Malicious Office (OOXML) — malware analysis report

Heuristics 4

• Excel 4.0 macro sheet (1 sheet(s)) critical 3 related findings 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 macro sheet stored under disguised package path critical OOXML_XLM_DISGUISED_RELATIONSHIP
  OOXML package declares an xlMacrosheet relationship whose target is outside the canonical xl/macrosheets/ path. Excel follows the relationship type, while path-only scanners can miss the macro execution surface.
• 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.
• Binary XLM macro sheet with WinAPI/download strings critical OOXML_XLM_BINARY_WINAPI_STRINGS
  Excel 4.0 macro sheet is stored as BIFF12/XLSB binary data and contains Win32 download or process-execution API strings such as URLDownloadToFileA, ShellExecuteA, or CreateDirectoryA. These strings are high-signal in XLM macro sheets and catch payload-download macros that XML-formula scanners cannot parse.

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