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

Static analysis result for SHA-256 d96e4dffd81af9d3…

MALICIOUS

Office (OOXML) / .XLSM

267.7 KB Created: 2021-09-13 09:41:09 UTC Authoring application: Microsoft Excel 12.0000
MD5: 6cf087b90352ece06bc1170c5f936830 SHA-1: c47047cbb8d8cd301212f450f65fbb65f66a6842 SHA-256: d96e4dffd81af9d30dbac0984b5bbfe829d593b12396eca61fb5500c80c91c46
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 XLSM 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, FWRITE, EXEC, and HALT to download and execute a payload. Specifically, the FOPEN function is used to open a file, FWRITE to write data to it, and EXEC to run it. The 'OOXML_XLM_DANGEROUS_FN' heuristic confirms the use of these potentially malicious API calls. The presence of a hidden sheet ('OOXML_HIDDEN_SHEET') further suggests an attempt to conceal malicious activity.

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, FCLOSE, EXEC, HALT 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
700bd695b0a18f493e407d2b62f3bc0f731f50896fe2a908fecc7c4450364889		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1486 bytes

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