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

Static analysis result for SHA-256 18bd1ae701ff57a6…

MALICIOUS

Office (OOXML) / .XLSX

234.8 KB Created: 2021-02-03 15:28:44 UTC Authoring application: Microsoft Excel 16.0300
MD5: 3489702c1298d45a5964aadd4a5753a6 SHA-1: ed0afe8cbdfb77332f9ce8c28b1be592eb89d730 SHA-256: 18bd1ae701ff57a6d1119f18c53350688f41cbac0ea1ad0cb73234f6ab733404
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The file is an Excel spreadsheet containing Excel 4.0 macros, as indicated by the OOXML_XLM_MACROSHEET heuristic. The ClamAV detection name 'Xls.Downloader.DarkTheme122101-9913615-0' strongly suggests a downloader functionality. The embedded XLM macro sheet, though truncated, likely contains code to fetch and execute a secondary payload, aligning with the downloader pattern.

Heuristics 2

  • 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.
  • ClamAV: Xls.Downloader.DarkTheme122101-9913615-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.DarkTheme122101-9913615-0

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
f6b740bb41cad4841c727c3de2d9a5f0b7f72367dd60b62942283b39ca2a6dbf		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 141726 bytes

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