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

Static analysis result for SHA-256 b51386bb4d2d4032…

MALICIOUS

Office (OOXML) / .XLSM

38.7 KB Created: 2015-06-05 18:19:34 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-03-18
MD5: af3a81df3cf3bc0e78394fd8ef647fb1 SHA-1: 448c992b04c4a09dee7b6c27dfb311769339cea5 SHA-256: b51386bb4d2d4032b818368b974505f207936ff263c0c46aeb93a1a34eb51ea5
250 Risk Score

Malware Insights

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

The sample is an XLSM file containing Excel 4.0 macros, indicated by the 'OOXML_XLM_MACROSHEET' and 'OOXML_XLM_AUTOOPEN_DEFINEDNAME' heuristics. The 'OOXML_XLM_DANGEROUS_FN' heuristic confirms the use of dangerous XLM functions like FORMULA, which are used to download and execute payloads. The reconstructed URL 'http://amautatravel.com/cgi-bin/WhWIic/' and the command 'regsvr32.exe SysWow64\Windows\wnru' are indicative of a downloader attempting to fetch and run a second-stage payload. The file is flagged as malicious by ClamAV.

Heuristics 6

  • Excel 4.0 macro sheet (2 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: FORMULA 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.
  • ClamAV: Win.Malware.Agent-9993771-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Win.Malware.Agent-9993771-0
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 5 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
    • http://schemas.openxmlformats.org/markup-compatibility/2006
    • http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac
    • http://schemas.microsoft.com/office/spreadsheetml/2014/revision
    • http://schemas.microsoft.com/office/spreadsheetml/2015/revision2
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision3
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision6

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
a0c0f3e40bb0bcb71f69feab4a546d6971a6ad22d842de019237e043f0081a43		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1772 bytes
xlm_sheet_01.xml
2f8447d752b9aa82298eff83e8f17bd62a63f1ba62e6405681193f1dc7729f67		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/intlsheet1.xml 4474 bytes

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