Office (OOXML) / .XLSX malware analysis — malicious · 913375d9ef621f68

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 0c37045008234ac4d85a6df2b3a53650 SHA-1: fd51b31990bc89a116483e2a2d04cf53d16aea5e SHA-256: 913375d9ef621f68ab2937c539180fdc5baddb02fd3de7617bca2fe35aedcd36

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an Excel file containing Excel 4.0 macros, indicated by the OOXML_XLM_MACROSHEET heuristic. The embedded macro sheet appears to be constructing a path to an executable file, likely for execution. The macro attempts to write to 'C:\ProgramData\Microsoft\Excel\rtfB.exe', suggesting a downloader or dropper functionality.

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` `69e2df8f6beed7fa7c8e1926d8cbe6f81bf17ef11b2846cc0f9567ad64c3fbbb`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	112654 bytes

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