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

Static analysis result for SHA-256 8742949a7f191d62…

MALICIOUS

Office (OOXML) / .XLSM

35.2 KB Created: 2021-01-25 14:03:43 UTC Authoring application: Microsoft Excel 16.0300
MD5: c0078fb2386460b8c5a980f70b9bcd26 SHA-1: 8384b6c60964e1a1dafd68f5e00a9d5f154e6e41 SHA-256: 8742949a7f191d62317a4aef581b93991af1c94b0f50de6b7fc61743c073ce9a
210 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution

This XLSM file contains Excel 4.0 macros that leverage the dangerous `RETURN()` function, which can call Win32 APIs. The `URLDownloadToFileA` function is explicitly referenced, indicating the macro's intent to download a second-stage payload from a remote source. The presence of hidden sheets and the use of `RETURN()` strongly suggest a downloader or droppper functionality.

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 a VBA project — 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
    • http://schemas.microsoft.com/office/spreadsheetml/2014/revision
    • http://schemas.microsoft.com/office/spreadsheetml/2015/revision2
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision3
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision6

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
04653d4f70c19dc08fd54c67134a1aa8916a983c36b98af1cea0988bbde9c11c		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 3487 bytes
vbaProject_00.bin
a289437d1357276aa7690bbd1c0cce0413c092c87a41d9960eed7625151ebd5b		 vba-project OOXML VBA project: xl/vbaProject.bin 23040 bytes
xlm_sheet_00.xml
f8b2a642d8ce45fed71ed8e7bb04a79f739211cd0786118a697844ca742c229f		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1350 bytes

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