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

Static analysis result for SHA-256 287bd7f7b56942e9…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: a4620e5f225c3368c114b3138273c647 SHA-1: cf82d63506088ef96c37555d30dbf759fbf9522c SHA-256: 287bd7f7b56942e9787271b2ba4b1bc7d1b58999f461b351734f3ff34fc5ec83
120 Risk Score

Malware Insights

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

The file contains an Excel 4.0 macro sheet, which is a critical finding. The heuristics indicate the presence of WinAPI calls such as URLDownloadToFileA, DownloadToFileA, and ShellExecuteA, suggesting the macro's purpose is to download and execute a secondary payload. The macro sheet itself is heavily truncated, preventing a full analysis of the download URL or the specific executable path, but the intent to download and run a file is clear.

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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