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

Static analysis result for SHA-256 5e052de6354eedab…

MALICIOUS

Office (OOXML) / .XLSX

84.0 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: f98be94ce99d7705003e01b7635ccba8 SHA-1: 6222b0429c652aa6432c46a4e3cd2bbcdf9c05a5 SHA-256: 5e052de6354eedab9db9c35142723c42e0da1e9d37291b60e427ac35046aa083
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution

The sample contains Excel 4.0 macros that are designed to execute a command to download and run a second-stage payload. The macro reconstructs the command 'wmic process call create 'mshta C:\ProgramData\excel.rtf'', which indicates it attempts to execute a file from the ProgramData directory. The URLs extracted from the macro are likely sources for this payload.

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.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.
  • 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/905513341278093417/905515879897366578/KBSfWgNDPUjg.mp3
    • https://cdn.discordapp.com/attachments/905513341278093417/905515268112023643/JqKeifcHkSNnh.mp3
    • https://api.onedrive.com/v1.0/shares/u!aHR0cHM6Ly9vbmVkcml2ZS5saXZlLmNvbS9lbWJlZD9yZXNpZD03ODE0RkU0MzMyMzBBOERBJTIxMTM5JmF1dGhrZXk9IUFPYm85ZFZBU29Fc3JBYw/root/content

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
eb10cc73a45d6884db283ceb1a8e18d187c4b376ad2aaff2119abdc5de21f445		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 271684 bytes

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