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

Static analysis result for SHA-256 8bda4a855c5342a7…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: 3f3e8480fb76c6b7cb7c9938f57f4e60 SHA-1: eee3dcdc4e4fb4ee80604350c355f430fc364a76 SHA-256: 8bda4a855c5342a7bd82e14d673efeb8864e1cc64f4cacb71ee186f36a2016eb
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Service Execution: Service Execution T1204.002 Malicious File: User Execution T1105 Ingress Tool Transfer

The sample contains critical heuristic firings indicating the presence of Excel 4.0 macros that utilize WinAPI functions for downloading and executing files. Specifically, the macros appear to use functions like URLDownloadToFileA and ShellExecuteA, suggesting an intent to download and run a second-stage payload. The file is an Excel 4.0 macro sheet, which is a common delivery mechanism for initial compromise.

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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