Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 bf1c8f3fc5e0e557…

MALICIOUS

Office (OOXML) / .XLSX

237.8 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-03-14
MD5: 56020adb54cbf82bcc0e86e7f5f5b10f SHA-1: 2145beb4c570ad2f44fc6c2a8cfcae31876e4f0b SHA-256: bf1c8f3fc5e0e55753fc6b07b55a18927ff43bf08d245737b787496d7c9ca622
180 Risk Score

Malware Insights

Emotet · confidence 95%

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

The sample is identified as malicious by ClamAV with a signature indicating it is an Emotet downloader. Heuristics confirm the presence of Excel 4.0 macro sheets within the OOXML structure, which are commonly used for initial payload delivery. The embedded macro sheets, though truncated in the provided evidence, are consistent with the typical behavior of Emotet for downloading and executing further stages.

Heuristics 3

  • Excel 4.0 macro sheet (3 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 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
9b1fdef6d0824498699cd736122a46adfba44045a4853cccb8773fbc78a32fc3		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 2118 bytes
xlm_sheet_01.bin
76bb729a3fef1962dba3c4d4608bc67767a415d3068cfaefbab6dc04307f5716		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 428 bytes
xlm_sheet_02.bin
e107436a5f0bb0a25f454c2c3756c9b0d1befa58088a66751c1bc69dc47f10ec		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet2.bin 428 bytes

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