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

Static analysis result for SHA-256 137b982e52a32bb5…

MALICIOUS

Office (OOXML) / .XLSX

62.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: b20382ccf0ec90422aafcf79fa581ea6 SHA-1: 71d0008a854f107b825950decce20259b7edebee SHA-256: 137b982e52a32bb5d843be21236d3577f134ef4d06b21044815330827098581f
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The sample contains Excel 4.0 macros that are designed to execute a command. This command, 'mshta C:\ProgramData\fnsfunsfgrgnkjfsgnd.rtf', indicates that the macro attempts to download and execute a file from a remote URL. The extracted URLs point to Discord, likely hosting the second-stage payload. The use of XLM macros and the execution of an external file via mshta are strong indicators of a downloader or initial access mechanism.

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/909803598207131691/909841781959561286/ocaslmIpJheilhitler.mkv
    • https://cdn.discordapp.com/attachments/909803598207131691/909841485669740584/xpgFgnheilhitler.mkv
    • https://cdn.discordapp.com/attachments/909801430003638294/909839709780471898/XedYdknteTqauheilhitler.mkv

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
a0fb88b2d4dce02b60d1988fd11562784b360a831cf5ef2ed68becf4fc2cd6c8		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 4494 bytes

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