A security issue and some vulnerabilities have been reported in Drupal, which can be exploited by malicious users to disclose sensitive information and bypass certain security restrictions, and by malicious people to disclose sensitive information and conduct cross-site scripting attacks.

1) Certain unspecified input passed via the URL to the Forum module is not properly sanitised before being returned to the user. This can be exploited to execute arbitrary HTML and script code in a user's browser session in context of an affected site.

2) A vulnerability is caused due to users being able to change their signature in a format that should not be accessible to them. If the administrator changed the comment style to a more powerful format, this can be exploited to e.g. conduct script insertion attacks and potentially inject and execute arbitrary PHP code.

3) A security issue is caused due to Drupal generating a page including URLs containing sensitive information (e.g. slightly incorrect username and password) after a failed login attempt of an anonymous user. If the user follows said URLs, this information could leak to other pages via the HTTP "referer" header.

Note: If page caching is enabled, this can further be exploited to disclose the username and password by e.g. tricking an anonymous user into following a specially crafted URL.

Solution
Update to version 6.13 or apply the patch.
Further details available to Secunia VIM customers

Provided and/or discovered by
1) Mark Piper of Catalyst IT Ltd, Sven Herrmann, and Brandon Knight
2) Gerhard Killesreiter of the Drupal security team
3) Sumit Datta

Changelog
Further details available to Secunia VIM customers

Original Advisory
SA-CORE-2009-007:
http://drupal.org/node/507572

Deep Links
Links available to Secunia VIM customers