Thursday, October 30, 2014

BlackEnergy 2 (alias BlackEnergy Version 2) Live Debugging

Last night I took a quick look at BlackEnergy 2, a rootkit that surfaced in 2010. BlackEnergy 2 was essentially a rewrite of its predecessor as BlackEnergy 2 contains rootkit techniques, process-injection, and encryption. Surprisingly for being a now 'dated' rootkit, there's really not too much accessible (or not buried) reverse kernel-debugging documentation for the rootkit aside from when it was first surfacing. A lot of misc. information pops up throughout very few blogs/forums that are Russian, but that's about it.

There's a lot of additional lore behind the rootkit, but I really won't go into that. If you're interested about where the rootkit core came from before it was implemented into BlackEnergy 2, BlackReleaver is the answer!

NT Corruption

First off, we can view corruption regarding ntokskrnl:


 lkd> !chkimg -d -v nt  
 Searching for module with expression: nt  
 Will apply relocation fixups to file used for comparison  
 Will ignore NOP/LOCK errors  
 Will ignore patched instructions  
 Image specific ignores will be applied  
 Comparison image path: C:\Symbols\ntoskrnl.exe\41108004214780\ntoskrnl.exe  
 No range specified  

 Scanning section:  .text  
 Size: 466369  
 Range to scan: 804d7580-80549341  
   804ded5a-804ded5d 4 bytes - nt!KiBBTUnexpectedRange+8
      [ 00 ff 09 00:6b a0 c1 01 ]  
   804e59a1-804e59a5 5 bytes - nt!KeInsertQueueApc (+0x6c47)  // Not malicious -- Malwarebytes.
      [ 8b ff 55 8b ec:e9 e4 45 4e 77 ]  
 Total bytes compared: 466369(100%)  
 Number of errors: 9  

!chkimg compares the current loaded executable with the version within the symbol store. This is a helpful command to detect corruptions with images, and especially helpful when dealing with rootkits. The -d parameter displays a summary of all mismatched areas. The -v parameter makes the information verbose. In this case, the -v parameter is optional.

As noted above, we have two out-of-range values. We're interested in disassembling nt!KiBBTUnexpectedRange+8, but not nt!KeInsertQueueApc (+0x6c47). nt!KeInsertQueueApc (+0x6c47) as I commented above is in relation to the Chameleon technology from Malwarebytes. I had MWB ARK installed on this VM for testing purposes, so that is where it was spawning from.

nt!KiBBTUnexpectedRange+8 Disassembly - Healthy

If we disassemble nt!KiBBTUnexpectedRange+8 on a system not infected with BlackEnergy 2, we should expect similar results:

 lkd> u nt!KiBBTUnexpectedRange+8  
 nt!KiBBTUnexpectedRange+0x8:  
 804ded5a 00ff      add   bh,bh  
 804ded5c 0900      or   dword ptr [eax],eax  
 804ded5e 0bc0      or   eax,eax  
 804ded60 58       pop   eax  
 804ded61 5a       pop   edx  
 804ded62 8bec      mov   ebp,esp  
 804ded64 89ae34010000  mov   dword ptr [esi+134h],ebp  
 804ded6a 0f8490020000  je   nt!KiFastCallEntry+0x8d (804df000)  

nt!KiBBTUnexpectedRange+8 Disassembly - Corrupted

If we disassemble nt!KiBBTUnexpectedRange+8 on a system that has been infected with BlackEnergy 2, we should expect similar results:

 lkd> u nt!KiBBTUnexpectedRange+8  
 nt!KiBBTUnexpectedRange+0x8:  
 804ded5a 6ba0c1010bc058 imul  esp,dword ptr [eax-3FF4FE3Fh],58h  
 804ded61 5a       pop   edx  
 804ded62 8bec      mov   ebp,esp  
 804ded64 89ae34010000  mov   dword ptr [esi+134h],ebp  
 804ded6a 0f8490020000  je   nt!KiFastCallEntry+0x8d (804df000)  
 804ded70 8d15509b5580  lea   edx,[nt!KeServiceDescriptorTableShadow+0x10 (80559b50)]  
 804ded76 8b4a08     mov   ecx,dword ptr [edx+8]  
 804ded79 8b12      mov   edx,dword ptr [edx]  

So, why do we have corruptions in ntoskrnl and a corrupted nt!KiBBTUnexpectedRange+8 output? It's a side effect of the rootkit creating additional 'fake' service tables. It does this by patching the ETHREAD SystemTable pointer, which allows for things such as user threads to be patched, thread creation notification and service table pointer updating by using PsSetCreateThreadNotifyRoutine, etc.

