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

Static analysis result for SHA-256 84aac3d5194fcf60…

MALICIOUS

Office (OOXML) / .XLSM

200.7 KB Created: 2021-09-13 09:41:09 UTC Authoring application: Microsoft Excel 12.0000
MD5: 8694d363cdc926109266f41758663c28 SHA-1: 2dfc06e6e815cf9e18085d043b13b5d9bdf44eaa SHA-256: 84aac3d5194fcf601596af4385093ff5bf3d1fd6ece335f53b8e0a785c156ccf
190 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, specifically using dangerous functions like FOPEN, FWRITE, FCLOSE, and EXEC. These functions are used to write data to a file and then execute it, likely a second-stage payload. The HALT() function is called at the end, indicating the completion of the macro's execution.

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
b0e9efa8281bd88f23deb4a06863ab585868826aad3adcc680af31ae9c2a187d		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1479 bytes

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