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

Static analysis result for SHA-256 98db8104575b7b48…

MALICIOUS

Office (OOXML) / .XLSX

65.9 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 8e7345dabae6a460f38a24c15a450319 SHA-1: 5f9fc9bf26d3628a015b7f6ba27156ceef90b72c SHA-256: 98db8104575b7b48a8c94564998bca73339f73fbaac0a89c932bd4639621c339
182 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros that utilize WinAPI functions like URLDownloadToFileA to download files. The macros reconstruct three URLs, which are likely used to fetch a second-stage payload. Although the URLs themselves are marked as confirmed benign, the presence of the macro and download functionality indicates a malicious intent to download and execute arbitrary content.

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/910251809556271117/912318014416912415/XOwuRIcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318020003692574/FqtFBvEOrukvcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318007320145940/XOftdbhXmOZcuntfuck.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
68cce9cdfeefb24a0febd28269a194096fa28d10ff8daea7f73e973a48d87e5b		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5317 bytes

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