Malicious Office (OOXML) / .XLSM — malware analysis report

Static analysis result for SHA-256 fa7caa53e7421aa7…

MALICIOUS

Office (OOXML) / .XLSM

236.3 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 6f2c5c1b5ffecf9fdad39c798c866aa5 SHA-1: 89353397d2cffed80bf6463a4be0e36d29044198 SHA-256: fa7caa53e7421aa7a72ee09be195e980678022f0760f052d59621c435d965f81
250 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1204.002 Malicious File

The file is an XLSM document containing Excel 4.0 macros. Critical heuristics indicate the use of dangerous XLM functions like FOPEN, FWRITE, FCLOSE, EXEC, and REGISTER, which are used to download and execute payloads. The macros construct a path to a script file, 'C:\ProgramData\lHIfiBphyRKyMb.sct', and then use the EXEC function to run it. This indicates a downloader or dropper functionality.

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: FOPEN, FWRITE, FCLOSE, EXEC, HALT 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.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 1 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://schemas.openxmlformats.org/spreadsheetml/2006/main
    • http://schemas.microsoft.com/office/excel/2006/main
    • http://schemas.openxmlformats.org/officeDocument/2006/relationships

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
33c1a5e50d470a1074d50bf430207a96c8e5c56d47f068c7206514a302f64a2d		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 714393 bytes

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