A weakness, a security issue, and multiple vulnerabilities have been reported in Drupal, which can be exploited by malicious users to disclose sensitive information, bypass certain security restrictions, and cause a DoS (Denial of Service).

1) A weakness is caused due to inefficient text matching pattern and can be exploited to exhaust memory or cause a high CPU load via specially crafted strings passed to the filter system e.g. when posting comments or forum topics.

2) An error due to the application not properly validating the destination for submitted forms can be exploited to redirect submission of sensitive data (e.g. login credentials) to a malicious website.

3) An error due to the application not properly validating user permissions when displaying the forum overview page can be exploited to expose certain metadata of unpublished forum posts.

4) An error due to the application not properly validating user access to cached derivatives of users' private images can be exploited to gain access to derivatives of otherwise restricted images.

5) An error due to the application not properly validating user access to each node in the list of nodes can be exploited to gain access to otherwise restricted nodes.

Successful exploitation of this vulnerability requires the "view content overview" permission and a contributed node access module.

The vulnerabilities are reported in 7.x versions prior to 7.13.

Solution
Update to version 7.13.

Provided and/or discovered by
2) Katsuhiko Nakanishi via JVN and Károly Négyesi, Drupal Security Team.

The vendor credits:
1) Jay Wineinger and Lin Clark
3) Glen W
4) frega, Andreas Gonell, Jeremy Meier, and Xenza
5) Jennifer Hodgdon

Changelog
Further details available to Secunia VIM customers

Original Advisory
DRUPAL-SA-CORE-2012-002:
http://drupal.org/node/1557938

JVN:
http://jvn.jp/en/jp/JVN45898075/index.html
http://jvndb.jvn.jp/en/contents/2012/JVNDB-2012-000045.html

Deep Links
Links available to Secunia VIM customers