Raspberry Robin and its new anti-emulation trick – Cyber Security News Aggregator

Reported for the first time by Red Canary in 2021, Raspberry Robin was the 9th most prevalent threat in 2023 according to their “2024 Threat Detection Report”. Starting as a worm, it evolved to become an initial access broker for other threat actors. The success of Raspberry Robin comes from its constantly evolving evasion capabitilies, making it difficult to analyze and detect.

Despite Raspberry Robin being regularly analyzed by various vendors such as Check Point and Avast, our team discovered a recent variant featuring interesting and as-of-yet unknown anti-emulation techniques.

Windows Defender Emulator

During the Black Hat edition of 2018, Alexei Bulazel presented his work on the “Windows Defender Emulator” in a talk titled “Windows Offender: Reverse Engineering Windows Defender’s Antivirus Emulator”.

This talk was an extensive analysis of the Windows Defender emulator internals. A slide seems to have caught the threat actors’ and Red Teamers’ attention:

Presentation by Alexei Bulazel of artefacts in the Windows Defender Emulator

In the wild exploitation history

The first mention of a malware checking the then-published Defender emulator artifact is Arkei Stealer, reported in 2018 by Siber Vatan

Analysis of Arkei stealer Windows Defender Emulator bypass showing the use of GetComputerNameA and GetUserNameA functions and comparing the output with the emulator artefacts JohnDoe and HAL9TH — Analysis of Arkei stealer Windows Defender Emulator bypass

The anti-emulation technique spotted in Arkei was a string comparaison between:

The computer name and “HAL9TH”
The username and “JohnDoe”

Indeed, in the “Windows Defender Emulator”, the Windows API function GetComputerName always returns HAL9TH and GetUsername the string JohnDoe.

Between 2018 and 2022, this technique seemed restricted to stealers and was observed in Oski, Mars, StealC, Vidar, LOBSHOT and Qbot. In the latter, Trellix researchers found in 2022 that Qbot was using a new way to detect the Windows Defender emulator.

Trellix analysis of Qbot showing the use of a new anti-emulation technique

Instead of checking the current computer and username, Qbot looked for the existence of an emulator-specific file, C:INTERNAL__empty. If at first glance this check seemed original, this artefact was also disclosed in Bulazel’s talk.

Slide showing "C:INTERNAL__empty" in the listed files available in the Window Defender Emulator — Slide showing “C:INTERNAL__empty” in the listed files available in the Window Defender Emulator

The Raspberry Robin innovation

During an incident detected at one of our clients’, we came across a Raspberry Robin distributor acting as a crack/keygen website.

Screenshot of a Raspberry Robin distributor website

Instead of the advertised piracy software, the website provides zip files containing SFX (self-extracting) archives. The website offers the same file no matter what “crack/keygen” software the user chooses.

Once one of them is executed, 3 malware samples are dropped: two stealers (Pony and AZORULT) and Raspberry Robin. The latter is dropped as a .cpl file named keygen-step-2.cpl.

Execution flow of fake cracks distributed on keygenguru[.]com — Execution flow of fake cracks distributed on “keygenguru[.]com”

When executed, the program runs multiple anti-emulation/sandbox checks. However, one of the checks caught our attention:

Import of a non-existing function in kernel32

The malware tries to dynamically import the function MpVmp32Entry from Kernel32.dll and if the import succeeds, then the malware exits. However, this function doesn’t normally exist in Kernel32.

Bulazel’s presentation introduced the concept of VDLL. VDLLs are modified Windows system DLLs available only in the emulator, and such DLLs may export functions that don’t otherwise exist (shown in yellow below):

Presentation by Alexei Bulazelof of VDLL functions

The function MpVmp32Entry starts with Mp, which indicated that it could be one of the functions available only in the VDLL version of Kernel32.dll. We extracted the Kernel32 VDLL from the emulator in order to analyze its exports and found out that this function is indeed exported by the VDLL:

MpVmp32Entry function available in the Kernel32 VDLL — “MpVmp32Entry” function available in the Kernel32 VDLL

Later on, we analyzed a new sample from the same website and discovered that the VDLL function check performed by the malware was different. This time the imported VDLL function used for anti-emulation was MpReportEventEx. However, unlike MpVmp32Entry, the function MpReportEventEx is listed in Bulazel’s presentation.

