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Re: Microsoft NT "un-removable user" Vulnerability.
From: Steve <steve () SECURESOLUTIONS ORG>
Date: Tue, 5 Sep 2000 20:07:39 -0600

Hash: SHA1

Microsoft NT “un-removable user” Vulnerability.

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

Could not reproduce at SP6a.

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.

What custom User Manager are you using.  The normal interface
provided does not allow this, nor do a few of the more popular
add-ins to NT.

The problem exists because the integrity checking on the userIDs
occurs at the GUI level and not on the system itself.

I agree that this *COULD* be an issue but not a likely one.

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.

Yes, but a simple net user ~testuser;") /delete will take care of

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.

Incorrect.  Net user /delete works just fine.

Credit: This vulnerability was discovered by Jeff Also while
developing a web based User Management interface.

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.

I fail to see how this is a vulnerability.  If a malicious user
already has "rooted" the NT box, why would he be stupid enough to add
a user to the system that would be obviously out of place.  Why would
he not add a machine name ID, or even a generic username and hope the
sys-admin doesn't notice.  Seeing the existance of ~testuser;") would
be a dead give-away that something is going on.


Steve Manzuik
Moderator - Win2K Security Advice

Version: PGPfreeware 6.5.3 for non-commercial use


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