It was Andrew (thanks!) who brought LdrRegisterDllNotification to my attention by asking on twitter if anyone has seen any malware using it. I couldn’t find any malware, but the function itself triggered my interest.

I quickly implemented a proof of concept. It shows how the callback that the API is registering could be utilized as a lame anti-* trick by malware that drops DLLs (in a case I am demoing), and maybe to do a few more tricky things (as I discuss below).

Consider the first .exe – let’s call it ‘good.exe’.

When executed, it drops a DLL called ‘foo.dll’.

It then resolves its one and only export ‘Bar’ and executes the function. The function shows a simple message box with a ‘Good’ message:

The second .exe is called ‘better.exe’ (obviously 🙂 ).

It drops the very same ‘foo.dll’.

Functionally, it is almost identical with ‘good.exe’ as it is using the same source code. The only difference is that it registers the callback using a LdrRegisterDllNotification function. From now on, anytime a DLL is loaded the callback function takes control and is free to modify the content of the loaded DLL ‘on the fly’. As such, it can easily patch it and create a complete different memory image from the one we may expect by just looking at a static file ‘dropped’ by the .exe.

In my case the change is of a ‘visualame’ type. It’s for us to observe it.

The callback does only one thing – it checks if the string at a hardcoded offset inside the loaded DLL is equal to ‘Good’ and swaps it with a new string ‘Evil’; therefore, running the ‘better.exe’ will produce the following result:

The example is intentionally simple, but there are many things that could be done here – the callback allows one to f.ex.

• disable unwanted DLLs (by f.ex. patching their code)
• detecting sandbox DLLs at a different stage (also use as a different enumeration method for loaded DLLs)
• swapping data and code of modules on the fly
• resolving API pointers earlier and potentially hooking / patching APIs used later in the code
• introducing simple, atomic, business logic changes to the executed code (hard to spot) f.ex. modify JNZ to JZ, NOPing some instructions, etc.
• etc.

Both files can be downloaded here.

Nothing ground breaking, but good to know about.

WMI is an important component of Windows OS and everyone knows about it so I won’t get into detail about what it is (read the linked wikipedia article if you want to know). I will focus on practical stuff instead which we come across more and more often.

I will begin by saying that nowadays lots of malware is using WMI – either to establish a stealthy persistence mechanism, or query various information from the system. This typically is done using WQL queries which are so popular that even a couple of typical OS commands are implemented as ‘processors’ simply interpreting results of many WQL queries instead of actually using old-school APIs.

A good example is a tasklist.exe. If you ever launched it from a command line and observed a slight delay before it returned the data it is because it has to ‘talk’ to WMI first and sometimes WMI initialization may take a while.

This particular program is actually a good example we can use to show what exactly happens when it ‘talks’ to WMI.

Have a look at the Tasklist.exe log below.

• First WMI connects to the WMI server – the ‘root\cimv2’ is a namespace used by most WMI classes
• Then it executes the WQL query

     SELECT 
        __PATH,
        ProcessId, 
        CSName, 
        Caption, 
        SessionId, 
        ThreadCount, 
        WorkingSetSize, 
        KernelModeTime, 
        UserModeTime  
     FROM 
        Win32_Process

• Then the result returned by the query is processed using the IWbemClassObject::Get method
• Finally, this obtained data is sent to the the console using a WriteConsoleW function

Apart from tasklist.exe, we can also find WQL in taskkill.exe.

Killing a process requires a different query, one that specifies f.ex. a name of the process:

     SELECT
        __PATH,
        ProcessId,
        CSName,
        Caption,
        SessionId,
        ThreadCount,
        WorkingSetSize,
        KernelModeTime,
        UserModeTime,
        ParentProcessId
     FROM
        Win32_Process
     WHERE
        (  Caption = "notepad.exe")

which is ran when we execute

taskkill.exe /im notepad.exe /f

The WMI is then queried for a method ‘Terminate’ which is supposed to kill the object. All of these queries are ran via COM so it’s a bit of a pain to analyze it, but once you get used to it it’s actually manageable (just a bit mundane).

Refer to a short Taskkill.exe log below.

