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

Static analysis result for SHA-256 4a8d3e1f28dcddd8…

MALICIOUS

Office (OOXML) / .XLSM

241.0 KB Created: 2021-09-13 09:41:09 UTC Authoring application: Microsoft Excel 12.0000
MD5: f2bec56e09883a139201183f00f400a4 SHA-1: 6183a3935e2552484f53f74a6d340f8f451fe0b7 SHA-256: 4a8d3e1f28dcddd8177e378b14b49dc0e23dad9772931f6616ce64ad17585fa7
190 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic for Applications T1204.002 Malicious File T1059.001 PowerShell T1105 Ingress Tool Transfer T1059.003 Windows Command Shell

The sample is an Excel 4.0 macro-enabled spreadsheet. It utilizes dangerous XLM functions such as FOPEN, FWRITE, FCLOSE, and EXEC to download and execute a second-stage payload. The macro sheet contains formulas that appear to be constructing or retrieving a payload for execution via the EXEC function, followed by HALT to terminate the macro. The specific payload URL or content is not directly visible in the provided formulas, but the pattern strongly suggests a downloader.

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
2c224e2267227efb8b8755a39357dd2a062c1a8c0c8d75ed82e45f279a61216b		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1486 bytes

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