Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 81f7e9e50c5a3470…

MALICIOUS

Office (OOXML)

306.1 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 4d3e19a8d63bfc02cb9e892859649e5f SHA-1: 1bd59b9894eb205509b817bc60d019d8278d496d SHA-256: 81f7e9e50c5a3470e512aa7706d08f66ea827fbf231196eb363da247db5e558b
250 Risk Score

Malware Insights

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

The file contains critical heuristics indicating the presence of Excel 4.0 macros, including dangerous functions like FOPEN, FWRITE, FCLOSE, EXEC, and HALT. The macro code constructs a path to a script file, "C:\ProgramData\UbZhsPW.sct", and uses FOPEN to open it, suggesting it will be used to download and execute a second-stage payload. The ClamAV detection further confirms its malicious nature as a downloader.

Heuristics 6

  • 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.
  • ClamAV: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0
  • 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
7955e144213ad6fbd884c7de1bae02f6f46736b9ba2641fec0aa9b0cc7f3a2ce		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1626237 bytes

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