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

Static analysis result for SHA-256 660f1e8b698bbb6d…

MALICIOUS

Office (OOXML) / .XLSX

26.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: f821880152826f3d2b18a0b60589858d SHA-1: 5aae377b1fc46691b0f0d77edd844cbb5d7280b2 SHA-256: 660f1e8b698bbb6df307d8d42d0a68421817c4b625bf5e79db278bff4a8594e6
242 Risk Score

Malware Insights

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

The sample is an Excel file containing Excel 4.0 macros. These macros are designed to download a payload from the URL 'https://mfruits.co' and execute it. The macros utilize WinAPI functions such as URLDownloadToFileA and ShellExecuteA to achieve this. The specific payload and its ultimate purpose are not detailed in the provided evidence, but the mechanism is clear.

Heuristics 5

  • 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.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.
  • URL reconstructed from XLM cell array (2 URLs) 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://mfruits.co
    • https://mfruits.co/ds/4.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
3cc9fed58ee9e6f90f441cf973e0eb01b2c7575a317a07b7ad67aefbf5f18ddf		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 197528 bytes

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