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

Static analysis result for SHA-256 3aeb9cf319425bd4…

MALICIOUS

Office (OOXML) / .XLSM

248.7 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 120dc19fa296ef630b6d8a91abed7d2d SHA-1: 1fb90e4d2977383a2283c108b51991abeae833e2 SHA-256: 3aeb9cf319425bd4df2d579f28aa1fd61aee9fa37b2c02b035f05c19b823a584
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 file is an XLSM document containing Excel 4.0 macros. Critical heuristics indicate the use of dangerous XLM functions like CALL, EXEC, and REGISTER, which are used to directly invoke Win32 APIs. The macro code reconstructs the string "C:\ProgramData\blhPqfisEhh.sct" and writes it to disk, likely to be executed as a second-stage payload. This indicates a downloader or dropper functionality.

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: 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.
  • ClamAV: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Xls.Downloader.Trojan-a0425f7f2000faff-a0425f7f2000faff-9950268-0
  • 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
6157119bd1547fa072d5c374f35a25394095b27dfa22302f644f241bfe04e59e		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 817866 bytes

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