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

Static analysis result for SHA-256 c232467372fccd98…

MALICIOUS

Office (OOXML) / .XLSM

35.8 KB Created: 2020-11-24 11:52:57 UTC Authoring application: Microsoft Excel 16.0300
MD5: 21f14fd3e3959e8ee834ea24f931c0b3 SHA-1: 31820ca6a45adf387816cc4ddc97de9180b0e52f SHA-256: c232467372fccd98fc562479dc657d524caae15a5455fc0b1b8e03af13fa2fce
210 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

This XLSM file contains Excel 4.0 macros that leverage the dangerous `RETURN()` function, which can be used to execute arbitrary code. The VBA script decodes a string and then executes it as an Excel 4.0 macro sheet. The `RETURN()` function in the macro sheet is the primary mechanism for payload execution. The script also attempts to hide its activity by using hidden sheets and obfuscated code. The specific payload or download URL is not directly visible in the provided evidence, leading to a slightly reduced confidence.

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: 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
cb97cfc2f47a0d63ed380127ea82e43ea27ba2a8845a11784448ead1cd07edac		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 1276 bytes
vbaProject_00.bin
43e3675f65bf34a9127712b2c42af06a4cb0cb0dab2a039ce9b6d0eeb285a151		 vba-project OOXML VBA project: xl/vbaProject.bin 12288 bytes
emf_00.emf
76f287b1e3251b7e0e5ba27bfb05b35831150cc665de00f9fd2d807e2d2a028d		 ooxml-emf OOXML EMF part: xl/media/image1.emf 1976 bytes
xlm_sheet_00.xml
88f59ee5f5da80d8bce156475c2909c915695d45e564a6de3d61d80b4c007556		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 971 bytes

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