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

Static analysis result for SHA-256 308256592edd6256…

MALICIOUS

Office (OOXML) / .XLSM

10.3 KB Created: 2021-09-20 19:36:11 UTC Authoring application: Microsoft Excel 16.0300
MD5: 541b3a0ea68a6568c7bb5d8546dfdf4d SHA-1: d7e9b417abccd380cb79736e39a72eccb6d4fbd5 SHA-256: 308256592edd625650e92e1515d297b16df8664252e1407cc950b77f575c79db
130 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1105 Ingress Tool Transfer T1547.001 Registry Run Keys / Startup Folder

The sample is an XLSM file containing Excel 4.0 macros. These macros utilize dangerous functions like FOPEN, FCLOSE, and HALT to write a VBScript payload to the startup folder, specifically at 'C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup\windows.vbs'. The script is designed to download and execute a second-stage payload. The use of these functions and the creation of a startup script indicate a downloader or droppper functionality.

Heuristics 4

  • 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: FOPEN, FCLOSE, 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
    • 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 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
2b479ad020dfecb129c889529d60a98e31ad4e831cfc10ccc6383890cd862c18		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5198 bytes

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