Office (OOXML) / .XLSX malware analysis — malicious · f4e3013be0615f60

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 75c325deec0cae07e089f47028c4e444 SHA-1: ff3d0672ff1a95212063a42779538c1896d3b77c SHA-256: f4e3013be0615f60a3a6f6d3d3b26aa5239fe270e404dd465e1b99c2b594b4f8

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 extracted macro code appears to be attempting to write an executable file named 'a.exe' to the startup directory 'C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup\'. This suggests the macro is intended to download and execute a second-stage payload, establishing persistence.

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` `9529d1e9af73fae4c6925d16fcb49f7ee67b4f7120d8b3af26818ff65a01740a`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	7807 bytes

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