Raspberry Robin seems to be the first malware to use VDLL specific function import as an anti-emulation trick and could exploit more advanced anti-Defender emulator trick in the future.

In order, to evade IOC-based detection, the Raspberry Robin sample distributed by this website is changed (probably re-packed) every 30 minutes (at the minutes 15 and 45 of every hour). This likely means that a Raspberry Robin sample distributed on this website exists only for 30 minutes. This short lifespan leads to an absence of results when reseaching information based on the file hash making the hunt a little bit harder for the researcher.

Potential Windows Defender emulator artifacts used for anti-emulation

Files and directories

aaa_TouchMeNot_
_TouchMeNot_
__empty
C:myapp.exe
C:Mirc
C:Mircmirc.ini
C:Mircscript.ini

Strings

HAL9TH
JohnDoe
MpSockVendor
MPGoodStatus
MpDisableSehLimit

VDLL exports

NtControlChannel
ObjMgr_ValidateVFSHandle
ThrdMgr_GetCurrentThreadHandle
ThrdMgr_SaveTEB
ThrdMgr_SwitchThreads
VFS_CopyFile
VFS_DeleteFile
VFS_DeleteFileByHandle
VFS_FileExists
VFS_FindClose
VFS_FindFirstFile
VFS_FindNextFile
VFS_FlushViewOfFile
VFS_GetAttrib
VFS_GetHandle
VFS_GetLength
VFS_MapViewOfFile
VFS_MoveFile
VFS_Open
VFS_Read
VFS_SetAttrib
VFS_SetCurrentDir
VFS_SetLength
VFS_UnmapViewOfFile
VFS_Write
MpAddToScanQueue
MpCreateMemoryAliasing
MpCallPostEntryPointCode
MpCallPreEntryPointCode
MpDispatchException
MpExitThread
MpFinalize
MpGetCurrentThreadHandle
MpGetCurrentThreadId
MpGetLastSwitchResult
MpGetPseudoThreadHandle
MpGetSelectorBase
MpGetVStoreFileHandle
MpHandlerCodePost
MpIntHandler
MpIntHandlerParam
MpIntHandlerReturnAddress
MpNtdllDatatSection
MpReportEvent
MpReportEventEx
MpReportEventW
MpSehHandler
MpSetSelectorBase
MpStartProcess
MpSwitchToNextThread
MpSwitchToNextThread_WithCheck
MpSwitchToNextThread_NewObjManager
MpTimerEvent
MpTimerEventData
MpUfsMetadataOp
MpValidateVFSHandle
MpVmp32Entry
MpVmp32FastEnter

Indicators of compromise (IOCs)

Associated IOCs are also available on our GitHub repository.

Hashes (SHA-256)

242851abe09cc5075d2ffdb8e5eba2f7dcf22712625ec02744eecb52acd6b1bf|keygen-step-2.cpl (Raspberry Robin)
483adf61d7d932003659d5d6242eace29ea8416ec810749333793e0efa91610d|keygen-step-2.cpl (Raspberry Robin)
50158e22481acabc56d8e3d318d6d709fcb7a9e442e76157b518d19e13f8e520|keygen-step-2.cpl (Raspberry Robin)
93672d67e8100bb984f866888cb042727567d302b30b91356a2b2bc8cd3f7912|keygen-step-2.cpl (Raspberry Robin)
b5637231e25aa7da8fe925f5b97a2ccbfd082a5463b2a05d2b3221adb35e43d9|keygen-step-2.cpl (Raspberry Robin)
b81e857427411577552d1ecdd444efaeab23ec903192812d40ab3dd69df98ec5|keygen-step-2.cpl (Raspberry Robin)
c8d37df88009122c890cb95dc79d895d39339fe1efdcfa5e033d0aea171ffc3d|keygen-step-2.cpl (Raspberry Robin)
10b4b7e9469366bfe459c3cd674aeab0692cfd9272fe369ef56d2811623e4866|keygen-step-2.cpl (Raspberry Robin)

Hostnames

keygenguru[.]com|Raspberry Robin distribution platform

PE information

hrtbddd69.dll|DLL name in keygen-step-2.cpl export table
OsTlhtlohe|Exported function in keygen-step-2.cpl

