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

Static analysis result for SHA-256 844f17d3c5ded793…

MALICIOUS

Office (OOXML) / .XLSM

220.6 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 5d8aab5917dd30e92bc88e58fe741d47 SHA-1: b609a6b873e569e5dace2c90675575b6763dd40f SHA-256: 844f17d3c5ded793e7c5f1a2223a50a828a30d17da9b008a7eadd584ce2f0528
250 Risk Score

Malware Insights

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

The sample is an Excel 4.0 macro sheet that leverages dangerous functions like EXEC and FOPEN. The script reconstructs the path 'C:\ProgramData\HcUdedk.sct' and then attempts to execute it using 'EXEC(CONCATENATE(CHAR(77), CHAR(83), CHAR(72), CHAR(84), CHAR(65), CONCATENATE(A3, A1)))'. This indicates a downloader or dropper functionality, aiming to execute a secondary payload from a local path.

Heuristics 6

  • 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: EXEC, HALT, FOPEN, FWRITE, FCLOSE 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.
  • ClamAV: Xls.Downloader.DridexCyan08210-9887648-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.DridexCyan08210-9887648-0
  • 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
cebc09ce35448d44ac8261b6fa9dff21fd15960751a87cfc7fb65563d01a7dce		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 256123 bytes

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