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

Static analysis result for SHA-256 df90a5e7f9fb8b6b…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: f68c05f114d1cd8d51663b476795c04a SHA-1: 3ff433ae8ac8c7b82ce36254fd3866de10dd6a0e SHA-256: df90a5e7f9fb8b6b1e34f3d7af0a817bc2e9ec567392af778b272644914bc444
120 Risk Score

Malware Insights

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

The critical heuristic firings indicate the presence of binary Excel 4.0 macros within an OOXML file. These macros contain strings related to WinAPI functions such as URLDownloadToFileA, DownloadToFileA, ShellExecuteA, and CreateDirectoryA, strongly suggesting the file's purpose is to download and execute a secondary payload. The presence of these WinAPI calls and the nature of the heuristics lead to a high confidence assessment of this attack pattern.

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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