals/contributing/

Jacob:
I'm running django from SVN
Python 2.6.2
I believe the Operating system is moot- it's all in the python.
Linux kernel 2.6.31-11, but also 2.6.18.8 -

I'm wondering if a multithreaded webserver setup would be more guarded
against this sort of thing?

Karen Tracey

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Oct 9, 2009, 4:05:16 PM10/9/09
to django...@googlegroups.com
On Fri, Oct 9, 2009 at 3:21 PM, davisd <davisd...@gmail.com> wrote:

I'm wondering if a multithreaded webserver setup would be more guarded
against this sort of thing?


Yeah, but.  When I tried this on my own production server (Apache/mod_wsgi) the process handling the request that caused the problem was killed after the deadlock timeout was reached. But deadlock timeout can't really protect you from a determined denial of service attack, so it's still a problem in Django.

Karen

Jacob Kaplan-Moss

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Oct 9, 2009, 5:59:14 PM10/9/09
to django...@googlegroups.com
Just as an update for anyone following this thread:

This was indeed a security exploit, and it has been fixed. See
http://www.djangoproject.com/weblog/2009/oct/09/security/ for details.

Jacob

Tom Evans

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Oct 12, 2009, 5:00:31 AM10/12/09
to django...@googlegroups.com
On Fri, 2009-10-09 at 12:21 -0700, davisd wrote:
> Sorry for the public disclosure... I did email django security after
> I posted. I'm just getting into this open source goodness and I'm not
> really sure how it's supposed to operate yet.
>
> I did consult the documentation: http://docs.djangoproject.com/en/dev/internals/contributing/
>
> Jacob:
> I'm running django from SVN
> Python 2.6.2
> I believe the Operating system is moot- it's all in the python.
> Linux kernel 2.6.31-11, but also 2.6.18.8 -
>
> I'm wondering if a multithreaded webserver setup would be more guarded
> against this sort of thing?
>

This bug has no effect on FreeBSD systems I've tested, so it looks like
it is OS specific.

FreeBSD 7.0, 7.1, 7.2 + python 2.5.4 work fine.

> $ time python -c "from django.forms.fields import email_re; email_re.match('viewx3dte...@yahoo.comx26latlngx3d15854521645943074058'); import django; print django.VERSION"
(1, 1, 0, 'final', 0)

real 0m0.086s
user 0m0.055s
sys 0m0.029s


Linux 2.6.27 + python 2.5.4 fails.

> $ time python -c "from django.forms.fields import email_re; email_re.match('viewx3dte...@yahoo.comx26latlngx3d15854521645943074058'); import django; print django.VERSION"
^CTraceback (most recent call last):
File "<string>", line 1, in <module>
KeyboardInterrupt

real 0m21.317s
user 0m21.173s
sys 0m0.044s


Cheers

Tom

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