Office (OOXML) / .XLSX malware analysis — malicious · 42e88d8e7f70d3a0

MALICIOUS

Office (OOXML) / .XLSX

1.16 MB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-04-08

MD5: eaff10223b07f4e5027b89d996d49073 SHA-1: 6386e8de6b5c505b6444914f517264c5a30fbf65 SHA-256: 42e88d8e7f70d3a005fe894ce668420607aae1882f30a16114a55d341419b709

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The file contains multiple Excel 4.0 macro sheets, indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. These macros are designed to execute arbitrary commands, which is a common technique for initial access or payload delivery. No specific family could be identified due to the generic nature of the macro sheets.

Heuristics 2

Excel 4.0 macro sheet (4 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. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
XLSB international XLM macro sheet hidden in .xlsx critical OOXML_XLSB_INTL_MACROSHEET_IN_XLSX

OOXML package is named .xlsx but contains XLSB workbook parts and an international Excel 4.0 macro sheet. This hides XLM macro execution from scanners that trust the extension or only inspect XML worksheet parts. The technique is macro execution, not a document-parser CVE.

Extracted artifacts 5

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`emf_00.emf` `36bcdb650f3335661fd30903e4ddbb92ac947513ed380f203fccc03424ff9fe4`	ooxml-emf	OOXML EMF part: xl/media/image1.emf	6145428 bytes
`xlm_sheet_00.bin` `44e1c910560c290cf1fe3eb0d0256a21f957a1765ea926de110b1985b1f72819`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin	1717 bytes
`xlm_sheet_01.bin` `ec25b05dca7aaeaed79bb62fb6411ee9f85904d5e8709aa43d05d83ea361677c`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/intlsheet2.bin	792 bytes
`xlm_sheet_02.bin` `f0a9425b8507f47d4bffbfc9986e6f77a1eec5a7b094745fec3307154c314949`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	402 bytes
`xlm_sheet_03.bin` `7b780847888f3179b9a2306b1d9dd4b22d991fb4b1641b18d3184a5b6ac9038f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet2.bin	322 bytes

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