Office (OOXML) / .XLSX malware analysis — malicious · 36429f3cfbb87f9e

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: fcbda29e76d3ff677ec01b0d6c363433 SHA-1: 31e3cc8aeacb6a3ff5f96bac363653320fc90804 SHA-256: 36429f3cfbb87f9efbcf4e0939253c1c418568eb310e13ed6aab7e0e4912426c

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The primary finding is the presence of an Excel 4.0 macro sheet, indicated by the OOXML_XLM_MACROSHEET heuristic. While the macro content is truncated and heavily obfuscated, its presence strongly suggests an attempt to execute arbitrary code. The likely intent is to download and execute a second-stage payload, a common technique for initial access or further system compromise. Due to the obfuscation and truncation, the exact payload and delivery mechanism cannot be determined with high confidence.

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` `76d972bb36ec26255ecfa797b6e0d1606be9a2161c3fe2a46eb84d1a169a53c1`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	7776 bytes

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