[Full-disclosure] Vulnerability in reCAPTCHA for Drupal

["MustLive" <mustlive@xxxxxxxxxxxxxxxxxx>]

Hello list!

I want to warn you about Insufficient Anti-automation vulnerability in
reCAPTCHA for Drupal.

In project MoBiC in 2007 I already wrote about bypassing of reCaptcha for
Drupal (http://websecurity.com.ua/1505/). This is new method of bypassing
reCaptcha for Drupal.

-------------------------
Affected products:
-------------------------

Vulnerable are all versions of reCAPTCHA plugin for Captcha module versions
before 6.x-2.3 and 7.x-1.0.

----------
Details:
----------

Insufficient Anti-automation (WASC-21):

In different forms in Drupal the vulnerable captcha-plugin reCAPTCHA is
using. Drupal's Captcha module is vulnerable itself, so besides reCAPTCHA
other captcha-plugins also can be vulnerable (at that this exploit is a
little different from exploit for default Captcha module for Drupal).

For bypassing of captcha it's needed to use correct value of captcha_sid, at
that it's possible to not answer at captcha (captcha_response) or set any
answer. This method of captcha bypass is described in my project Month of
Bugs in Captchas (http://websecurity.com.ua/1498/). Attack is possible while
this captcha_sid value is active.

Vulnerabilities exist on pages with forms: http://site/contact,
http://site/user/1/contact, http://site/user/password and
http://site/user/register. Other forms where reCAPTCHA is using also will be
vulnerable.

Exploit:

http://websecurity.com.ua/uploads/2011/Drupal%20reCAPTCHA%20bypass.html

------------
Timeline:
------------

2010.12.11 - announced at my site.
2010.12.14 - informed reCAPTCHA developers.
2010.12.14 - informed Google (reCAPTCHA owner).
2011.02.16 - disclosed at my site.

I mentioned about this vulnerability at my site
(http://websecurity.com.ua/4752/).

Best wishes & regards,
MustLive
Administrator of Websecurity web site
http://websecurity.com.ua


_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/