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

Static analysis result for SHA-256 0f836aeb12f4fdc3…

MALICIOUS

Office (OOXML) / .XLSM

436.6 KB Created: 2021-07-28 10:37:27 UTC Authoring application: Microsoft Excel 12.0000
MD5: 08651312169ab9bdcb4ea0d6dc6d47fe SHA-1: 696d2952dad7dc27f5013e66a17f0565a857bfb7 SHA-256: 0f836aeb12f4fdc3d5be18985e9fdf7a2124b4326b2b88a6a44bb34b5b0cf5b0
208 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1218.005 Client Execution: Mshta

The sample is an XLSM file containing a Workbook_Open macro that is heavily obfuscated. The macro constructs a path using Environ() and Cells() and then writes a script to that path. It then uses CreateObject to execute mshta with the constructed script path. The script appears to be a SCT file, which is typically executed by mshta. This indicates a downloader or dropper functionality.

Heuristics 6

  • Obfuscated auto-exec VBA loader critical OLE_VBA_OBFUSCATED_AUTOEXEC_LOADER
    Auto-exec VBA reconstructs strings with a heavy custom decoder (numeric char-array, repeated hex-string decode, or junk-token Replace removal) and feeds them to a COM-instantiation or execution sink. This obfuscated-loader shape keeps CreateObject/Shell/URL indicators out of the macro source.
  • Workbook_Open macro high OLE_VBA_WBOPEN
    Workbook_Open macro
  • CreateObject call high OLE_VBA_CREATEOBJ
    CreateObject call
  • VBA p-code auto-exec with execution tokens high OLE_VBA_PCODE_AUTOEXEC_EXEC
    Compiled VBA/cache stream contains an auto-execution token together with shell/download/object-execution tokens. This catches p-code-only or source-extraction-failure macro documents where visible source is unavailable.
  • VBA project inside OOXML medium OOXML_VBA
    Document contains a VBA project — VBA macros present
  • Environ() call (env variable access) low OLE_VBA_ENVIRON
    Environ() call (env variable access)

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
21bf8e17222f2ac7d4446182f5d8afd86cb378d51e7000e50482f9519adb9531		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 1125 bytes
vbaProject_00.bin
1567171d9680d3ff28a3954467c8937d3443d66cc632af451300d8a412d8b1be		 vba-project OOXML VBA project: xl/vbaProject.bin 9216 bytes

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