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

Static analysis result for SHA-256 5df67b5d2ce0f04d…

MALICIOUS

Office (OOXML) / .XLSX

83.2 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: d3dec46781b6ae14334473410ca6865a SHA-1: cf3e90910f11ab5a9aef75fdc37864cc87b9ff5e SHA-256: 5df67b5d2ce0f04d77090f25ed504c306583cd00e4d4fbef8b7c461818919486
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 reassemble a command to execute mshta.exe, which in turn is instructed to download and run a payload from a specified RTF file. The macros also contain URLs that are likely used to host the second-stage payload. The execution of mshta.exe with a downloaded file indicates an attempt to download and execute a further stage of 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/910212171147915317/910551139429257216/vHjoZOlUDniggerjewhitler.mp4
    • https://cdn.discordapp.com/attachments/910212171147915317/910551112715747348/EnbnZedVJNkoniggerjewhitler.mp4
    • https://cdn.discordapp.com/attachments/910212171147915317/910550457825501204/UWJYJCniggerjewhitler.mp4

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
97dbde4d2cfaf99c517f800c556d86a178dc50ffb3ed80b0796ac32c5db40d44		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 3376 bytes

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