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

Static analysis result for SHA-256 aa8bca143d609653…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: a4f38313ce3a7251d9f2d887397c549c SHA-1: becf6450c39cf5ab08dc36cb9a9b21caa9e223dc SHA-256: aa8bca143d609653a305a1e32e623a62115fe0734b2e5502405f8511d1ea71ee
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 4.0 macro-enabled spreadsheet. Critical heuristics indicate the presence of WinAPI and download strings within the macro sheet, specifically mentioning URLDownloadToFileA, DownloadToFileA, ShellExecuteA, and CreateDirectoryA. This strongly suggests the macro's intent is to download and execute a second-stage payload from a remote location, likely to a specified .exe path. The file is therefore classified as a downloader.

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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