Alert: Microsoft Security Bulletin - MS02-064

From: Russ (Russ.Cooper@RC.ON.CA)
Date: 10/31/02

Date:         Thu, 31 Oct 2002 00:10:47 -0500
From: Russ <Russ.Cooper@RC.ON.CA>

Windows 2000 Default Permissions Could Allow Trojan Horse Program (Q327522)

Originally posted: October 30, 2002


Who should read this bulletin: System administrators running Microsoft® Windows® 2000.

Impact of vulnerability: Trojan Horse program execution

Maximum Severity Rating: Moderate

Recommendation: Administrators should consider changing access permissions on the Windows 2000 system root directory.

Affected Software:
- Microsoft Windows 2000

Technical description:

On Windows 2000, the default permissions provide the Everyone group with Full access (Everyone:F) on the system root folder (typically, C:\). In most cases, the system root is not in the search path. However, under certain conditions - for instance, during logon or when applications are invoked directly from the Windows desktop via Start | Run - it can be.

This situation gives rise to a scenario that could enable an attacker to mount a Trojan horse attack against other users of the same system, by creating a program in the system root with the same name as some commonly used program, then waiting for another user to subsequently log onto the system and invoke the program. The Trojan horse program would execute with the user's own privileges, thereby enabling it to take any action that the user could take.

The simplest attack scenario would be one in which the attacker knew that a particular system program was invoked by a logon script. In that case, the attacker could create a Trojan horse with the same name as the system program, which would then be executed by the logon script the next time someone logged onto the system. Other scenarios almost certainly would require significantly greater user interaction - for instance, convincing a user to start a particular program via Start | Run - and would necessitate the use of social engineering.

The systems primarily at risk from this vulnerability would be workstations that are shared between multiple users, and local terminal server sessions. Other systems would be at significantly less risk:
- Workstations that are not shared between users would be at no risk, because the attacker would require the ability to log onto the system in order to place the Trojan horse.
- Servers would be at no risk, if standard best practices have been followed that advocate only allowing trusted users to log onto them.
- Remote Terminal server sessions would be at little risk, because each user's environment is isolated. That is, the system root is never the current folder - instead, the user's Documents and Settings folder is, but the permissions on this folder would not enable an attacker to place a Trojan horse there.

Mitigating factors:
- An attacker would require the ability to log onto the system interactively in order to place the Trojan horse program. It could not be placed remotely
- As discussed above, dedicated workstations, servers and remote terminal server sessions would be at less risk (or, in some cases, none at all) from the vulnerability.

Vulnerability identifier: CAN-2002-1184

This email is sent to NTBugtraq automatically as a service to my subscribers. Since its programmatically created, and since its been a long time since anyone paid actual money for my programming skills, it may or may not look that good...;-]

I can only hope that the information it does contain can be read well enough to serve its purpose.

Russ - Surgeon General of TruSecure Corporation/NTBugtraq Editor