Office (OOXML) / .XLSX malware analysis — malicious · c6699521e44baeb6

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 12cf566fa81615faa7a0d1c3705ecd9f SHA-1: 944f87aaaa10e1eb9753fc8b97a329cc17059539 SHA-256: c6699521e44baeb604973c75b6392c68dc82a7ec43f65e2710b3fe000abd8b62

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an Excel file containing a macro sheet, indicated by the OOXML_XLM_MACROSHEET heuristic. The embedded macro sheet contains obfuscated commands that appear to construct a path to a directory and a filename ('rtf'). This suggests the macro's purpose is to download and execute a second-stage payload from a remote location, likely exploiting the constructed path. The family is unknown due to the lack of specific indicators.

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` `9d324d8d8b3cc56e4bd3ad9973074e89927175f2ee7680c0a6f21e36a3e6cce2`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	3726 bytes

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