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

Static analysis result for SHA-256 86f672f6e8d604d0…

MALICIOUS

Office (OOXML) / .XLSX

155.8 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300
MD5: f2387e25f2e1a33caa550034e443673f SHA-1: 4dd0cc843ccd2518ac2ce2a6268b06dd9c9a50f2 SHA-256: 86f672f6e8d604d0af61b015115542114e57d9db719969341101056d69a0eb60
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic

The file contains Excel 4.0 macros, which are known to be used for malicious purposes. These macros are designed to download and execute a second-stage payload from one of the two provided URLs. The XLM_REASSEMBLED_PAYLOAD and XLM_CELL_ARRAY_URL heuristics confirm the presence of these malicious macros and the extracted URLs.

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 (2 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://tattoo-thailand.com/cvAMN0orV9b/moon.html
    • https://roadtopassiveincomeonline.com/5lsYNUOzniG/moon.html

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
ac962eda506b15525c1cccc4208594d06a0effd902f1baf93d026be218f31732		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.bin 114843 bytes

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