Office (OOXML) / .XLSX malware analysis — malicious · 90dd46cc4ee0a5ae

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 3d4b4960fe90b061ef20f8e38b6da964 SHA-1: 44b007e572100d78059edde0c5450c83927a1bd4 SHA-256: 90dd46cc4ee0a5aeef3d04a887e233b29657b9ca8ff6aa8e48bcaff475d08b14

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. Analysis of the macro sheet reveals a path string that reconstructs to 'C:\ProgramData\excel.rtf'. This suggests the macro's purpose is to execute commands, potentially to download and run a malicious second-stage payload from this location or to use it as a staging area.

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` `d41115b52ecc85ddecc65560f68907ccd5b9456045ea7b21cefd3ed9d39b1c77`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	97680 bytes

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