The main use behind creating fake service tables is it gives anti-rootkit software a much harder time (harder back in 2010, at least) detecting its presence. It doesn't just 'hook' and/or modify the SSDT (which as we know would be a big red flag), it instead creates its own fake service tables, and then hooks (acquires?) the following functions:

 NtDeleteValueKey  
 NtEnumerateValueKey  
 NtEnumerateKey  
 NtOpenKey  
 NtOpenProcess  
 NtOpenThread  
 NtProtectVirtualMemory  
 NtQuerySystemInformation  
 NtReadVirtualMemory  
 NtSetContextThread  
 NtSetValueKey  
 NtSuspendThread  
 NtTerminateThread  
 NtWriteVirtualMemory
 etc...  

KTHREAD Structure
 
Given we're adding new/fake service tables, we need applications to be able to access them. This is done by using pointers as discussed above, which is accomplished in the KTHREAD Structure. Every single thread has a pointer to a ServiceTable which is ultimately set by KeInitThread. Additionally, if the thread requires GUI functions within the Shadow SSDT, PsConvertToGuiThread is called.

We can dump the KTHREAD Structure:

 lkd> dt -v nt!_KTHREAD  
 struct _KTHREAD, 73 elements, 0x1c0 bytes  
   +0x000 Header      : struct _DISPATCHER_HEADER, 6 elements, 0x10 bytes  
   +0x010 MutantListHead  : struct _LIST_ENTRY, 2 elements, 0x8 bytes  
   +0x018 InitialStack   : Ptr32 to Void  
   +0x01c StackLimit    : Ptr32 to Void  
   +0x020 Teb       : Ptr32 to Void  
   +0x0e0 ServiceTable   : Ptr32 to Void  

At this point if you'd like to see the tables, you can use the following command:

 !for_each_thread ".echo Thread: @#Thread; dt nt!_kthread ServiceTable @#Thread"   

If you see anything other than KeServiceDescriptorTable or KeServiceDescriptorTableShadow, it's a new/fake ServiceTable.

Registry Hiding

In order to survive reboots, etc, it hides its registry entry. If you're using Windows' Registry Editor, it won't find the hidden entry. For example, here's our hidden service:

 lkd> !ms_services  
 [205] | 0x01 | | qtcst | qtcst | SERVICE_RUNNING | \Driver\qtcst  

If we try and find qtcst with Registry Editor:


If we however use a 3rd party registry tool (any will probably work so long as it doesn't use Windows API calls):


We catch our culprit and the dropped driver red-handed. The driver renames after each reboot, so if you remove it and don't get the driver+registry entry at once, it'll just re-create with a different name.

Main.dll

 .exe SYS TMP cmd.exe /C b k e r n e l p l g _ d a t a getp v e r s i o n n a m e s l e e p f r e q c m d s p l u g i n s x%s_%X C:\ a d d r t y p e s e r v e r s i c m p _ a d d r b u i l d _ 
 i d str.sys \drivers\ \ \ . \ \ \ . \ G l o b a l \ %s%s { 9 D D 6 A F A 1 - 8 6 4 6 - 4 7 2 0 - 8 3 6 B - E D C B 1 0 8 5 8 6 4 A } main.dll .bdata {3D5A1694-CC2C-4ee7-A3D5-A879A9E3A623} 
 POST %.2X & = bid nt %d cn ln id ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ Content-Type: application/x-www-form-urlencoded _TEST_ .dll user32.dll advapi32.dll 
 wininet.dll ws2_32.dll DispatchCommand DispatchEvent GetLastError GetCurrentProcessId ExitThread CloseHandle KERNEL32.dll wsprintfA USER32.dll CoCreateInstance CoInitializeEx ole32.dll 
 OLEAUT32.dll WS2_32.dll RtlUnwind InterlockedExchange VirtualQuery main.dll ConfAllocGetTextByNameA ConfAllocGetTextByNameW ConfGetListNodeByName ConfGetNodeByName ConfGetNodeTextA 
 ConfGetNodeTextW ConfGetPlgNode ConfGetRootNode DownloadFile PlgSendEvent RkLoadKernelImage RkProtectObject SrvAddRequestBinaryData SrvAddRequestStringData  

Main.dll is the payload that is injected via trusted svchost. It contains as you can see a lot of readable stings, like str.sys for example. We can see str.sys in action here:


Overall, this rootkit was certainly a step up from most SSDT hooking/modification rootkits at the time. It can be a pain in the ass to remove if you don't kill everything properly : )

Thanks for reading.

References

Black Energy 2.1+
BlackEnergy Version 2 Analysis

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