Office (OOXML) / .XLSX malware analysis — malicious · c6bdcd1bf20edaf2

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: b70dcc15617c14f7e29fb184cf5f3d0b SHA-1: bca5da40d2fc0d53314642a9da3adca05ba17f4a SHA-256: c6bdcd1bf20edaf288e357f904d6480a661f8e235233c886b2e5866ac8c6ce92

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Service Execution: Service Execution

The critical heuristic firing indicates the presence of an Excel 4.0 macro sheet. Analysis of the macro content reveals a command to execute 'mshta' with a specific file path, 'C:\ProgramData\excel.rtf'. This strongly suggests the macro's purpose is to download and execute a secondary payload disguised as an RTF file from a remote source, likely initiated by the 'mshta' command. The file is an XLSX, which can contain these older macro types.

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` `f6596f4cad31f1a51d2ce0146f8421f9becdabb2283f872b8d0104748cf5b1aa`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	177532 bytes

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