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

Static analysis result for SHA-256 69fe1bc03e4fc0a7…

MALICIOUS

Office (OOXML) / .XLSX

76.1 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 5b3a5c210da6c92ad1b28c057fb33808 SHA-1: 922822e5c237a2c3006b2caea28936d5d9382943 SHA-256: 69fe1bc03e4fc0a7c9ca0466cb3cc352c7446b27a4ddb466ba93aeae4fbac7df
182 Risk Score

Malware Insights

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

The sample contains Excel 4.0 macros that reconstruct a path to mshta.exe and a filename 'rCVuy.rtf' in C:\ProgramData. The macros also reconstruct multiple URLs hosted on the Discord CDN, which are likely used to download and execute the second-stage payload. The use of XLM macros and the download-and-execute pattern are indicative of a downloader 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.
  • 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/912726182980624406/913011988488151071/VREcGZRvOYEWbeanerwopnigga.ogg
    • https://cdn.discordapp.com/attachments/912726182980624406/913011980036616192/LWGHEbeanerwopnigga.ogg
    • https://cdn.discordapp.com/attachments/912726182980624406/913011996872552468/sjAPKtporrJZCRbeanerwopnigga.ogg

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
e4533d7f133b66516daf77591e4875d8f24ba356b74a3d9fa2f882c5708798f8		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 7738 bytes

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