Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 8b52fd402fa59d23…

MALICIOUS

Office (OOXML) / .XLSX

21.1 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-04-19
MD5: 3cb97231073b82d5fbbc646e589754f8 SHA-1: 0bef95589e7c2749b093d97ac0a6419c6f21f6c9 SHA-256: 8b52fd402fa59d23079970babe53602a49434bbf27bebaa250bbde9b7764a42d
250 Risk Score

Malware Insights

Emotet · confidence 95%

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1059.001 PowerShell T1105 Ingress Tool Transfer

This Excel 4.0 macro-enabled workbook contains critical heuristics indicating the use of dangerous formula APIs like FORMULA, which are known to download and execute payloads. The macro code reconstructs the string 'r"&eg"&s"&vr3"&2.e"&x"&e' and attempts to save it to '\Windows\SysWow64\'. It also includes multiple URLs, such as 'http://buchhave.net/cache/t82rF5S/', which are likely used to fetch the second-stage payload. The ClamAV detection as 'Xls.Downloader.Emotet03220-9941789-0' strongly suggests an Emotet family infection.

Heuristics 6

  • 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.
  • Excel 4.0 Auto_Open defined name critical OOXML_XLM_AUTOOPEN_DEFINEDNAME
    Workbook defines _xlnm.Auto_Open or _xlnm.Auto_Close while containing an XLM macro sheet. This is the OOXML/XLSB auto-execution shape for Excel 4.0 macros.
  • Dangerous XLM formula APIs: FORMULA critical OOXML_XLM_DANGEROUS_FN
    Excel 4.0 macro sheet uses formula APIs that call directly into Win32 (=CALL/=EXEC/=REGISTER/=FORMULA). These are the primitives used to download payloads, write files, and start processes from an XLM macro without invoking VBA.
  • ClamAV: Xls.Downloader.Emotet03220-9941789-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Emotet03220-9941789-0
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 4 hidden sheet(s) — hidden sheets are commonly used to conceal macro code, staging data, or intermediate payload construction
  • Embedded URL info EMBEDDED_URL
    One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
    URL http://buchhave.net/cache/t82rF5S/
    • https://www.bilandecompetences.fr/administrator/3c/
    • http://bostonseafarms.com/images/zPgXFMy8VbKNXtFp/
    • http://casazulshop.com/Adapter/yJTgSEDEpQvm/
    • http://bruiserbodies.com/images/vAj7fuqYe5y9/
    • http://brittknight.com/PHP/f/
    • http://carloshd.com/trulia/4vsUaqQd/
    • http://schemas.openxmlformats.org/spreadsheetml/2006/main
    • http://schemas.microsoft.com/office/excel/2006/main
    • http://schemas.openxmlformats.org/officeDocument/2006/relationships
    • http://schemas.openxmlformats.org/markup-compatibility/2006
    • http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac
    • http://schemas.microsoft.com/office/spreadsheetml/2014/revision
    • http://schemas.microsoft.com/office/spreadsheetml/2015/revision2
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision3
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision6

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
f9ef0dd03a642623a126a648a3e3b498d8403d13558799b8b55ca81a239f78e5		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.xml 3968 bytes

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