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

Static analysis result for SHA-256 76e84f95544f022b…

MALICIOUS

Office (OOXML) / .XLSX

132.3 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 6ea483c95887a7c4b6807ac9480139ee SHA-1: 4c59442cf388dd55310ea6a25e8eb08e3e220c56 SHA-256: 76e84f95544f022babce522480d717df069ce42032783faf63490973fd9d5376
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution

The file contains Excel 4.0 macros, specifically using the `FOPEN`, `FWRITE`, `EXEC`, and `RETURN` functions, which are indicative of malicious activity. The macros appear to be constructing a path to download and execute a second-stage payload. The reconstructed path is `C:\ProgramData\JalWsSnnoC\tf nuc`.

Heuristics 5

  • 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.
  • Excel 4.0 Auto_Open defined name critical OOXML_XLM_AUTOOPEN_DEFINEDNAME
    Workbook defines _xlnm.Auto_Open or _xlnm.Auto_Close while containing an XLM macro sheet. This is the OOXML/XLSB auto-execution shape for Excel 4.0 macros.
  • Dangerous XLM formula APIs: FOPEN, FWRITE, EXEC, RETURN critical OOXML_XLM_DANGEROUS_FN
    Excel 4.0 macro sheet uses formula APIs that call directly into Win32 (=CALL/=EXEC/=REGISTER/=FORMULA). These are the primitives used to download payloads, write files, and start processes from an XLM macro without invoking VBA.
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 1 hidden sheet(s) — hidden sheets are commonly used to conceal macro code, staging data, or intermediate payload construction
  • 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://schemas.openxmlformats.org/spreadsheetml/2006/main
    • http://schemas.microsoft.com/office/excel/2006/main
    • http://schemas.openxmlformats.org/officeDocument/2006/relationships

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
317ec1a7060b9c29030dfa9e2d5a05c6b47d2a070fc8d042cb294a5bc7b1afa2		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 4946 bytes

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