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

Static analysis result for SHA-256 3261d993a60b2f43…

MALICIOUS

Office (OOXML) / .XLSX

26.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: f74a81ef9061ea21fed357c8daf63ad9 SHA-1: 6e1776136d2604200e38bafb2e6b4a2d8d9c6c50 SHA-256: 3261d993a60b2f4302727343a03c25ddeadbd2a0f32134b3ce45e999dcecbadb
182 Risk Score

Malware Insights

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

The file contains an Excel 4.0 macro sheet, which is highly suspicious. The macro sheet includes strings indicative of downloading and executing a file, such as URLDownloadToFileA, DownloadToFileA, and ShellExecuteA. The embedded URL https://mmsu.com.ua/ds/4.gif is likely used to fetch a second-stage payload. The macro sheet's structure and embedded WinAPI strings 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://mmsu.com.ua/ds/4.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
f3468520ab7f9a1917dad4e3092f53f9cc8f20ff090c54c05de4742347202530		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 197532 bytes

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