Office (OOXML) / .XLSX malware analysis — malicious · 372fc6bc59b240aa

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 61d1a2f2a061d1085cc70323052e1ef6 SHA-1: 4cb6d03b8b3ff4f15c51d3d20b270d9f77ff3575 SHA-256: 372fc6bc59b240aa788c8bae3529d978588a6b931fef13673946a95a2e2e82b8

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The sample is an Excel file containing embedded Excel 4.0 macros, indicated by the OOXML_XLM_MACROSHEET heuristic. The macros appear to be designed to execute a second-stage payload, likely by writing and running a file named 'excel.rtf' from the 'C:\ProgramData\' directory. The content of the macros is heavily obfuscated, but the file path suggests a download and execution chain.

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` `c07052669d5de4ae8acced41ad594b2fd33441018c5dae6aec6cfcebe08f4ae1`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	98574 bytes

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