Office (OOXML) / .XLSX malware analysis — malicious · 38e36a6b7bf101f5

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 1479f6bfc2c47932d8eee6cf4db5c7f4 SHA-1: 7594bd2fb1fa9005662ece3c490fe80d28463e2c SHA-256: 38e36a6b7bf101f5a8ddfb13756b8975413c91bad1828f83258afa6e564f1c32

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The file is an Excel spreadsheet containing Excel 4.0 macros, as indicated by the OOXML_XLM_MACROSHEET heuristic. The macro sheet appears to be constructing a path to execute a file named 'update.exe' from the 'ProgramData\Microsoft\Windows\Start Menu\Programs\Startup' directory. This strongly suggests the macro's purpose is to establish persistence and execute a downloaded payload.

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` `f85518d086ec3511e71a5b23d311fd384aec7e17e900c77b76b3b8a739356ae1`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	8013 bytes

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