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

Static analysis result for SHA-256 8518695008ce458c…

MALICIOUS

Office (OOXML) / .XLSX

78.8 KB Created: 2021-03-16 13:14:06 UTC Authoring application: Microsoft Excel 16.0300
MD5: 9236b9c6aa22afd71b5309997ee95c85 SHA-1: d00013f2fd3178497f11cfd3ec5146ad24353d04 SHA-256: 8518695008ce458c1315c722966e4045224b2b5a579fb5c73cb8d73c78cafa83
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 are designed to download a DLL payload from 'http://sported.xyz/campo/g/gC' and save it to 'C:\ProgramData\flotsh\h4gf.dll'. The macros utilize functions like Kernel32CreateDirectory and UrlmonURLDownloadToFile, indicating an intent to establish a directory and download an executable. This suggests a downloader or droppper functionality.

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 (1 URL) 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 http://sported.xyz/campo/g/gC

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
7db73557b76b8e96e8ef10decfc2b3d132332eba18da2eac10b37c9903ad2230		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 2544 bytes

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