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

Static analysis result for SHA-256 597937827f256a0e…

MALICIOUS

Office (OLE) / .XLSX

36.0 KB Created: 2020-11-25 10:44:48 Authoring application: Microsoft Excel
MD5: 6d1fd4cdb9f6644824b0f7e9e5100df7 SHA-1: 50fc7e2f6b193f8fdb2db5b1e8cabb1f0b10e1c2 SHA-256: 597937827f256a0eed431edaf24dc7f83d3ee6ab83006f27b807323e7e5ff91a
140 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1566.001 Spearphishing Attachment

The file contains Excel 4.0 macros, specifically an Auto_Open function, which is a known technique for executing malicious code upon opening the document. The critical heuristic firings indicate the presence of dangerous formula APIs within the Auto_Open macro, suggesting it's designed to run arbitrary commands. The macro sheet itself is named 'ZefokFM', which might be a campaign indicator.

Heuristics 3

  • Excel 4.0 Auto_Open defined name critical OLE_XLM_AUTOOPEN_DEFINEDNAME
    oletools recovered an Auto_Open / Auto_Close entry from an Excel 4.0 macro sheet. The raw BIFF name can be tokenized or partially opaque to byte-string checks, but the recovered macro listing confirms the workbook has an XLM auto-execution entry.
  • XLM Auto_Open with dangerous formula APIs critical OLE_XLM_DANGEROUS_FN
    Excel 4.0 macro sheet contains an Auto_Open / Auto_Close entry and dangerous XLM formula APIs that can invoke programs, write files, or transfer control without VBA.
  • Excel 4.0 (XLM) macro sheet present medium OLE_XLM_AUTOOPEN
    Workbook contains an Excel 4.0 macro sheet sub-stream — XLM is rarely seen in modern legitimate workbooks and was a major Office malware vector during 2020-2022.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_macros.txt
b3d505901c8f79f26c8b323fc066da28f8c32f0c01b8f7047da0a17de84e1b03		 xlm-macro oletools.olevba.extract_all_macros (XLM macro listing) 6432 bytes

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