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

Static analysis result for SHA-256 dea001cf8cf2cd29…

MALICIOUS

Office (OOXML) / .XLSM

270.9 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: f231e4902c9ad546d75482f4e2e95b9f SHA-1: 07d8b8dc13a829ce10edbe25d2195dee4fdf20c9 SHA-256: dea001cf8cf2cd2925312752a72b42eba054a0f5c67918bad6e7eebaf3c2e5d5
190 Risk Score

Malware Insights

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

The sample is an Excel 4.0 macro-enabled spreadsheet. It uses the FOPEN function to open a file at C:\ProgramData\bCWRXb.sct and the EXEC function to execute it. This indicates a downloader or dropper functionality, aiming to execute a second-stage payload. The specific functions used and the file path suggest a custom or less common malware delivery mechanism.

Heuristics 5

  • 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.
  • 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
1906d56cde463ab9cb7dbc1d9a28450787d213740a4634596fe2d49dca8c4c7e		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 882706 bytes

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