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

Static analysis result for SHA-256 1a1024ddf268323a…

MALICIOUS

Office (OOXML) / .XLSX

88.2 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: ea7426317c012c8b8d32ab0640f9a0a2 SHA-1: b655e44ddef810c79ed835dd7577d877ea3fc05e SHA-256: 1a1024ddf268323ab5746ed2543a2916145086c8c05bee784e32b3bf71867be6
182 Risk Score

Malware Insights

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

The sample is an Excel 4.0 macro sheet that contains strings indicative of WinAPI calls for downloading files, specifically URLDownloadToFileA. The macro sheet reconstructs three URLs which are likely used to download and execute a second-stage payload. Although the URLs themselves are marked as confirmed benign, the presence of the download functionality within the macro sheet strongly suggests malicious intent. The script content is heavily obfuscated and truncated, preventing a more detailed analysis of its execution flow.

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/910251809556271117/912318681067958312/apYJdKuUJRxcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318504923988028/FxqQBcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/911261535769362435/912322756757061693/KkFbocuntfuck.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
e5b5f7f998ce9ee40bf37d14b6b4625f434dacf77e67ba0c1dafa48929a6de65		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5661 bytes

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