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

Static analysis result for SHA-256 fa4db4bc9c8c7d0b…

MALICIOUS

Office (OOXML) / .XLSX

26.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: fbcee206a02b7ed1b94bf1bd67f34981 SHA-1: 2893705c6e94e0dc845874dc9be1cc4bc1ac1006 SHA-256: fa4db4bc9c8c7d0b571f6f624b8498c001c370543bfedb482e18a8c1f2553c82
182 Risk Score

Malware Insights

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

The file contains Excel 4.0 macros, which are known to be used for malicious purposes. The macros contain strings like URLDownloadToFileA, DownloadToFileA, and ShellExecuteA, indicating an intent to download and execute a file. The reconstructed URL from the macro is https://mfruits.co/ds/4.gif, which is likely the source of the second-stage payload. The use of these WinAPI functions strongly suggests the macro's purpose is to download and run an executable.

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://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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