Office (OOXML) / .XLSX malware analysis — malicious · 41341c4dabfa148a

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 12b6133adab1041737f0c33c999d2a71 SHA-1: 30790bb9e902bd13fb893e924a0c22cb6743d796 SHA-256: 41341c4dabfa148a8d6312a6624e1c93ad206be313e6674e782f22a68d692b86

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications T1204.002 Malicious File T1105 Ingress Tool Transfer

The sample is an Excel 4.0 macro sheet that contains WinAPI strings related to downloading and executing files, such as URLDownloadToFileA and ShellExecuteA. This indicates the macro's intent is to download and run a second-stage payload from a remote location. The presence of these WinAPI calls strongly suggests a malicious downloader functionality.

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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