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

Static analysis result for SHA-256 c816a0e550e4f10d…

MALICIOUS

Office (OOXML) / .XLSX

26.4 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: 150a63879c1fe774db15257efe640cfa SHA-1: 38b05f55001b3a8afe2720b5262419fd4dfdc9f2 SHA-256: c816a0e550e4f10d17342d79c0861cef97d3a5938f99615fa677d6288d44dc71
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

This XLSX file contains Excel 4.0 macros, which is a critical finding. The macros utilize WinAPI functions such as URLDownloadToFileA and ShellExecuteA, indicating an intent to download and execute a secondary payload. The reconstructed URL from the macro is https://revistascientificas.posgradocolumbia.edu.py/ds/3.gif, which is likely the source of the malicious payload.

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. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
  • Binary XLM macro sheet with WinAPI/download strings critical OOXML_XLM_BINARY_WINAPI_STRINGS
    Excel 4.0 macro sheet is stored as BIFF12/XLSB binary data and contains Win32 download or process-execution API strings such as URLDownloadToFileA, ShellExecuteA, or CreateDirectoryA. These strings are high-signal in XLM macro sheets and catch payload-download macros that XML-formula scanners cannot parse.
  • URL reconstructed from XLM cell array (1 URL) critical OOXML_XLM_CELL_ARRAY_URL
    Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell) or inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation. The reconstructed URL is invisible to literal-bytes URL extraction because it is never contiguous in the workbook stream. URLs were recovered by walking the BIFF12 record stream of every worksheet and macrosheet part and decoding RK/inline-string cells in both row-major and column-major order.
  • 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 https://revistascientificas.posgradocolumbia.edu.py/ds/3.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
4be47f6fcaf3ddcd2c09a8b9ee903affb3f4991b54c12b0197126fd22afb2207		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 200547 bytes

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