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

Static analysis result for SHA-256 fdcc23c2a5274d3c…

MALICIOUS

Office (OOXML) / .XLSX

71.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 3732489d7c7933440388bb814d9a8a82 SHA-1: 52095779c8f2dda3b96b303cae2af4f818279428 SHA-256: fdcc23c2a5274d3cca1c78c0ece800207b6434c87d7d888c283211ddcfc3a6d0
182 Risk Score

Malware Insights

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

The sample is an Excel file containing Excel 4.0 macros. These macros utilize WinAPI functions such as URLDownloadToFileA to download files from the provided Discord URLs. The reconstructed URLs are the primary indicators of compromise. The macro's intent is to download and execute a second-stage payload, which is a common delivery mechanism for malware.

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

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
2e45ef7a0c1a0170c3820b851ea7c7d73b8ed80bcf57d00ab8ff59f1e92de376		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 5973 bytes

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