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

Static analysis result for SHA-256 30c938bcf64e0dae…

MALICIOUS

Office (OOXML) / .XLSX

140.6 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 20988d1d1e546b5ba58346e6f5aaa002 SHA-1: 23173e1237888874c1aa4fa6e1e4798ff2b54b65 SHA-256: 30c938bcf64e0dae4efde1256a34bdf2b92cd50b8f01e63013cf128fdc9eb4eb
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic, Visual Basic for Applications T1204.002 Malicious File T1059.001 PowerShell T1105 Ingress Tool Transfer

This Excel 4.0 macro-enabled workbook contains a hidden sheet with macros that utilize dangerous functions like FOPEN and ALERT. The FOPEN function is used to write to a file named 'tCQrlzW.rtf' in the ProgramData directory, indicating a likely download and execution chain. The ALERT function constructs a message string, 'Error! Sending report to Microsoft..', which is likely a lure to disguise the malicious activity. The presence of these functions and the file path strongly suggest the sample is a downloader for a second-stage payload.

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
0266bb41988d4e7459db28fe78e1446777aacecc201d81a972c2adea2de42cc2		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5021 bytes

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