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

Static analysis result for SHA-256 ed8de48ab7c84638…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: efd4a523d6296988cdd83d2fd1b8413a SHA-1: 0dfc40e6e460e5cd5d3c6d86a06f2d87f096e691 SHA-256: ed8de48ab7c846382584b06247db4a5190ea1b325d542a8bf1b09d51c275a6ae
120 Risk Score

Malware Insights

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

The sample is an Excel file containing Excel 4.0 macros. Heuristics indicate the presence of WinAPI calls and download strings, specifically mentioning URLDownloadToFileA and ShellExecuteA. This suggests the macro is designed to download and execute a secondary payload, likely an executable file, from a remote source. The specific WinAPI functions and the nature of the macro sheet strongly point towards 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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