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

Static analysis result for SHA-256 dbe358bd92f4d97d…

MALICIOUS

Office (OOXML) / .XLSM

158.2 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 7b4c9957c8fe2262e09c00845ead7aa8 SHA-1: e8a2eae199f1a71d479b97463422e7bb8f2c6640 SHA-256: dbe358bd92f4d97dccc73e246360965cca7f1be23b998a232c3ea92021cee572
130 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1204.002 Malicious File T1105 Ingress Tool Transfer

The sample is an XLSM file containing Excel 4.0 macros. These macros utilize dangerous functions like FOPEN, FWRITE, and FCLOSE to write a VBScript file named 'NkMOWUp.vbs' to the 'C:\ProgramData\' directory. The script then uses 'Wscript.Shell' to execute this file, likely to download and run a second-stage payload. The use of hidden sheets and dangerous XLM functions indicates a malicious intent to conceal and execute arbitrary code.

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, FWRITE, FCLOSE, EXEC, RETURN 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
ec1491b45f3715caa41882fd7a91af12dbaaa81d7a90fbc792bb0d2180bd92d6		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5677 bytes

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