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

Static analysis result for SHA-256 aecd582263d363d3…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: f7150d9c1c06cb3c1d5bfdcd27e17a34 SHA-1: fa74a99a979f239c82ec6ab6a3b3f027509b6016 SHA-256: aecd582263d363d34107f2e3d8f68f866d865c8be8a79e62f5a6c1e4fb9f89f4
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The file is an Excel 4.0 macro sheet, which is a critical finding. Heuristics indicate the presence of WinAPI and download strings, specifically mentioning URLDownloadToFileA, DownloadToFileA, 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 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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