Office (OOXML) / .XLSX malware analysis — malicious · 9c3b9ec2b8e0983c

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: b1d71f6899b616486e6ac29650a34419 SHA-1: 13e1aa8c5b2cd1b8e1aedee3e236ac4f9f8b112b SHA-256: 9c3b9ec2b8e0983cecd56d1358048351eaf26e5232d8be2fc1cab02a7c5919d4

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The file is an Excel document containing Excel 4.0 macros, as indicated by the OOXML_XLM_MACROSHEET heuristic. The macro code appears to be attempting to write a file to 'C:\ProgramData\excel.rtf'. This is a common technique for dropping and executing secondary payloads. The macro content is heavily obfuscated, making it difficult to determine the exact execution flow or final payload.

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` `e3a635718e8487366c18b07e58ad1b94cc0f329a35434c5b7cc07eabde093796`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	94312 bytes

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