Yara rules

rule anti_emulation_defender
{
    meta:
        description = "Research Windows Defender Emulator artefacts that can be used as anti-emulator by malware"
        references = "https://harfanglab.io/en/insidethelab/raspberry-robin-and-its-new-anti-emulation-trick/‎"
        hash = "242851abe09cc5075d2ffdb8e5eba2f7dcf22712625ec02744eecb52acd6b1bf"
        date = "2024-04-03"
        author = "Harfanglab"
        context = "file"

    strings:

        $s_00 = "aaa_TouchMeNot_" wide ascii nocase
        $s_01 = "_TouchMeNot_" wide ascii nocase
        $s_03 = "C:myapp.exe" wide ascii nocase
        $s_04 = "C:Mirc" wide ascii nocase
        $s_05 = "C:Mircmirc.ini" wide ascii nocase
        $s_06 = "C:Mircscript.ini" wide ascii nocase
        $s_07 = "HAL9TH" wide ascii nocase fullword
        $s_09 = "MpSockVendor" wide ascii nocase fullword
        $s_10 = "MPGoodStatus" wide ascii nocase fullword
        $s_11 = "MpDisableSehLimit" wide ascii nocase fullword
        $s_12 = "NtControlChannel" wide ascii nocase fullword
        $s_13 = "ObjMgr_ValidateVFSHandle" wide ascii nocase fullword
        $s_14 = "ThrdMgr_GetCurrentThreadHandle" wide ascii nocase fullword
        $s_15 = "ThrdMgr_SaveTEB" wide ascii nocase fullword
        $s_16 = "ThrdMgr_SwitchThreads" wide ascii nocase fullword
        $s_17 = "VFS_DeleteFileByHandle" wide ascii nocase fullword
        $s_18 = "VFS_DeleteFile" wide ascii nocase fullword
        $s_19 = "VFS_DeleteFileByHandle" wide ascii nocase fullword
        $s_20 = "VFS_FileExists" wide ascii nocase fullword
        $s_21 = "VFS_FindClose" wide ascii nocase fullword
        $s_22 = "VFS_FindFirstFile" wide ascii nocase fullword
        $s_23 = "VFS_FindNextFile" wide ascii nocase fullword
        $s_24 = "VFS_FlushViewOfFile" wide ascii nocase fullword
        $s_25 = "VFS_GetAttrib" wide ascii nocase fullword
        $s_26 = "VFS_GetHandle" wide ascii nocase fullword
        $s_27 = "VFS_GetLength" wide ascii nocase fullword
        $s_28 = "VFS_MapViewOfFile" wide ascii nocase fullword
        $s_29 = "VFS_MoveFile" wide ascii nocase fullword
        $s_30 = "VFS_Open" wide ascii nocase fullword
        $s_31 = "VFS_Read" wide ascii nocase fullword
        $s_32 = "VFS_SetAttrib" wide ascii nocase fullword
        $s_33 = "VFS_SetCurrentDir" wide ascii nocase fullword
        $s_34 = "VFS_SetLength" wide ascii nocase fullword
        $s_35 = "VFS_UnmapViewOfFile" wide ascii nocase fullword
        $s_37 = "MpAddToScanQueue" wide ascii nocase fullword
        $s_38 = "MpCreateMemoryAliasing" wide ascii nocase fullword
        $s_39 = "MpCallPostEntryPointCode" wide ascii nocase fullword
        $s_40 = "MpCallPreEntryPointCode" wide ascii nocase fullword
        $s_41 = "MpDispatchException" wide ascii nocase fullword
        $s_42 = "MpExitThread" wide ascii nocase fullword
        $s_43 = "MpFinalize" wide ascii nocase fullword
        $s_44 = "MpGetCurrentThreadHandle" wide ascii nocase fullword
        $s_45 = "MpGetCurrentThreadId" wide ascii nocase fullword
        $s_46 = "MpGetLastSwitchResult" wide ascii nocase fullword
        $s_47 = "MpGetPseudoThreadHandle" wide ascii nocase fullword
        $s_48 = "MpGetSelectorBase" wide ascii nocase fullword
        $s_49 = "MpGetVStoreFileHandle" wide ascii nocase fullword
        $s_50 = "MpHandlerCodePost" wide ascii nocase fullword
        $s_51 = "MpIntHandler" wide ascii nocase fullword
        $s_52 = "MpIntHandlerParam" wide ascii nocase fullword
        $s_53 = "MpIntHandlerReturnAddress" wide ascii nocase fullword
        $s_54 = "MpNtdllDatatSection" wide ascii nocase fullword
        $s_55 = "MpReportEvent" wide ascii nocase fullword
        $s_56 = "MpReportEventEx" wide ascii nocase fullword
        $s_57 = "MpReportEventW" wide ascii nocase fullword
        $s_58 = "MpSehHandler" wide ascii nocase fullword
        $s_59 = "MpSetSelectorBase" wide ascii nocase fullword
        $s_60 = "MpStartProcess" wide ascii nocase fullword
        $s_61 = "MpSwitchToNextThread" wide ascii nocase fullword
        $s_62 = "MpSwitchToNextThread_WithCheck" wide ascii nocase fullword
        $s_63 = "MpSwitchToNextThread_NewObjManager" wide ascii nocase fullword
        $s_64 = "MpTimerEvent" wide ascii nocase fullword
        $s_65 = "MpTimerEventData" wide ascii nocase fullword
        $s_66 = "MpUfsMetadataOp" wide ascii nocase fullword
        $s_67 = "MpValidateVFSHandle" wide ascii nocase fullword
        $s_68 = "MpVmp32Entry" wide ascii nocase fullword
        $s_69 = "MpVmp32FastEnter" wide ascii nocase fullword

