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

Static analysis result for SHA-256 272b44c28939e6a4…

MALICIOUS

Office (OOXML) / .XLSX

10.2 KB Created: 2021-09-16 19:14:17 UTC Authoring application: Microsoft Excel 16.0300
MD5: 0f4d1bf99c1d9cbc3cfbb98e5c6d9730 SHA-1: 93bf4b6cb3253fad1e3ee4388c190b93e34743e5 SHA-256: 272b44c28939e6a4b5e9d6280fde5c2d70568b1363ae288595e71eae6a146cb8
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

This malicious Excel 4.0 macro sheet utilizes dangerous functions like FOPEN, FCLOSE, and CALL to construct and write a VBScript file named 'windows.vbs' to the user's startup folder. The script is intended to download and execute a second-stage payload, establishing persistence. The use of these specific XLM functions and the startup folder placement are strong indicators of a downloader malware.

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
0801295603af3fb0a3a32e2d81ce729046093593f01d27d7499bded7e831f650		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5198 bytes

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