Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 03aa6c439ac9cd90…

MALICIOUS

Office (OOXML) / .XLSX

374.6 KB Created: 2020-05-11 14:19:29 UTC Authoring application: Microsoft Excel 15.0300
MD5: 02ffe47e375460da5fe4af01f85cad03 SHA-1: 9d15e8a3cec19e15482ff38f21a03fe67612c76e SHA-256: 03aa6c439ac9cd90c5eebebd9082c131fc48c4abf961260f51e328a70f196896
242 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

This Excel file contains critical Excel 4.0 macros and VBA code. The Workbook_Open macro displays a fake error message to the user. The XLM macros contain strings for WinAPI functions like URLDownloadToFileA, DownloadToFileA, and ShellExecuteA, indicating an intent to download and execute a second-stage payload. The reconstructed URL http://etlapgyartas.hu/0510.gif is likely the source of this payload.

Heuristics 6

  • 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.
  • Workbook_Open macro high OLE_VBA_WBOPEN
    Workbook_Open macro
  • VBA project inside OOXML medium OOXML_VBA
    Document contains a VBA project — VBA macros present
  • 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://etlapgyartas.hu/0510.gif
    • http://ns.adobe.com/xap/1.0/
    • http://www.w3.org/1999/02/22-rdf-syntax-ns#
    • http://ns.adobe.com/photoshop/1.0/
    • http://purl.org/dc/elements/1.1/
    • http://ns.adobe.com/xap/1.0/mm/
    • http://ns.adobe.com/xap/1.0/sType/ResourceEvent#
    • http://ns.adobe.com/xap/1.0/sType/ResourceRef#

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
708523a4aefd7042aef53a83e479a171b8f00706477822527e5e1fc9ec3a71c7		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 6253 bytes
vbaProject_00.bin
e6167f1529b14e2188eac2366772e7a05644f284513378266830479e3707d819		 vba-project OOXML VBA project: xl/vbaProject.bin 40960 bytes
xlm_sheet_00.bin
4497e29d351434919a69e185c8d56b847e0be01cfe213cb1e41e1cfb9a68b8f8		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 44173 bytes

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