Malicious Office (OOXML) / .XLSX — malware analysis report

Heuristics 6

• Excel 4.0 macro sheet (31 sheet(s)) critical OOXML_XLM_MACROSHEET
  Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks.
• Excel 4.0 Auto_Open defined name critical OOXML_XLM_AUTOOPEN_DEFINEDNAME
  Workbook defines _xlnm.Auto_Open or _xlnm.Auto_Close while containing an XLM macro sheet. This is the OOXML/XLSB auto-execution shape for Excel 4.0 macros.
• Dangerous XLM formula APIs: RUN, CALL, HALT critical OOXML_XLM_DANGEROUS_FN
  Excel 4.0 macro sheet uses formula APIs that call directly into Win32 (=CALL/=EXEC/=REGISTER/=FORMULA). These are the primitives used to download payloads, write files, and start processes from an XLM macro without invoking VBA.
• Suspicious extracted artifact medium 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.
• Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
  Excel workbook contains 31 hidden sheet(s) — hidden sheets are commonly used to conceal macro code, staging data, or intermediate payload construction
• Embedded URL info EMBEDDED_URL
  One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
  URL http://giuden.com/purge.exe

  • http://schemas.openxmlformats.org/spreadsheetml/2006/main
  • http://schemas.microsoft.com/office/excel/2006/main
  • http://schemas.openxmlformats.org/officeDocument/2006/relationships
  • http://schemas.openxmlformats.org/markup-compatibility/2006
  • http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac
  • http://schemas.microsoft.com/office/spreadsheetml/2014/revision
  • http://schemas.microsoft.com/office/spreadsheetml/2015/revision2
  • http://schemas.microsoft.com/office/spreadsheetml/2016/revision3
  • http://schemas.microsoft.com/office/spreadsheetml/2016/revision6

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