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

Static analysis result for SHA-256 370258df641d0688…

MALICIOUS

Office (OOXML) / .XLSX

133.0 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: e5ca86bd5080d9c93e5cc392fa5498b8 SHA-1: 53af11a5242edddc6b4328669bfc679463aea14d SHA-256: 370258df641d0688aba764d7812bc26270c46612966516342b1ebc03e390888f
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1059.001 PowerShell

The sample is an Excel file containing Excel 4.0 macros, indicated by the OOXML_XLM_MACROSHEET heuristic. The presence of the Auto_Open defined name and dangerous XLM functions like CALL, EXEC, and RETURN (as seen in the OOXML_XLM_DANGEROUS_FN heuristic) strongly suggests that the macros are designed to execute arbitrary code. The ALERT function, when deobfuscated, reveals a string that appears to be an error message, but the underlying mechanism is capable of executing commands. This points to a downloader or initial execution stage for a more complex attack. No specific family could be identified.

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
c6699f0ef4a2f93dbce6175c506535a37bf9813fa014c888e25e72a3ce0ccd0d		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5205 bytes

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