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

Static analysis result for SHA-256 0fc36de9d9dc726f…

MALICIOUS

Office (OOXML) / .XLSM

77.4 KB Created: 2021-02-08 12:04:31 UTC Authoring application: 16.0300
MD5: 331d0154abc52d891022866228f0fd7d SHA-1: efb6d8aa2208c3e146f7d5aec7a36e74e933a5ae SHA-256: 0fc36de9d9dc726f53fd9849e8006869e5691df817c3bde191d68e14f7580dd4
210 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1203 Exploitation for Client Execution T1105 Ingress Tool Transfer

The sample is an XLSM file containing Excel 4.0 macros. Heuristics indicate the use of dangerous XLM functions like RETURN, which are often used to download and execute payloads. The VBA code also explicitly calls URLDownloadToFileA, a function used to download files from URLs. This suggests the macro is designed to fetch and run a second-stage payload.

Heuristics 6

  • URLDownloadToFile in VBA critical OLE_VBA_DOWNLOAD
    URLDownloadToFile in VBA
  • 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: 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.
  • VBA project inside OOXML medium OOXML_VBA
    Document contains a VBA project — VBA macros present
  • Hidden worksheet (hidden) low OOXML_HIDDEN_SHEET
    Excel workbook contains 3 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

Extracted artifacts 3

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
8a5b3606cd9bcfa97abb4fd3ef11b50b15f4c7229443bc158dee06d3aba6ffbd		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 3690 bytes
vbaProject_00.bin
2f8bb105a638bf915ad4d035dd9df54df9b24f9de4f495f2c97f740082bcf060		 vba-project OOXML VBA project: xl/vbaProject.bin 22528 bytes
xlm_sheet_00.xml
b9e7d2fd302a507b07af7b2853e249f073297a134f17cd3332edeccea2b14c77		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 910 bytes

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