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

Static analysis result for SHA-256 2aae13b899d4d270…

MALICIOUS

Office (OOXML) / .XLSM

247.6 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: eaac64f0338732ec1e4764fb2aef85dc SHA-1: 4560f8ac6ea2843dd5926232012b0713117c88c7 SHA-256: 2aae13b899d4d2707ffdd0fea10f1c1208aba809d118a4b32a94b4af238bc3a2
190 Risk Score

Malware Insights

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

The sample is an XLSM file containing Excel 4.0 macros. The macros utilize dangerous functions like FOPEN, FWRITE, and FCLOSE to write a script file to disk at 'C:\ProgramData\TelrglZwd.sct'. The script is constructed using character codes, which are then concatenated to form the final path. This indicates the macro's intent is to download and execute a second-stage payload.

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
a07afd1ed31bba79f2105d3edb79d1db4a7e099315ceb7fce77521272a80733c		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 702370 bytes

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