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

Static analysis result for SHA-256 7e255ea9492add6d…

MALICIOUS

Office (OOXML) / .XLSX

75.1 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 4294c04117384c8a2068bb885b770a46 SHA-1: a896982484ef57e83685bb96bb6fdb3aa3bdaaab SHA-256: 7e255ea9492add6da3745e2798c002050bc0ba6258005f708d5e62114d543337
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, when executed, reconstruct and run the command 'wmic process call create 'mshta C:\ProgramData\excel.rtf''. This command is designed to download and execute a second-stage payload from one of the embedded URLs. The macros also contain references to three Discord URLs, which are likely hosting the malicious 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), inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation, or split across multi-char fragment cells a download formula concatenates by reference (=A1&A2&… / CONCATENATE(...)). 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/shared-string cells in row-major and column-major order plus FORMULA cell-reference concatenation in token 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/907666907405099111/907967144812220496/ZLDtPICf.mov
    • https://cdn.discordapp.com/attachments/907665395815677994/907970481230061678/srzdIGwxtBARWF.mov
    • https://cdn.discordapp.com/attachments/907666907405099111/907967425910300702/jWIcUr.mov

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
b540ba18a09139c1219189f2ded8439aaaf6f3fa9bf1abdb1a1aad6501caff81		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 161171 bytes

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