Office (OOXML) / .XLSX malware analysis — malicious · 21b6a7c8b372f187

MALICIOUS

Office (OOXML) / .XLSX

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

MD5: 6217a2834fab8e534ae6206522b01c6a SHA-1: 0f47071df9df754abdab33d2e6076268838a8266 SHA-256: 21b6a7c8b372f187223342ced4c5fce0e4392c1f40251dec71f05101fd2f1f55

182 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic for Applications 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 and execute a payload from the URL https://kacedu.in/ds/4.gif. 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://kacedu.in/ds/4.gif

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `4d3267d5cb48a24d8d5a76370a2eebaf0d0fae662a1ae41551cbc28e948767c7`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	197524 bytes

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