        $filter_00 = "mpengine.pdb" ascii nocase
        $filter_01 = "MsMpEngCP.pdb" ascii nocase
        $filter_02 = "MsMpEngSvc.pdb" ascii nocase
        $filter_03 = "MpGear.pdb" ascii nocase
        $filter_04 = "mrtstub.pdb" ascii nocase
        $filter_05 = "mrt.pdb" ascii nocase
        $filter_06 = "ntoskrnl.pdb" ascii nocase
        $filter_07 = "mscorlib.pdb" ascii nocase
        $filter_08 = "dbghelp.pdb" ascii nocase
        $filter_09 = "msvcrt.pdb" ascii nocase
        $filter_10 = "mrt.exe" wide ascii nocase
        $filter_11 = "PEBMPAT:Obfuscator_EW2" wide ascii
        $filter_12 = "Unimplemented type change to VT_" wide ascii
        $filter_13 = "Initialize engine first!" wide ascii
        $filter_14 = "VirTool:Win32/Obfuscator" wide ascii
        $filter_15 = "VDMConsoleOperation" wide ascii
        $filter_16 = "VDMOperationStarted" wide ascii
        $filter_17 = "sigutilsvdlls" ascii
        $filter_18 = "Microsoft.Windows.MalwareRemovalTool" wide ascii
        $filter_19 = "AppVISVSubsystems32.pdb" ascii nocase
        $filter_20 = "Microsoft.AppV.ClientProgrammability.Eventing.pdb" ascii nocase
        $filter_21 = "AppVISVSubsystems64.pdb" ascii nocase
        $filter_22 = "AppVEntSubsystems.pdb" ascii nocase
        $filter_24 = "shell32.pdb" ascii nocase
        $filter_25 = "version.pdb" ascii nocase
        $filter_26 = "mscoree.pdb" ascii nocase
        $filter_27 = "ws2_32.pdb" ascii nocase
        $filter_28 = "advapi32.pdb" ascii nocase
        $filter_29 = "AppVEntSubsystems64.pdb" ascii nocase
        $filter_30 = "AppVEntSubsystems32.pdb" ascii nocase
        $filter_31 = "AppVISVSubsystems.pdb" ascii nocase
        $filter_32 = "mpengine.dll" ascii wide nocase
        $filter_33 = "VFSAPI_VFS_" ascii wide

    condition:
        uint16(0) == 0x5A4D
        and uint32(uint32(0x3C)) == 0x00004550
        and filesize < 5MB
        and 1 of ($s_*)
        and not 1 of ($filter*)
}

Published on 3 April, 2024

Last update on 5 April, 2024

Source: https://harfanglab.io/en/insidethelab/raspberry-robin-and-its-new-anti-emulation-trick/

Tags: WORM, INITIAL ACCESS, EXPLOIT, WINDOWS, HUNT