Office (OOXML) / .XLSX malware analysis — malicious · 6a237e3404ec7828

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300

MD5: 2a95828b3bf62635cec622b5e1db0c5e SHA-1: a15ed1c3b35e4abb0d8f63788307d0fe76baad8d SHA-256: 6a237e3404ec78283af9d99b717e9ee9da745ead55e141b9c5e87c19fccd479c

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1203 Exploitation for Client Execution

The sample contains Excel 4.0 macros, which are known to be used for malicious purposes. The heuristics indicate the presence of WinAPI and download strings, specifically mentioning functions like URLDownloadToFileA and ShellExecuteA. This suggests the macro is designed to download and execute a secondary payload, likely an executable file, from a remote source.

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.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `99a6a52acb8f5c734f6d86faf89e0637a94ac99f953aa583d2658b47d2e1f9b9`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	194023 bytes

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