As I mentioned above, malware often uses WQL queries and the most popular are listed below:

• select * from antispywareproduct
• select * from antivirusproduct
• select * from firewallproduct
• select * from win32_baseboard
• select * from win32_bios where manufacturer like ‘%xen%’ or (smbiosbiosversion like ‘%vbox%’) or (smbiosbiosversion like ‘%bochs%’) or (smbiosbiosversion like ‘%qemu%’) or (smbiosbiosversion like ‘%virtualbox%’)
• select * from win32_bios
• select * from win32_cdromdrive
• select * from win32_computersystem
• select * from win32_computersystemproduct
• select * from win32_diskdrive
• select * from win32_networkadapter where (name like ‘%tap%’) and (not pnpdeviceid like ‘%*isatap%’) and (netenabled = true)
• select * from win32_onboarddevice
• select * from win32_operatingsystem
• select * from win32_physicalmedia
• select * from win32_processor
• select * from win32_systemenclosure
• select * from win32_useraccount
• select * from win32_videocontroller
• select name, executablepath from win32_process

There are many more which often focus on sandbox detection, but I may cover them in a separate post.

Taskkill.exe log

IWbemLocator::ConnectServer: ‘root\cimv2’
IWbemServices::ExecQuery: (‘SELECT __PATH, ProcessId, CSName, Caption, SessionId, ThreadCount, WorkingSetSize, KernelModeTime, UserModeTime, ParentProcessId FROM Win32_Process WHERE (  Caption = “notepad.exe”)’)
IWbemServices::GetObjectA: Win32_Process
IWbemClassObject::GetMethod: Terminate

