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

Static analysis result for SHA-256 ca1d5b8e47180171…

MALICIOUS

Office (OOXML) / .XLSX

53.1 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 113ec4e2c91560aa0b713dac5a9ec33b SHA-1: 3ab867081c9b2b6c4dd6dafd5dc8f26979d830d6 SHA-256: ca1d5b8e471801715b20b4c38152ce0df036402607243361dbc05c4b618b843f
182 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros, which are known to be used for malicious purposes. The macros utilize the URLDownloadToFileA WinAPI function to download files from three distinct URLs. These URLs are reconstructed from the macro's cell array. The downloaded files are likely second-stage payloads. The macro's intent is to download and execute arbitrary code from the internet.

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/911259060106559531/912320793264947240/QmnwGJVXeRcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/910251809556271117/912318798151942155/ftygFcuntfuck.mp4
    • https://cdn.discordapp.com/attachments/911259060106559531/912320754304041000/JsnIPhDNjiicuntfuck.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
b7c2b6c6e30e3d5dba966ac8f882057db2b0fa16d648d1a9f92b1208f6b76d7d		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5395 bytes

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