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

Static analysis result for SHA-256 b2c9c7b260cf8a69…

MALICIOUS

Office (OOXML) / .XLSM

10.2 KB Created: 2021-10-18 18:49:04 UTC Authoring application: Microsoft Excel 16.0300
MD5: f291104d747817316c0bab8f09844727 SHA-1: 7ebe6bace53395601dc4d1455757bd0054490221 SHA-256: b2c9c7b260cf8a691608faab56baee7f34c939bc3d7a183361212d446d5b8600
130 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1105 Ingress Tool Transfer T1547.001 Registry Run Keys / Startup Folder

The file contains Excel 4.0 macros, indicated by the 'OOXML_XLM_MACROSHEET' and 'OOXML_XLM_DANGEROUS_FN' heuristics. The macros utilize dangerous functions like FOPEN, FCLOSE, and HALT, which are used to directly call Win32 APIs. Specifically, the script reconstructs the path 'C:\Users\Public\Microsoft\Windows\Start Menu\Programs\Startup\windows.vbs' and writes to it using FOPEN and FWRITELN. This suggests the macro's intent is to download and execute a second-stage payload via a VBScript placed in the startup folder, establishing persistence.

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, FCLOSE, 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
    • http://schemas.openxmlformats.org/markup-compatibility/2006
    • http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac
    • http://schemas.microsoft.com/office/spreadsheetml/2014/revision
    • http://schemas.microsoft.com/office/spreadsheetml/2015/revision2
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision3
    • http://schemas.microsoft.com/office/spreadsheetml/2016/revision6

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
afed644ff61c1dafc8b788d0676d7a2d9196103f09585d50d692aa5adcfb00c2		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 5237 bytes

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