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

Static analysis result for SHA-256 cfed7707ec0b03c4…

MALICIOUS

Office (OOXML) / .XLSX

131.0 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: e2b9c45d656fe41c2e7a572153aac7c3 SHA-1: a62f735cec096eb3d71333cd6404e3b104ddfa82 SHA-256: cfed7707ec0b03c4258047a7db7f5d0a1a181285efcff3ce9dbddbc98005bf51
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1059.001 PowerShell T1059.003 Windows Command Shell

The sample is an Excel file containing Excel 4.0 macros, indicated by the 'OOXML_XLM_MACROSHEET' and 'OOXML_XLM_AUTOOPEN_DEFINEDNAME' heuristics. The macros utilize dangerous functions like FOPEN and EXEC, which are capable of downloading and executing arbitrary code. The 'DOC BODY' section contains obfuscated JavaScript-like code that attempts to construct strings for a URL and potentially execute commands. The presence of these functions and the obfuscated script strongly suggest the macro is designed to download and run 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
dd565a71dbe2f8616d0131f03a37c79471b25e8c8383b7a5f14f2285cf571cc9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5755 bytes

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