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

Static analysis result for SHA-256 cf636c62369a3e2e…

MALICIOUS

Office (OOXML) / .XLSM

272.1 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 054a63b8e3d051b989f7b74a6759c11d SHA-1: f5df5c8839f3f4ac1af1ef22132225e2e580c5de SHA-256: cf636c62369a3e2eca769ae4ab012647fd05f7639f98d163fc203373d19dbe2d
190 Risk Score

Malware Insights

MITRE ATT&CK
T1204.002 Malicious File: User Execution: Malicious File T1059.005 Command and Scripting Interpreter: Visual Basic T1218.011 System Binary Proxy Execution: Rundll32

This XLSM file contains Excel 4.0 macros, which are known to be used for malicious purposes. The macros utilize dangerous functions like FOPEN, FWRITE, FCLOSE, and EXEC to write and execute a script. Specifically, the macro constructs the path 'C:\ProgramData\XXeUti.sct' and then uses the EXEC function to run it via 'rundll32.exe C:\ProgramData\XXeUti.sct,DllRegisterServer'. This indicates the file's primary function is to download and execute a second-stage payload.

Heuristics 5

  • 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.
  • Excel 4.0 Auto_Open defined name critical OOXML_XLM_AUTOOPEN_DEFINEDNAME
    Workbook defines _xlnm.Auto_Open or _xlnm.Auto_Close while containing an XLM macro sheet. This is the OOXML/XLSB auto-execution shape for Excel 4.0 macros.
  • Dangerous XLM formula APIs: FOPEN, FWRITE, FCLOSE, EXEC, 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

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
b79f37cf8edfedc0e3ec7252dfb010d7100e8345872c8abf9f72a60f8804a88f		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 890147 bytes

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