[ SOURCE: http://www.secureroot.com/security/advisories/9684957953.html ]

Microsoft NT "un-removable user" Vulnerability.



Vulnerable: Tested on NT4 SP4. All version of NT are thought to be

vulnerable.



A vulnerability exists in the Microsoft Windows NT operating system in which

a userid can be added which conations special characters which are normally

not allowed. These special userids can not be removed using the normal user

management interface as supplied from Microsoft.



The problem exists because the integrity checking on the userIDs occurs at

the GUI level and not on the system itself.



Exploit:

A malicious user can create a user with special characters (e.g.

 "testuser;") using a custom user management interface which does not

perform validation checks on the userid. It then can not be removed using

the standard WindowsNT user management interface.



This could be a significant problem if the user was maliciously added into

the Administrators group. A system scrub or another custom user management

interface would be the only way to remove the user.



Credit: This vulnerability was discovered by Jeff Also while developing a

web based User Management interface.



Reported:

---------

I advised Microsoft Security about this on 28 Aug 2000. They responded that

since they had no custom user management tools, they could not test this

vulnerability.



John Lange

johnl@clearoption.com

Network Administrator

ClearOption Technologies