Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 ecee63b6a0b8a9da…

MALICIOUS

Office (OOXML) / .XLSX

135.6 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: c26eed2d38d3a15335598c0b170cd8d6 SHA-1: 22e94754c78ca22912c16eea29d778d48bb5bbd5 SHA-256: ecee63b6a0b8a9daba189462a03c0373928c84ed737a1e34f2e1830f64b177ad
180 Risk Score

Malware Insights

Emotet · confidence 95%

MITRE ATT&CK
T1059.005 Visual Basic

The sample is an XLSX file containing an embedded Excel 4.0 macro sheet, as indicated by the OOXML_XLM_MACROSHEET and OOXML_XLSB_INTL_MACROSHEET_IN_XLSX heuristics. ClamAV detection confirms this as Xls.Downloader.Emotet-OOXML_XL. The presence of the XLM macro sheet suggests it is designed to execute code, likely to download and run a second-stage payload. The specific macro sheet file is xlm_sheet_00.bin.

Heuristics 3

  • 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.
  • XLSB international XLM macro sheet hidden in .xlsx critical OOXML_XLSB_INTL_MACROSHEET_IN_XLSX
    OOXML package is named .xlsx but contains XLSB workbook parts and an international Excel 4.0 macro sheet. This hides XLM macro execution from scanners that trust the extension or only inspect XML worksheet parts. The technique is macro execution, not a document-parser CVE.
  • ClamAV: Xls.Downloader.Emotet-OOXML_XL-af43432fbcb8603c-9980048-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Emotet-OOXML_XL-af43432fbcb8603c-9980048-0

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
e211bc8384b61ceb3c2f952e9869fef2f7cc488f3128253772792a2ecd7a5adc		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 1823 bytes

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