Office (OOXML) / .XLSX malware analysis — malicious · 41a1285cb88e7c31

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 7d0f256871ff67213d676ed37d2a115a SHA-1: f961115e5d314023546d5eac32c9acd9fd627dcb SHA-256: 41a1285cb88e7c3191bbce029843ba0619dad4b905b33252ddc1c3106656a173

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. While the macro content is heavily truncated and obfuscated, the presence of this type of macro sheet is a strong indicator of malicious intent, often used to download and execute further stages. The primary function appears to be command execution via these macros.

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` `a6dc66d07ca90a677da2c366e6a0efc7fdc7901ae971a446a052a5b82b967b79`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	7303 bytes

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