Problem with Drupal 6.16

Security fixes in 6.16:

Installation cross site scripting
A user-supplied value is directly output during installation allowing a malicious user to craft a URL and perform a cross-site scripting attack. The exploit can only be conducted on sites not yet installed.

Open redirection
The API function drupal_goto() is susceptible to a phishing attack. An attacker could formulate a redirect in a way that gets the Drupal site to send the user to an arbitrarily provided URL. No user submitted data will be sent to that URL.

Locale module cross site scripting
Locale module and dependent contributed modules do not sanitize the display of language codes, native and English language names properly. While these usually come from a preselected list, arbitrary administrator input is allowed. This vulnerability is mitigated by the fact that the attacker must have a role with the 'administer languages' permission.

Blocked user session regeneration
Under certain circumstances, a user with an open session that is blocked can maintain his/her session on the Drupal site, despite being blocked.

A couple of things, which aren't nice in this security fix:

Drupal 6.16 unfortunately introduced a change which makes it incompatible with PHP 4 in itself. Apply the one-line change explained in http://drupal.org/node/732096#comment-2679226 until a new Drupal release comes out which will include a fix for this issue.

If you use Devel Themer module which comes with Devel package you're in troubles too, because this release brake Devel Themer functionality. The issue on drupal.org is resolved now, but in a strange way - you have to use Devel Themer separate module to achieve the same functionality.