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

Static analysis result for SHA-256 53c9fcabdc30f2bf…

MALICIOUS

Office (OOXML) / .XLSM

34.2 KB Created: 2021-01-19 08:51:14 UTC Authoring application: 16.0300
MD5: bfbef75d3bad76c3aa3aa3ddcc4b2e37 SHA-1: 7af38eb27730ef11e2407f1eb7bc5053f0e6f6d5 SHA-256: 53c9fcabdc30f2bf24bc0c3a8586de2986417b3e51d697530c8a84a7cea37f79
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic for Applications T1059.001 PowerShell T1204.002 Malicious File

This XLSM file contains Excel 4.0 macros, indicated by the critical heuristic firings for 'OOXML_XLM_MACROSHEET' and 'OOXML_XLM_DANGEROUS_FN'. The presence of the 'RETURN()' function in the macrosheet suggests an attempt to execute arbitrary code, likely for downloading and executing a secondary payload. The VBA code, while partially obfuscated, also contains functions that appear to be related to random number generation and array manipulation, which could be used in payload staging or obfuscation. No direct IOCs such as URLs or file hashes were extracted, but the technique itself is highly indicative of a downloader or initial access stage.

Heuristics 6

  • 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.
  • Dangerous XLM formula APIs: 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.
  • Auto_Open macro high OLE_VBA_AUTO
    Auto_Open macro
  • VBA project inside OOXML medium OOXML_VBA
    Document contains vbaProject.bin — VBA macros present
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 2 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

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
1b70075c55e6cce9aa17d3012fcce1d981fdfb2a4708bd4df1e571205736c985		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 4481 bytes
vbaProject_00.bin
2ddc58478f7b917f40ea1f063b28c5b9f6945b9e4e5fa8469fc732d73bf674f6		 vba-project OOXML VBA project: xl/vbaProject.bin 29696 bytes
xlm_sheet_00.xml
5b5dcb2f030adcab65a6222035f9e1adf076e7494a34f1fe990be2faa35a9a03		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1103 bytes

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