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

Static analysis result for SHA-256 1bcd56c71bb2e36f…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: 21dc9499c1066133979d7bd7158db0c5 SHA-1: dc4df5a3f74c0769c91d095428060c9c4d06fccc SHA-256: 1bcd56c71bb2e36f0f3d99a863a9a70a64860758b5cb4c7cdc07c391119bcf3b
120 Risk Score

Malware Insights

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

The file contains a critical Excel 4.0 macro sheet, identified by the OOXML_XLM_MACROSHEET heuristic. This macro sheet includes strings indicative of WinAPI calls for downloading and executing files, such as URLDownloadToFileA, DownloadToFileA, and ShellExecuteA. The presence of these WinAPI strings strongly suggests the macro's intent is to download and execute a second-stage payload from a remote source, aligning with common malware delivery techniques.

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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