Office (OOXML) / .XLSX malware analysis — malicious · f99d44c28ed1a1d9

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 81574ec946727e2b1f6a27344fb331ae SHA-1: 291a97ebcbeb95bdf975e2e8c6de9a5f4ce99d51 SHA-256: f99d44c28ed1a1d98c19541455a621e96dbf5fd52395774e7e8d53e2bdd5ed9d

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an Excel 4.0 macro sheet, indicated by the OOXML_XLM_MACROSHEET heuristic. Excel 4.0 macros are capable of executing arbitrary commands, which is a common technique for initial access or payload delivery. The extracted macro content is heavily obfuscated and truncated, preventing a detailed analysis of its specific actions or reconstructed IOCs. However, the presence of the macro sheet itself is a strong indicator of malicious intent.

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` `5995e463c3fa841f92051906b8af40bd349cb424634ff09cb8a6d3c42364c52f`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	6995 bytes

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