From: dotslash at snosoft.com (KF)
Subject: HTML Help API - Privilege Escalation

I forgot to mention that another variation on this attack is to right 
click on the html help page and choose "view source". You will now have 
a notepad.exe running as SYSTEM. From there you can go to file then open 
and choose c:\windows\system32\cmd.exe and open that bad johnny. I have 
also seen instances where you can click the Options icon and then choose 
"Internet options" which give you the IE internet options screen. From 
there you can go to
"temporary internet files - settings" button. Clicking either "view 
objects" or "view files" will allow you to do the cmd.exe trick from 
above. If for some odd reason you can not navigate to cmd.exe you also 
have the option of changing NTFS permissions on key files so that you 
can trojan them or do something else along those lines.

If an application provides help as the SYSTEM user and uses either 
winhlp32.exe or hh.exe it can potentially be exploited by the variations 
both Brett and I have mentioned.

-KF

Brett Moore wrote:

>=====================================================================
>= HTML Help API - Privilege Escalation
>=
>= Tested against:
>=   HTML Help Control Version 5.2.3735.1
>=
>= brett.moore@...urity-assessment.com
>= http://www.security-assessment.com
>=
>= Originally posted: October 24th, 2003
>=====================================================================
>
>== Background ==
>
>Microsoft Windows allows applications to use a standard method of
>displaying and handling help files. One of these methods is using 
>the HTML help API.
>
>(From MSDN)
>- HTML Help API Overview
>- The HTML Help application programming interface (API) enables a 
>- Windows program to create a help window that displays a help topic.
>- The Windows program has complete control over the type, style, and
>- position of the help window. 
>-
>- The fundamental feature of the HTML Help API is the help window.
>- Through the API commands, you can create a help window that hosts 
>- a Microsoft Internet Explorer DLL (Shdocvw.dll) and displays an 
>- HTML file that you specify. 
>(End MSDN)
>
>The HTML help API consists of one function that an application uses
>to pass commands.
>
>	HWND HtmlHelp(
>              HWND    hwndCaller,
>              LPCSTR  pszFile,
>              UINT    uCommand,
>              DWORD   dwData) ;
>
>When an application loads a help file using this function it passes
>the name of the file through the pszFile parameter. It appears that
>this function does not drop any privileges before invoking the help
>viewer.
>
>If a SYSTEM level application uses this function to display a help file,
>the HTML help viewer will be running with SYSTEM rights.
>
>Part of the help window consists of an instance of Internet Explorer
>which allows a user to browse the local drive. 
>
>By selecting jump to URL from the window system menu, a user can enter
>a path name (c:\), right-mouse-click on a file and then select open
>with cmd.exe to be given a SYSTEM level command shell window.
>
>== Example Vulnerable Programs ==
>
>>From our testing, any application running at a higher security level
>that invokes htmlhelp without dropping privileges is vulnerable.
>We tested various Personal Firewall and Antivirus applications and 
>found some to be vulnerable to this attack.
>We found no 'default' windows applications vulnerable to this attack,
>but think that it is something that application developers need to be
>aware of.
>
>== Solutions ==
>
>The HTML help view (hh.exe) should be called externally passing the
>helpfile name as a parameter.
>
>Security rights could be dropped through the use of system() or 
>CreateProcess() functions. CreateProcessAsUser() or 
>ImpersonateLoggedOnUser() could be used to control the rights that
>htmlhelp executes with.
>
>If an interactive window requires SYSTEM rights, its functionality should
>be limited to those functions requiring the higher level of privilege.
>
>== Credit ==
>
>Brett Moore from security-assessment.com
>
>== 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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>
>  
>

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