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

Static analysis result for SHA-256 5c182db0b543316f…

MALICIOUS

Office (OOXML) / .XLSX

26.3 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: cc1f1dd14f9b84352560855c439b978b SHA-1: 216d2454a2fc6fdbdd26c8b4b3397642b9de4c18 SHA-256: 5c182db0b543316fbb0e3544a77fab4a620e037fb61d84d7d2ae2779bb7f93ce
242 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

The sample is an Excel file containing Excel 4.0 macros, which is a critical finding. These macros are designed to reassemble a payload from CHAR() and split formulas, ultimately downloading and executing a second-stage payload from the URL http://puroraw.com/. The macros also contain strings indicative of WinAPI calls like URLDownloadToFileA and ShellExecuteA, further supporting the payload download and execution behavior.

Heuristics 5

  • 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.
  • Binary XLM macro sheet with WinAPI/download strings critical OOXML_XLM_BINARY_WINAPI_STRINGS
    Excel 4.0 macro sheet is stored as BIFF12/XLSB binary data and contains Win32 download or process-execution API strings such as URLDownloadToFileA, ShellExecuteA, or CreateDirectoryA. These strings are high-signal in XLM macro sheets and catch payload-download macros that XML-formula scanners cannot parse.
  • 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) 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 http://puroraw.com/
    • http://puroraw.com/ds/3.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
bcb2a00478b552ea7aa0ba3395a02a282bd76772458f85092b2d3253d326ab01		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 200414 bytes

Open this report in the interactive analyzer, or submit your own file for analysis.