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

Static analysis result for SHA-256 3ea6b6b3df93ce4d…

MALICIOUS

Office (OOXML) / .XLSM

290.0 KB Created: 2021-08-16 09:36:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: a55646de5abba69c44490fbb2cde44ae SHA-1: c0dda6dbaa6f3de0dc4a55769a0c4b7e6cd1d0f7 SHA-256: 3ea6b6b3df93ce4d876edb88cf5c5e67a0fd7bae402f64bf643f98621cd0cc59
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

The sample is an XLSM file containing Excel 4.0 macros. The macros utilize dangerous functions like FOPEN, FWRITE, and FCLOSE to write a script to disk at C:\ProgramData\VnYzDDxhdyM.sct. The EXEC function is then used to execute this script, indicating a downloader or dropper functionality.

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
13c36435ea398f62b62aacb2a4a7ef875abbf435b80123d450aaadff61333a87		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.xml 1129335 bytes

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