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

Static analysis result for SHA-256 67d5d7c0fd9cf2c0…

MALICIOUS

Office (OOXML) / .XLSX

292.2 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: c3b6eaa54ce624dea50bd3726cb2d02d SHA-1: 80409a02c2e6cfa8f8790ecac92a176518a4d8c3 SHA-256: 67d5d7c0fd9cf2c06c7fb727e22403b57547c4c00b2a6c58df038c4e2ac8e61b
242 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1105 Ingress Tool Transfer

The file contains Excel 4.0 macros, identified by critical heuristics indicating the presence of WinAPI and download strings. These macros are designed to reconstruct and download a payload from the URL https://icgz.co.zw/ds/12.gif, likely executing it as a second-stage attack. The use of XLM macros and the download functionality points to a downloader or droppper malware.

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 (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://icgz.co.zw/ds/12.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
61533e2a12e00326d53033989b1bdb00e9e34b096600977e87a39cb660e5e51b		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 197374 bytes

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