Permissions, Privileges, and Access Controls
components/com_user/models/reset.php in Joomla! 1.5 through 1.5.5 does not properly validate reset tokens, which allows remote attackers to reset the "first enabled user (lowest id)" password, typically for the administrator.
CWE-264 - Permissions Privileges and Access Controls
CWE 264 (permissions, privileges, and access controls) is not a weakness in and of itself, rather it is a category of weaknesses related to the management of permissions, privileges, and other security features used to perform access control. If not addressed, the weaknesses in this category allow attackers to gain privileges for an unintended sphere of control, access sensitive information, and execute arbitrary commands.