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

Static analysis result for SHA-256 17de988ebd2b722d…

MALICIOUS

Office (OOXML) / .XLSM

326.5 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: b1532f02c07d41ead7e4ef0fc4c0b11a SHA-1: 42795d998f06285a9223b34b7885c5da8e2af2d0 SHA-256: 17de988ebd2b722db226a5baed81ae44d7d8c6cf170e4fc1463b1d172375199d
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1566.001 Spearphishing Attachment

This Excel 4.0 macro-enabled document (XLSM) contains critical heuristics indicating the use of dangerous XLM functions like FOPEN, FWRITE, FCLOSE, EXEC, and HALT. The macro sheet defines a path, 'C:\ProgramData\nsxAnhRuDp.sct', which is likely where a second-stage payload will be downloaded and executed. The presence of an Auto_Open defined name and a hidden sheet further supports the malicious intent of executing arbitrary code.

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
fa6ec941f15c4393770a430c1bd90951d04e22f67bf8ee5ff3e72d3c5409cb38		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1639316 bytes

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