Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 91f789d4a38dc49d…

MALICIOUS

Office (OOXML) / .XLSX

61.0 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 91f635dd1e8c3ed4feacea6c32c593a1 SHA-1: e3d2d5a005b56a9b531d54ec2958dd992182fe72 SHA-256: 91f789d4a38dc49dcc2259be49ac6ebce17bf9c2a74418978a6fabc40a05bd16
60 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic

The sample is an Excel file containing a macro sheet. The macro sheet appears to be attempting to write a file to 'C:\ProgramData\excel.rtf'. This suggests a downloader or droppper functionality, where the macro is intended to fetch and execute a secondary payload. The macro content is heavily obfuscated and truncated, limiting further analysis of its exact behavior.

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.

FilenameKindSourceSize
xlm_sheet_00.bin
416855ed1a0337e238fc2600ce3f2cb15baed1628ec5ebb2ef379f8ae72c1087		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 152666 bytes

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