View online: https://drupal.org/node/2081887

  * Advisory ID: PSA-2013-001
  * Project: Drupal core [1]
  * Version: 6.x, 7.x
  * Date: 2013-September-04
  * Security risk: Not critical [2]
  * Exploitable from: Remote
  * Vulnerability: Information Disclosure

-------- DESCRIPTION  
---------------------------------------------------------

This is a public service announcement regarding possible insertion of hidden
links in comments using core CSS selectors within filtered HTML Text formats
("Input formats" in Drupal 6). Drupal core provides several CSS selectors
that, by design, hide elements on the page. Using these selectors it is
possible to create links to third-party websites that are hidden within a
comment. This technique has been observed on live production websites.

Drupal core provides mechanisms that sanitize user submitted links by adding
a rel="nofollow" attribute. This feature can be enabled for Drupal 7 sites at
admin/config/content/formats/filtered_html and for Drupal 6 sites at
admin/settings/filters/1/configure. Note that these paths are for the default
formats provided with core. Your site may define custom formats which should
be reviewed and updated as well.

Careful moderation of user submitted comments is always advised.
Additionally, automated comment moderation tools may help to mitigate and
flag these malicious comment submissions.


-------- SOLUTION  
------------------------------------------------------------

Review user-submitted content on your site to see if untrusted users have
posted content that includes classes. Review those classes to see if they
will hide unwanted content.
-------- REPORTED BY  
---------------------------------------------------------

  * Aaron Weiss [3]

-------- COORDINATED BY  
------------------------------------------------------

  * David Stoline [4] of the Drupal Security Team

-------- CONTACT AND MORE INFORMATION  
----------------------------------------

The Drupal security team can be reached at security at drupal.org or via the
contact form at http://drupal.org/contact [5].

Learn more about the Drupal Security team and their policies [6], writing
secure code for Drupal [7], and securing your site [8].


[1] http://drupal.org/project/drupal
[2] http://drupal.org/security-team/risk-levels
[3] http://drupal.org/user/745366
[4] http://drupal.org/user/329570
[5] http://drupal.org/contact
[6] http://drupal.org/security-team
[7] http://drupal.org/writing-secure-code
[8] http://drupal.org/security/secure-configuration