Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 cf761c1eff73ee36…

MALICIOUS

Office (OOXML) / .XLSX

264.4 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-02-21
MD5: a791f9e65b7f4bb9cc98aad22c8baa76 SHA-1: bc07d6efa888e55d5da98c66f3b28924e44d907b SHA-256: cf761c1eff73ee3669d04b86f262a1b1fde72bb66718c3ce5693dea0af5fd231
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 the signature Xls.Downloader.Emotet-OOXML_XL-af43432fbcb8603c-9980048-0, indicating it is an Emotet downloader. The presence of Excel 4.0 macro sheets (xl/macrosheets/intlsheet1.bin, xl/macrosheets/sheet1.bin, xl/macrosheets/sheet2.bin) strongly suggests the execution of malicious macros. While the macro content is truncated, the heuristic firings and the ClamAV signature confirm its role as a downloader, likely for a second-stage Emotet payload.

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
82eb811fec733a2780dd52416cbfe418d752bbc9bbf9e24e79fa26d105fa2576		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 2451 bytes
xlm_sheet_01.bin
cceb5eb124456a2baf0d7337d02e6820fa47434400ba86b106524f5e3caffa74		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 484 bytes
xlm_sheet_02.bin
0d40597c4277bdac7b862f939abbb3f94c58fcf4784bf9f537f04dcb34e67759		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet2.bin 484 bytes

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