Tasklist.exe log

WbemLocator::ConnectServer): 'root\cimv2'
IWbemServices::ExecQuery ('SELECT __PATH, ProcessId, CSName, Caption, SessionId, ThreadCount, WorkingSetSize, KernelModeTime, UserModeTime  FROM Win32_Process')
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="0"
IWbemClassObject::Get: ProcessId=0
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=System Idle Process
IWbemClassObject::Get: ThreadCount=1
IWbemClassObject::Get: KernelModeTime=649121406250
IWbemClassObject::Get: UserModeTime=0
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=28672
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="4"
IWbemClassObject::Get: ProcessId=4
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=System
IWbemClassObject::Get: ThreadCount=48
IWbemClassObject::Get: KernelModeTime=103437500
IWbemClassObject::Get: UserModeTime=0
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=241664
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="412"
IWbemClassObject::Get: ProcessId=412
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=smss.exe
IWbemClassObject::Get: ThreadCount=3
IWbemClassObject::Get: KernelModeTime=156250
IWbemClassObject::Get: UserModeTime=156250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=442368
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="628"
IWbemClassObject::Get: ProcessId=628
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=csrss.exe
IWbemClassObject::Get: ThreadCount=11
IWbemClassObject::Get: KernelModeTime=12343750
IWbemClassObject::Get: UserModeTime=5312500
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=4444160
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="720"
IWbemClassObject::Get: ProcessId=720
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=winlogon.exe
IWbemClassObject::Get: ThreadCount=17
IWbemClassObject::Get: KernelModeTime=15156250
IWbemClassObject::Get: UserModeTime=2343750
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=5029888
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="764"
IWbemClassObject::Get: ProcessId=764
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=services.exe
IWbemClassObject::Get: ThreadCount=15
IWbemClassObject::Get: KernelModeTime=8927500000
IWbemClassObject::Get: UserModeTime=901250000
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=3727360
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="776"
IWbemClassObject::Get: ProcessId=776
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=lsass.exe
IWbemClassObject::Get: ThreadCount=20
IWbemClassObject::Get: KernelModeTime=143437500
IWbemClassObject::Get: UserModeTime=28906250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=1490944
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="932"
IWbemClassObject::Get: ProcessId=932
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=vmacthlp.exe
IWbemClassObject::Get: ThreadCount=1
IWbemClassObject::Get: KernelModeTime=0
IWbemClassObject::Get: UserModeTime=156250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=2768896
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="948"
IWbemClassObject::Get: ProcessId=948
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=svchost.exe
IWbemClassObject::Get: ThreadCount=17
IWbemClassObject::Get: KernelModeTime=781250
IWbemClassObject::Get: UserModeTime=468750
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=5214208
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1032"
IWbemClassObject::Get: ProcessId=1032
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=svchost.exe
IWbemClassObject::Get: ThreadCount=9
IWbemClassObject::Get: KernelModeTime=625000
IWbemClassObject::Get: UserModeTime=781250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=4546560
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1152"
IWbemClassObject::Get: ProcessId=1152
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=svchost.exe
IWbemClassObject::Get: ThreadCount=49
IWbemClassObject::Get: KernelModeTime=125937500
IWbemClassObject::Get: UserModeTime=50781250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=17682432
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1188"
IWbemClassObject::Get: ProcessId=1188
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=svchost.exe
IWbemClassObject::Get: ThreadCount=5
IWbemClassObject::Get: KernelModeTime=781250
IWbemClassObject::Get: UserModeTime=312500
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=3985408
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1224"
IWbemClassObject::Get: ProcessId=1224
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=svchost.exe
IWbemClassObject::Get: ThreadCount=4
IWbemClassObject::Get: KernelModeTime=0
IWbemClassObject::Get: UserModeTime=156250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=3346432
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1396"
IWbemClassObject::Get: ProcessId=1396
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=spoolsv.exe
IWbemClassObject::Get: ThreadCount=11
IWbemClassObject::Get: KernelModeTime=625000
IWbemClassObject::Get: UserModeTime=156250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=6545408
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1776"
IWbemClassObject::Get: ProcessId=1776
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=explorer.exe
IWbemClassObject::Get: ThreadCount=10
IWbemClassObject::Get: KernelModeTime=21718750
IWbemClassObject::Get: UserModeTime=6093750
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=19316736
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="2008"
IWbemClassObject::Get: ProcessId=2008
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=vmtoolsd.exe
IWbemClassObject::Get: ThreadCount=5
IWbemClassObject::Get: KernelModeTime=17031250
IWbemClassObject::Get: UserModeTime=8593750
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=12140544
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="2024"
IWbemClassObject::Get: ProcessId=2024
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=ctfmon.exe
IWbemClassObject::Get: ThreadCount=1
IWbemClassObject::Get: KernelModeTime=156250
IWbemClassObject::Get: UserModeTime=312500
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=3600384
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="476"
IWbemClassObject::Get: ProcessId=476
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=PERSFW.exe
IWbemClassObject::Get: ThreadCount=6
IWbemClassObject::Get: KernelModeTime=2187500
IWbemClassObject::Get: UserModeTime=1093750
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=6897664
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="516"
IWbemClassObject::Get: ProcessId=516
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=vmtoolsd.exe
IWbemClassObject::Get: ThreadCount=7
IWbemClassObject::Get: KernelModeTime=124531250
IWbemClassObject::Get: UserModeTime=63281250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=13619200
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1472"
IWbemClassObject::Get: ProcessId=1472
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=TPAutoConnSvc.exe
IWbemClassObject::Get: ThreadCount=5
IWbemClassObject::Get: KernelModeTime=1093750
IWbemClassObject::Get: UserModeTime=468750
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=4669440
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1796"
IWbemClassObject::Get: ProcessId=1796
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=TPAutoConnect.exe
IWbemClassObject::Get: ThreadCount=1
IWbemClassObject::Get: KernelModeTime=5312500
IWbemClassObject::Get: UserModeTime=2500000
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=5267456
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="2040"
IWbemClassObject::Get: ProcessId=2040
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=cmd.exe
IWbemClassObject::Get: ThreadCount=1
IWbemClassObject::Get: KernelModeTime=156250
IWbemClassObject::Get: UserModeTime=156250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=2961408
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="588"
IWbemClassObject::Get: ProcessId=588
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=wmiprvse.exe
IWbemClassObject::Get: ThreadCount=7
IWbemClassObject::Get: KernelModeTime=0
IWbemClassObject::Get: UserModeTime=156250
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=6332416
IWbemClassObject::Get: __PATH=\\<hostname>\root\cimv2:Win32_Process.Handle="1592"
IWbemClassObject::Get: ProcessId=1592
IWbemClassObject::Get: CSName=<hostname>
IWbemClassObject::Get: Caption=tasklist.exe
IWbemClassObject::Get: ThreadCount=4
IWbemClassObject::Get: KernelModeTime=2031250
IWbemClassObject::Get: UserModeTime=2187500
IWbemClassObject::Get: SessionId=0
IWbemClassObject::Get: WorkingSetSize=5816320