Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 55b4ae264bbd6933…

MALICIOUS

Office (OOXML) / .XLSX

237.2 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-03-11
MD5: 1083ce36f5b5ef2c95c05ab24090b22f SHA-1: cb439efcacd86109150cc00a55af770ab5e16446 SHA-256: 55b4ae264bbd69339965edee9c86a6fb869f3b6f6f693b33f41820f00f30ecd1
180 Risk Score

Malware Insights

Emotet · confidence 95%

MITRE ATT&CK
T1059.005 Visual Basic

The sample is identified as malicious by ClamAV with a signature indicating it is an Emotet downloader. Static analysis reveals the presence of Excel 4.0 macro sheets, which are known to be used for malicious purposes. The heuristics confirm the use of these macro sheets, specifically an international XLM macro sheet hidden within an XLSX file. The primary function of these macros is to download and execute a second-stage payload, consistent with Emotet's typical behavior.

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
e7085ac4bb151e06e68b0fa03406a3caeb756afa2ad3891a5e6a51326a913a61		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 2466 bytes
xlm_sheet_01.bin
294fba96533e16b8e32fcc670b890c44fe9dfc759e5d84743c74026ba7bd4a20		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 428 bytes
xlm_sheet_02.bin
f0daf3cbff097906d4170f35f5f5c2394e9b70d2a487782035c708617ae7b9ec		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet2.bin 428 bytes

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