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

Static analysis result for SHA-256 7efd1141f6d4858c…

MALICIOUS

Office (OOXML) / .XLSM

143.9 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 2ac8e068af04acae7b07a376b1adcf57 SHA-1: 7034cd5a8fb78c201bfeae534c301029c2150bfe SHA-256: 7efd1141f6d4858cd381b53fabdb2906a0a23c1329dbae42327aeda63c934dfb
190 Risk Score

Malware Insights

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

The sample is an Excel 4.0 macro-enabled spreadsheet. The critical heuristics indicate the use of dangerous XLM functions like FOPEN, FWRITE, and EXEC, which are used to download and write files. The script explicitly uses FOPEN to write to 'C:\ProgramData\SK\Zbt.rtf', indicating a file download and staging operation. The ALERT function also suggests a user-facing lure, though the exact content is obfuscated.

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, 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
06f44f4851d1f864358b5d99a9e961422448ecdc0efadf6524eb33f0e6e249d2		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 4220 bytes

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