Office (OOXML) / .XLSX malware analysis — malicious · 41689cd47c7f6dc6

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 96cc5434bc4c3b9d386dbc991acca321 SHA-1: 91b1672bc8c544d7983f47c168ac0709461cff2c SHA-256: 41689cd47c7f6dc652c0a50093e7810595972457d86dffacc4341b5ed600e54d

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 an XLSX file. The extracted macro content, though truncated and partially obfuscated, shows evidence of attempting to construct a file path 'C:\ProgramData\excel.rtf' and execute it. This suggests the macro's purpose is to download and execute a second-stage payload from a remote source, which is a common initial access technique.

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` `b7e94a5c147034e431651289ac9976a648735073533774d9cf847d44ed8325c1`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	360933 bytes

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