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

Static analysis result for SHA-256 627b7cbe3e00c572…

MALICIOUS

Office (OOXML) / .XLSX

95.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 4d9deeffe038b6193b97a3938faee9db SHA-1: 56169777d9697a1a66b85c5329684aed638a5968 SHA-256: 627b7cbe3e00c572b27efb0acbae397deca3904ff78e9e4cffd2ad18f76e4e53
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution T1566.001 Spearphishing Attachment

The sample contains Excel 4.0 macros that are designed to execute a command using 'mshta' to download and run a file from a provided URL. The macro explicitly calls 'wmic process call create 'mshta C:\ProgramData\excel.rtf'', indicating it attempts to download and execute a second-stage payload. The URLs provided 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/905513341278093417/905515575902625802/pEmmK.mp3
    • https://cdn.discordapp.com/attachments/905473607621296159/905482718320676894/Gyqzr.mp3
    • https://cdn.discordapp.com/attachments/905474057821093941/905482295702601759/ihwtzGrsWjEHFM.mp3

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
5c4abc2fd734ce2b56de394e94a46a517e19c28d6221112e09411cf1b840b5c3		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 281653 bytes

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