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

Static analysis result for SHA-256 f4c15b1eee06d45f…

MALICIOUS

Office (OOXML) / .XLSM

44.8 KB Created: 2020-12-07 12:50:14 UTC Authoring application: Microsoft Excel 16.0300
MD5: d5b40faa134ee1e73233e521ac476cdd SHA-1: ef4b0244623220dabbc9317b930df957fa9c48d9 SHA-256: f4c15b1eee06d45fa6115ddcfeb24bdacf54570352e0cb713e1c5895089dae1d
210 Risk Score

Malware Insights

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

This XLSM file contains Excel 4.0 macros that leverage dangerous functions like RETURN() to execute arbitrary code. The VBA code appears to be designed to decode and execute these XLM macros. The primary intent is to download and execute a second-stage payload, as indicated by the use of functions that can call Win32 APIs. The specific payload or delivery mechanism beyond the initial macro execution is not fully discernible from the provided scripts.

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
afa23a2c616c75c1ad0a2d30538f467ef11689ac2e18af2cabe5fd6661f5c688		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 1765 bytes
vbaProject_00.bin
dafa43c1188b2a0f54ac7ee2687235a97945837d9869392ad9c7f32e63932017		 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
586238f176ceb1ad8bfef7b63ecf553c836381db50e18a80fe41fb0bce10e31a		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 959 bytes

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