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

Static analysis result for SHA-256 98fd6650047c6f31…

MALICIOUS

Office (OOXML) / .XLSX

26.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: e2b7b23d05e984a1c9b5e8f81361067c SHA-1: 50fbda9020b1de74c9cfaa8034af43d781e662cd SHA-256: 98fd6650047c6f318af8f01980d4e76dcc1297f8655c7c2db41b323e5a9d7238
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1071.001 Web Protocols

The file contains Excel 4.0 macros, which are known to be used for malicious purposes. The macros contain strings like URLDownloadToFileA, DownloadToFileA, ShellExecuteA, and CreateDirectoryA, indicating an intent to download and execute a file. The macro reconstructs the URL https://kacedu.in/ds/4.gif, which is likely used to fetch the second-stage payload. The presence of WinAPI strings and the reconstructed URL strongly suggest a downloader functionality.

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://kacedu.in/ds/4.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
4d3267d5cb48a24d8d5a76370a2eebaf0d0fae662a1ae41551cbc28e948767c7		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 197524 bytes

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