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

Static analysis result for SHA-256 99d758810a0c8c39…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: bb8f8ce6dd2eaef4e0e9ba1676e6c481 SHA-1: f9ad5f65bc33f8594a14cfe769d903a90b90bc16 SHA-256: 99d758810a0c8c3983aa75d3a904fada5f6485eda36a8f3c0f7a58f59eac7bcb
120 Risk Score

Malware Insights

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

The file is an Excel spreadsheet containing Excel 4.0 macros. 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 second-stage payload from a remote location. The presence of these WinAPI calls and the nature of the macro sheet strongly indicate a malicious intent to compromise the user's system.

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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