* Drupal Views bulk operations 6.x-1.4 and prior
Views Bulk Operations augments Views by allowing bulk operations to be executed on the nodes and users displayed by a view. It does so by showing a checkbox in front of each item, and adding a select box containing operations that can be applied on the selected items.
In some circumstances, a malicious user could use Views Bulk Operation to cause user 0 (the anonymous user) to be deleted. The effects of deleting user 0 vary depending on the system configuration and the use of other contributed modules, ranging from trivial errors to significant loss of functionality.
The risk is mitigated by the fact that a malicious user would need permission to a view that lets him/her manage users through Views Bulk Operations in order to exploit this vulnerability