Office (OOXML) / .XLSX malware analysis — malicious · bf08b14672c3f515

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 5e772f7dd15753c43036c15a74d24eac SHA-1: b18124bc9c14490c854bab7ab278436daab4b02f SHA-256: bf08b14672c3f515b0623808a5402b257e76a93faef16be0d8c1fc1c6a47467b

182 Risk Score

Malware Insights

MITRE ATT&CK

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

The file contains Excel 4.0 macros, which are known to be used for malicious purposes. The macros utilize WinAPI functions such as URLDownloadToFileA and ShellExecuteA to download a second-stage payload from the URL https://absolutefitnessgym.com/ds/3.gif and execute it. This indicates a downloader or droppper attack pattern.

Heuristics 4

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.
URL reconstructed from XLM cell array (1 URL) critical OOXML_XLM_CELL_ARRAY_URL

Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell) or inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation. The reconstructed URL is invisible to literal-bytes URL extraction because it is never contiguous in the workbook stream. URLs were recovered by walking the BIFF12 record stream of every worksheet and macrosheet part and decoding RK/inline-string cells in both row-major and column-major order.
Embedded URL info EMBEDDED_URL

One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.

URL https://absolutefitnessgym.com/ds/3.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `33b39070cf703fb8920ce299136e91bbc3d2e0dae01e819c4b64ba4e4c896109`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	200463 bytes

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