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

Static analysis result for SHA-256 4b64c4353518c153…

MALICIOUS

Office (OOXML) / .XLSM

200.0 KB Created: 2021-09-13 09:41:09 UTC Authoring application: Microsoft Excel 12.0000 First seen: 2021-09-23
MD5: e1efa2d0ace1998e386d03efd18cfced SHA-1: 064317daaf132f0585bd0565eaaf4f2bfc2675dc SHA-256: 4b64c4353518c153432f1e315a4c32e3a2910278a99d3cc6418586c3e86a8558
190 Risk Score

Malware Insights

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

This Excel 4.0 macro-enabled spreadsheet (XLSM) utilizes dangerous functions such as FOPEN, FWRITE, FCLOSE, EXEC, and HALT. These functions are indicative of a downloader or dropper, likely intended to fetch and execute a second-stage payload. The presence of an Auto_Open defined name further suggests automatic execution upon opening the document. The specific functions used point towards a mechanism for writing and executing arbitrary code.

Heuristics 5

  • 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.
  • Excel 4.0 Auto_Open defined name critical OOXML_XLM_AUTOOPEN_DEFINEDNAME
    Workbook defines _xlnm.Auto_Open or _xlnm.Auto_Close while containing an XLM macro sheet. This is the OOXML/XLSB auto-execution shape for Excel 4.0 macros.
  • Dangerous XLM formula APIs: FOPEN, FWRITE, FCLOSE, EXEC, 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

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.xml
209a9653727c8aa40408d426796778d29a3c2c6010085a9b086d2b2ea3d63e5c		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1489 bytes

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