Emotet — Office (OOXML) / .XLSM malware analysis

Static analysis result for SHA-256 f744479f99039004…

MALICIOUS

Office (OOXML) / .XLSM

21.2 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-03-17
MD5: f17ae261d4d2a9b18a70e6ade60fe5f8 SHA-1: 7a58f39ef793532b60b7ba9c6023d0cd8ca9af5f SHA-256: f744479f9903900438136774cc203c44c16b71ec26973509aef3aac0ee891a7a
250 Risk Score

Malware Insights

Emotet · confidence 95%

MITRE ATT&CK
T1059.005 Service Execution: Visual Basic T1059.001 Command and Scripting Interpreter: PowerShell T1204.002 Malicious File: User Execution: Malicious File T1105 Ingress Tool Transfer

This XLSM file utilizes Excel 4.0 macros, specifically leveraging the FORMULA API, to download and execute a payload. The macro constructs a URL from concatenated strings and saves the downloaded content as 'rfs.dll' in the \Windows\SysWow64\ directory, then attempts to execute it as 'regsver32.exe'. The ClamAV detection and the presence of multiple suspicious URLs strongly indicate Emotet activity.

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://beetle-j.jp/wp-admin/ErM4mW05tdj/
    • http://e3technology.in/2checkout_integration_php/rDcr1Wl90WWA9M/
    • http://bjornbol.dk/wp-includes/ve4cnkjsUMWXC5Cb2bJ/
    • http://bebesel.com.tr/cgi-bin/1wy3oHO/
    • https://brutobrasil.com.br/pdf/toO18cIP3/
    • http://biesenbeek.nl/familie/b6KKlrfH75GD3dHojB/
    • http://bcelectronics.co.za/wp-content/grKnz1V/
    • 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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