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

Static analysis result for SHA-256 df1d5c684c9e73e2…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: 9995c92fa7f2caf2af1ee19ac3ac8999 SHA-1: 9bb53c8b08be185388f102be3a516aa038d1eee9 SHA-256: df1d5c684c9e73e2d858c4b9eacf5f64c1c3b48c814c08a1e333b9f3b65ff36d
120 Risk Score

Malware Insights

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

The sample contains critical heuristic firings indicating it is an Excel 4.0 macro sheet with WinAPI and download strings. The embedded macro sheet uses functions like URLDownloadToFileA and ShellExecuteA, strongly suggesting it is designed to download and execute a second-stage payload from a remote location. The specific WinAPI calls and the nature of the macro sheet point to a downloader or droppper functionality.

Heuristics 2

  • 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.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
99a6a52acb8f5c734f6d86faf89e0637a94ac99f953aa583d2658b47d2e1f9b9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 194023 bytes

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