Office (OOXML) / .XLSX malware analysis — malicious · bb50b1df501e549a

MALICIOUS

Office (OOXML) / .XLSX

82.2 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000

MD5: 38115c1f425bfe9ed9a30195503a6e30 SHA-1: 1fd11b214a3f33a63a7ed8b1558af7e312d4749f SHA-256: bb50b1df501e549ac68b2ec34573c7883d17e947ec5e1ab28938243c108a2fa4

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The critical heuristic firing indicates the presence of Excel 4.0 macros within an XLSX file. The macro sheet contains obfuscated strings that, when partially reconstructed, suggest a path to 'C:\ProgramData\excel.rtf'. This indicates the macro's intent is likely to download and execute a second-stage payload from this location, a common technique for initial access.

Heuristics 1

Excel 4.0 macro sheet (1 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.

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `5403b8fa3ebe8c9737f1bbab5775409c830f688cee00a4365c8958f8fdf20ef1`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	266112 bytes

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