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

Static analysis result for SHA-256 b76183bea46e2642…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: d8dd800ee60fe58a7abf9c5fdc9dabc8 SHA-1: 7eabc6715cb4faf8817605ba12add867cdab33ea SHA-256: b76183bea46e26423fac80c8147c78f01b684e7ee1cf4a8bc55d6d8ab88b51b1
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic 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 such as URLDownloadToFileA and ShellExecuteA, suggesting the macro attempts to download and execute a secondary payload. The specific strings like 'URLDownloadToFileA', 'DownloadToFileA', 'ShellExecuteA', 'CreateDirectoryA', 'URLMon', and 'Kernel32' are directly indicative of this behavior. No specific family could be identified, but the technique is common for initial stage malware delivery.

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