Office (OOXML) / .XLSX malware analysis — malicious · 4da267b4ad63b844

MALICIOUS

Office (OOXML) / .XLSX

114.5 KB Created: 2021-02-03 15:28:44 UTC Authoring application: Microsoft Excel 16.0300

MD5: c1c29257a0f8db7d04c6d4ca9f436584 SHA-1: 79eb82f14303ee8bb2035b685fa20085fac8d065 SHA-256: 4da267b4ad63b844ed0916af8a1abfa4b1f92c055417408430fc84ff8a4e0abf

120 Risk Score

Malware Insights

MITRE ATT&CK

T1566.002 Spearphishing Attachment T1059.005 Visual Basic

The file is identified as a malicious Excel 4.0 macro sheet, disguised within the OOXML package. The heuristics indicate the presence of an Excel 4.0 macro sheet stored under a disguised package path, suggesting an attempt to evade detection. The macro sheet itself is heavily truncated, preventing a detailed analysis of its specific actions, but the presence of disguised macros strongly implies a malicious intent, likely for initial execution or payload delivery.

Heuristics 2

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.
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.

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `3fd2c5ac9f1339b006d4b8558a66e92632e93690860205c61803635b864cb6a6`	xlm-macrosheet	OOXML XLM macro sheet: xl/xls/sheet1.bin	1007414 bytes

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