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

Static analysis result for SHA-256 58c6ec9f5698e140…

MALICIOUS

Office (OOXML) / .XLSX

26.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: b2ec1783b7ca7ef45d0f2a5b770bc7df SHA-1: 15c5ece5be6c83eea339cba15c845d0f5740db0a SHA-256: 58c6ec9f5698e14044abd5b70e70303ed2ea73f4e4e1d099e3acb8e1d6b1e0ef
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic for Applications T1204.002 Malicious File

The sample contains critical heuristic firings indicating the presence of Excel 4.0 macros that utilize WinAPI functions for downloading and executing files. Specifically, the macro reconstructs the URL 'https://ruth.co.il/ds/4.gif' and uses functions like URLDownloadToFileA and ShellExecuteA, strongly suggesting it's designed to download and run a second-stage payload. The embedded URL is the primary IOC.

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://ruth.co.il/ds/4.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
0e69ba788cb3ffb490d766a0bc85cd4b0a0356528b4e74b33b0d6e539f811dc9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 197528 bytes

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