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

Static analysis result for SHA-256 1197a1dbefe82638…

MALICIOUS

Office (OOXML) / .XLSX

63.0 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: c69697ae58dc57de3f282809a41e7be6 SHA-1: b6c051a303662b3ee6528325ee4094f9596be667 SHA-256: 1197a1dbefe826385c896d9bb108a74cd671b7469bb8b94c8536f7fe037dc7c3
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1218.010 System Binary Proxy Execution: Regsvr32 T1566.001 Spearphishing Attachment

The sample contains Excel 4.0 macros that reconstruct and execute the command 'mshta C:\ProgramData\excel.rtf'. This command is designed to download and execute a remote HTML Application from one of the embedded URLs. The use of XLM macros and the execution chain strongly suggests a malicious document intended to deliver a secondary 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/907663849111556109/907974897421144104/WnbBZwQx.mov
    • https://cdn.discordapp.com/attachments/907663849111556109/907974770048503838/qnwEGLbVCO.mov
    • https://cdn.discordapp.com/attachments/906996518161113190/907981556390436874/ODYyLtKlsNhDhT.mov

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
c9f01ebaca9090909e5601579d9d6d8be10d9f4a0563c4cba176a80780065e9b		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 57441 bytes

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