Office (OOXML) / .XLSX malware analysis — malicious · 99ca23cc10120110

MALICIOUS

Office (OOXML) / .XLSX

141.3 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000

MD5: c9b81f7ea7055322512273aa1501e5f4 SHA-1: 9302c3f4308ae78e802a0f036228824071655f33 SHA-256: 99ca23cc10120110da72373e96842543e8983b5fa125acf662c89ada32b3c7b7

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 the XLSX file. These macros are capable of executing arbitrary commands, which is a common technique for initial access or payload delivery. However, the macro content is heavily truncated and obfuscated, preventing a more detailed analysis of its specific actions or the reconstruction of any URLs or commands.

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` `56060824810b325ea5408c6d644d9a49ed3042163d98ffd7959e438b18b7a4f8`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	670170 bytes

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