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

Static analysis result for SHA-256 24cf97c3e98d3fb3…

MALICIOUS

Office (OOXML) / .XLSM

136.8 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 0e873ae39ec68fcab7c2e4ceead70cd0 SHA-1: 2f0d17e38a45a74bc876f6e2f2f1ac6fbe7323f8 SHA-256: 24cf97c3e98d3fb31ee8f331bc6b990205967ca68679494ab3688c8333cb6773
130 Risk Score

Malware Insights

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

This XLSM file contains Excel 4.0 macros that leverage dangerous functions like FOPEN, FWRITE, FCLOSE, and EXEC. The macros reconstruct a file path: "C:\ProgramData\RxNKFoWEY.vbs". This path is likely used to write a downloaded payload or staging script to disk. The presence of these functions and the constructed path strongly indicate the execution of a second-stage payload. The file is classified as malicious due to these capabilities.

Heuristics 4

  • 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.
  • Dangerous XLM formula APIs: FOPEN, FWRITE, FCLOSE, EXEC, 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.
  • 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
0ea5d5e5ec88e64029c13c04718c0eac2dcee2930a61cec85debfc0182ae8a41		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5887 bytes

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