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

Static analysis result for SHA-256 5a2e283ef238172e…

MALICIOUS

Office (OOXML) / .XLSX

77.7 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: bb816b6c1d2e442eda4da5a998b95295 SHA-1: 58c3488042a58fcb6e2677fe38e443baef46904b SHA-256: 5a2e283ef238172eaffebf3bb9691bc846e072b7d6e831ec9dc9ed72aaff4061
182 Risk Score

Malware Insights

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

The file contains Excel 4.0 macros that are designed to download and execute a payload. The macros reconstruct a URL and a file path for saving the downloaded content. Specifically, the macro attempts to download a file from 'http://1514.185.205:808/QW5VWUFL5VQ7QPETG3CTYX2Z4R25PC' and save it as 'C:\ProgramData\BMCTmTQTkuu.rt'. The presence of multiple Discord URLs suggests potential fallback or alternative download locations for the 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 http://1514.185.205:808/QW5VWUFL5VQ7QPETG3CTYX2Z4R25PC
    • https://cdn.discordapp.com/attachments/912720368844824620/913069632129212466/reSCeFOYjZtCtkOyellowfacebrownietacohead.ogg
    • https://cdn.discordapp.com/attachments/912720368844824620/913069669341069452/jPzSCuyellowfacebrownietacohead.ogg
    • https://cdn.discordapp.com/attachments/912720368844824620/913069652077326346/KftJXyrZQyellowfacebrownietacohead.ogg

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
c595d0bfc121d35f53e760649dc585d51f5ba398cccf8518b79b837d51183e15		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 8020 bytes

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