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

Static analysis result for SHA-256 1a30a959963f1784…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: a1e5a7d7a2a79c9ea90a9e9e69ca8ec3 SHA-1: 298d87db11e8fd675abb219680c1d53fd2669da8 SHA-256: 1a30a959963f17843aec2901ea7c375652edc59c041139c128cae195a5377bc2
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 4.0 macro sheet, identified by the OOXML_XLM_MACROSHEET heuristic. The OOXML_XLM_BINARY_WINAPI_STRINGS heuristic indicates the presence of WinAPI calls such as URLDownloadToFileA, DownloadToFileA, ShellExecuteA, and CreateDirectoryA, along with references to URLMon and Kernel32. This strongly suggests the macro is designed to download and execute a second-stage payload from a remote source. The specific URL and executable path are not fully reconstructed due to truncation, but the intent is clear.

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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