Emotet — Office (OOXML) / .XLSX malware analysis

Static analysis result for SHA-256 51a6aef9e44bb09d…

MALICIOUS

Office (OOXML) / .XLSX

68.9 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: 2929b1ca573ce31c3ff0fb72ef065fd4 SHA-1: 06b04890ef7b57298723b464931337acb7085fa6 SHA-256: 51a6aef9e44bb09d7133889728eb6c49450c41ed5df9fb9d6308f7fb441526d7
290 Risk Score

Malware Insights

Emotet · confidence 95%

MITRE ATT&CK
T1059.005 PowerShell T1218.011 Signed Binary Proxy Execution: Rundll32 T1059.001 PowerShell T1105 Ingress Tool Transfer

The sample utilizes Excel 4.0 macros, specifically leveraging dangerous functions like FORMULA and RETURN, to achieve its malicious objectives. The macro is designed to download and execute a second-stage payload using rundll32.exe and the urlmon.dll component. The reconstructed string 'D"&"l"&"lR"&"egister"&"Serve"&"r' indicates the intent to register a downloaded component, likely an executable or DLL, from one of the provided URLs. The ClamAV detection as 'Xls.Downloader.EmotetExcel02221-9938627-0' strongly suggests the Emotet family.

Heuristics 7

  • 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, RETURN 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.EmotetExcel02221-9938627-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.EmotetExcel02221-9938627-0
  • LOLBin token sequence in document text high SE_LOLBIN_RUN_COMMAND
    Extracted document text contains a Windows script/execution tool name (PowerShell, mshta, cmd, rundll32, regsvr32, …) within 220 characters of a dangerous flag, command verb, or URL. This is a visible 'run this' instruction in HTML/PDF/RTF lure bodies, or — in macro-laden Office files — the macro's own string-pool entries appearing adjacent in extracted text.
  • 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://thereliableprofessionals.com/ALFA_DATA/nuUv5Mt6oySnaB3EU/
    • https://new.kameeztor.com/elementor-pro/leH/
    • http://h5.l2saga.net/wp-content/uploads/FqnWeRNxxsUcb/
    • https://hotrotamlythpt.org/4sxlc/hKWQyF4fe5VO9t7vi/
    • https://nuno.studio/cgi-bin/CzaqtBSuGwn9SW7cn/
    • 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
d810cc87eb589e5f09a9a5cb06e9b818ff37e1b4d0032ba08fbf4b3620a5d223		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.xml 3431 bytes

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