Office (OOXML) / .XLSX malware analysis — malicious · b1a75327034e884e

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 85da5c1e24b6ce04c874bd6065a36c82 SHA-1: 00061b6ea9b95553529b97ce7f2bdf7d2a2a607c SHA-256: b1a75327034e884ed1b442f36dfd493779f399a9d46aa87c77ba5a3448b8dcca

182 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic T1204.002 Malicious File

The sample is an Excel file containing Excel 4.0 macros, which is highly suspicious. The macros utilize WinAPI functions such as URLDownloadToFileA and ShellExecuteA to download and execute a secondary payload from the URL http://saeshoes.com/ds/4.gif. This indicates a downloader or droppper functionality.

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 http://saeshoes.com/ds/4.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `cf3f339bbd5d1e97a5315c960037677181f9a6d73d01ff7f62691aaf05cfc366`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	197532 bytes

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