Microsoft NT "un-removable user" Vulnerability.

[John Lange <lists () DARKCORE NET>]

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