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

Static analysis result for SHA-256 8b5e8b6bec59658b…

MALICIOUS

Office (OOXML) / .XLSX

26.3 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: 60c78db6cf1134c1897245c6fb52db59 SHA-1: 7984532ac72fc1d546707d93f360e7edb989d4de SHA-256: 8b5e8b6bec59658b6a4ce7e97f694ff6f38cfdcbcb991e7db13a2d49388a95ef
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1059.001 PowerShell T1059.003 Windows Command Shell

The sample is an Excel file containing Excel 4.0 macros. Heuristics indicate these macros contain WinAPI strings such as URLDownloadToFileA, DownloadToFileA, and ShellExecuteA, suggesting an attempt to download and execute a secondary payload. The macro reconstructs the URL https://columbia25.aula-web.net/ds/3.gif, which is likely used to fetch the payload. The presence of these WinAPI calls and the reconstructed URL strongly indicate a malicious downloader.

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://columbia25.aula-web.net/ds/3.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
6651bdb46904db7afdc3e5576514edde72d47967bab1a40096ef116c3930aae0		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 200467 bytes

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