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

Static analysis result for SHA-256 8ca5f41a7c993cbd…

MALICIOUS

Office (OOXML) / .XLSX

67.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 79f84a0182bf1ca3df3247f99ed052fa SHA-1: 122770d01a323334001dbe54fd86daaa319a47a2 SHA-256: 8ca5f41a7c993cbd845a97d772b947b38c88d1a41c0823f0bbb93edfebc32999
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1059.001 PowerShell

The file contains Excel 4.0 macros that utilize WinAPI functions such as URLDownloadToFileA to download a second-stage payload. The macros reconstruct three URLs from cell arrays, which are then used to fetch the payload. Although the extracted URLs are currently marked as confirmed benign, the presence of macro-based download functionality indicates a malicious intent. The specific family is not identifiable from the available evidence.

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 (3 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://cdn.discordapp.com/attachments/911261535769362435/912322787740356678/RXCSzXKTcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/911259060106559531/912320482311819324/CEDdcDbcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318517712416818/XtHZqrUCcuntfuck.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
0e43b5ffa4fd9e8bd29b09b3a113bf031eb21abac83c326767bc95896b02f5fb		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 4705 bytes

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