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

Static analysis result for SHA-256 af975a75c61e34bf…

MALICIOUS

Office (OOXML) / .XLSM

35.4 KB Created: 2021-01-25 14:33:26 UTC Authoring application: 16.0300
MD5: d0c94cb71ebba770ba675c94ff3b7729 SHA-1: 4b3fca139948d977ad21576de881334e745362c9 SHA-256: af975a75c61e34bfe147221fc395b893d8306c93a8e80e17d43acddf2a4f1da0
210 Risk Score

Malware Insights

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

This XLSM file contains Excel 4.0 macros that leverage the `RETURN()` function, which can call Win32 APIs. The `URLDownloadToFileA` function is explicitly called, indicating the macro's intent to download a second-stage payload from a remote source. The presence of hidden worksheets and the use of dangerous XLM formula APIs further support this malicious intent. No specific family could be identified, but the technique is common for initial payload delivery.

Heuristics 6

  • URLDownloadToFile in VBA critical OLE_VBA_DOWNLOAD
    URLDownloadToFile in VBA
  • 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.
  • VBA project inside OOXML medium OOXML_VBA
    Document contains vbaProject.bin — VBA macros present
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 3 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
64dfadc60101187b9f5948f7a294f1172c191547775dbc349ae62bf540ed87ce		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 3632 bytes
vbaProject_00.bin
9354abc5565468c15d99ed11142762ec1ecda8b3d10ecc272369f41f540fcb0a		 vba-project OOXML VBA project: xl/vbaProject.bin 25088 bytes
xlm_sheet_00.xml
e7f433b9b6ff773d85557baf829f63d74cdd398afd824a77b694235dc76c1c2f		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 980 bytes

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