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

Static analysis result for SHA-256 265cc3db46cf8eb8…

MALICIOUS

Office (OOXML) / .XLSX

9.2 KB Created: 2022-06-28 13:43:35 UTC Authoring application: Microsoft Excel 16.0300 First seen: 2022-08-03
MD5: dbad54d41f4e3bb1341cac986a38c62d SHA-1: 456fc6db8ab3478de935475c74a262499cf10da6 SHA-256: 265cc3db46cf8eb851a423f975ca0b0238dc283949a544a69f96a0c09b5a658d
182 Risk Score

Malware Insights

MITRE ATT&CK
T1204.002 Malicious File: User Execution T1059.005 Command and Scripting Interpreter: Visual Basic T1105 Ingress Tool Transfer

The sample contains Excel 4.0 macros that utilize dangerous functions like EXEC and HALT. The EXEC function is used to download a file named 'nc.exe' from the IP address 78.85.17.88 to the C:\Windows\Tasks\ directory using curl. The HALT function is then called, likely to terminate the macro execution after the download. This indicates a downloader functionality aiming to execute a second-stage payload.

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.
  • 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: 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.
  • 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://78.85.17.88:8054/nc.exe
    • 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
64b01ea9afd2a4786364fd80da4001c6ecf36be2c499347b33db3fbae9c31118		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1451 bytes

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