Malicious Office (OOXML) — malware analysis report

Static analysis result for SHA-256 9e7b570f67b9e41b…

MALICIOUS

Office (OOXML)

81.1 KB Created: 2021-04-09 12:11:10 UTC Authoring application: Microsoft Excel 16.0300
MD5: ca4ec0bf86733adc83312be9f7a8aea1 SHA-1: 6849e980ca84e4c1cd71572fba3cb71b6762b511 SHA-256: 9e7b570f67b9e41b8149869a182bd9a4d3d7f5fcd2bedec42f32c907a05867e3
210 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1566.001 Spearphishing Attachment T1203 Exploitation for Client Execution

This Excel document contains an obfuscated VBA macro designed to execute automatically upon opening (Workbook_Open). The macro utilizes CreateObject and potentially other execution methods to download and run a payload from the URL https://register.assayfit.com/. The presence of a Workbook_Open macro and the use of CreateObject strongly suggest a malicious intent to compromise the user's system.

Heuristics 7

  • 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)
  • 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 https://register.assayfit.com/
    • http://stackoverflow.com/questions/6136798/vba-shell-function-in-office-2011-for-mac

Extracted artifacts 2

Files carved from inside the sample during analysis.

FilenameKindSourceSize
macros.bas
42d61cebe77b9186d9e806df7dd2592909f283d896356b5cfa81f1bb159375c4		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 27301 bytes
vbaProject_00.bin
5c5cf9c1920bbf4fbe1c311edfadf47b63f962110f8d24d6fa828d743603d538		 vba-project OOXML VBA project: xl/vbaProject.bin 100864 bytes

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