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

Static analysis result for SHA-256 e5cc7cb98d24d118…

MALICIOUS

Office (OOXML) / .XLSM

46.1 KB Created: 2020-12-07 11:26:30 UTC Authoring application: 16.0300
MD5: e057f629d3598d9a1d17bd32959cdd87 SHA-1: 0c5a833d917b1587a99c2fc9c6eea864b504febb SHA-256: e5cc7cb98d24d1186af5bd54de2c0ad8ff9ab2e18b2eac426ea00de7b4844401
210 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1059.001 PowerShell T1059.003 Windows Command Shell T1204.002 Malicious File

This XLSM file contains Excel 4.0 macros that utilize dangerous API calls like CALL and RETURN. The VBA script, specifically the `VDecso` function, appears to be designed to decode and execute a command. The `CALL` function in the XLM sheet is used to execute `regsvr` with a constructed command line, indicating an attempt to download and run a payload. The presence of hidden sheets and the use of ActiveX events further suggest a malicious intent to conceal and execute code.

Heuristics 6

  • VBA ActiveX event runs worksheet-decoded XLM formulas critical OLE_VBA_ACTIVEX_XLM_CELL_STAGER
    VBA code attached to an ActiveX/UserForm event reconstructs formula text from worksheet constants using Split/Replace/Mid or character shifting, then executes it through ExecuteExcel4Macro or Run. This is a high-confidence malware stager that hides XLM formula execution in sheet cells; it is not a document-parser CVE.
  • 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: CALL, 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 vbaProject.bin — VBA macros present
  • 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

Extracted artifacts 4

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
5ab6aa30ba0311b6d8e37f1685a6299796906b88954fb7aea44ebbe46585993e		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 1753 bytes
vbaProject_00.bin
173e0809de1f248d97677959b33b31fc7d35b0060269fed0ae53f8f74d92482a		 vba-project OOXML VBA project: xl/vbaProject.bin 18432 bytes
emf_00.emf
1f4b6aac9bcc91d9dad450240727fa7c7cec78eea965f7cfcef298fbb000c2f8		 ooxml-emf OOXML EMF part: xl/media/image1.emf 1976 bytes
xlm_sheet_00.xml
72c739fd39ccb7885e2deb9eec4906e8d80a8c3ab1e6a055edc6dff1da30a7d2		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1204 bytes

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