Office (OOXML) / .XLSX malware analysis — malicious · 4d5b6c4e1b5a1add

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 93fb617b3ff2a79088847845c0d2cf7f SHA-1: 40f67f93144ce0b249c8d91a745fb832207a1ee7 SHA-256: 4d5b6c4e1b5a1addbe652779e83c367b0f1f3edc736ea28d81f63157ccb54055

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The file is an Excel 4.0 macro sheet, indicated by the OOXML_XLM_MACROSHEET heuristic. The embedded macro sheet contains obfuscated strings that appear to construct a file path, 'C:\ProgramData\excel.rtf'. This suggests the macro is intended to write or execute a file from this location, likely as part of a multi-stage attack. The exact execution flow is unclear due to the truncated script data, but the presence of Excel 4.0 macros points to a common delivery mechanism for malware.

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` `645730153d6a95647d12984ea00417b3501b3f02ca1d311fbfc47e8033cafae9`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	283382 bytes

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