Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 9d41bc2f5adca72b…

MALICIOUS

Office (OOXML) / .XLSX

192.2 KB Created: 2021-11-18 12:27:29 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-05-04
MD5: eb5d651a73d62d5f5f6340c826e40a31 SHA-1: 8bb244730c176b8dd1a98b17030b9cd4c5948396 SHA-256: 9d41bc2f5adca72ba0f261bfd3c9fd77d40a94e2f1ef7b083137435986da0d93
200 Risk Score

Malware Insights

Emotet · confidence 95%

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

The sample is an Excel file containing Excel 4.0 macros, a known delivery mechanism for Emotet. The critical heuristic 'OOXML_XLM_MACROSHEET' and the ClamAV detection 'Xls.Downloader.Emotet-OOXML_XL-af43432fbcb8603c-9980048-0' strongly indicate Emotet. The macrosheet 'xl/macrosheets/intlsheet1.bin' likely contains code to download and execute a secondary payload.

Heuristics 4

  • 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
  • External relationship medium OOXML_EXTERNAL_REL
    External target in xl/externalLinks/_rels/externalLink1.bin.rels: /fy.xlsx

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
15318fc071b59cdcd90a77709f1743574b4541b72c53fd75f7ea8b20543b1a19		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 14061 bytes

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