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Title: Windows 2000 Default Permissions Could Allow Trojan Horse
Program (Q327522)
Date: 30 October 2002
Software: Windows 2000
Impact: Trojan Horse program execution
Max Risk: Moderate
Bulletin: MS02-064

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-064.asp.

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Issue:

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.

Risk Rating:

• Internet systems: Low
• Intranet systems: Low
• Client systems: Moderate

Patch Availability:

• This vulnerability requires an administrative procedure rather
  than a patch. The needed changes are discussed in the FAQ.
  Please read the Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms02-064.asp
  for information on obtaining this patch.

Acknowledgment:

• Jason Miller of Security Focus (http://www.securityfocus.com)

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