Office (OOXML) / .XLSX malware analysis — malicious · 5cb8a159cf0ace0c

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 4ea5b0e604cc671e2ff5a0a39312486c SHA-1: b1552208268892996e47c9e2fde76697c6aa3948 SHA-256: 5cb8a159cf0ace0cb4df654cb197aadb3d1cc87f25ff9a3e42f37970bbac4dc0

120 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1105 Ingress Tool Transfer

The sample contains Excel 4.0 macros, identified by the OOXML_XLM_MACROSHEET heuristic. These macros include strings indicative of downloading and executing files, such as URLDownloadToFileA and ShellExecuteA. The OOXML_XLM_BINARY_WINAPI_STRINGS heuristic further confirms the presence of WinAPI calls and download-related strings, suggesting the macro's purpose is to fetch and run a secondary payload.

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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