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

Static analysis result for SHA-256 67d6f9447a1030cc…

MALICIOUS

Office (OOXML) / .XLSX

212.1 KB Created: 2021-04-29 16:14:12 UTC Authoring application: Microsoft Excel 15.0300
MD5: 964eba8730fd642092ff06f1b5efac4c SHA-1: 1de0b6e144b91c7c7ca5369b0a69ddd7cf947b71 SHA-256: 67d6f9447a1030cc7e7647fb5f15505a59b0957519d50717d81db96287c76ac4
448 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File T1105 Ingress Tool Transfer

The sample is an Excel document containing a Workbook_Open macro that utilizes WScript.Shell and CreateObject to download and execute a payload. The macro appears obfuscated, and ClamAV detections indicate a known malware agent. The primary technique observed is the use of VBA to download and execute a secondary artifact.

Heuristics 10

  • WScript.Shell usage critical OLE_VBA_WSCRIPT
    WScript.Shell usage
  • VBA downloads and writes a file to disk critical OLE_VBA_HTTP_DROP_EXEC
    VBA reads an HTTP response body and writes it to disk (ADODB.Stream SaveToFile). Combined with the auto-exec/Shell paths this is a download-drop dropper even when the COM ProgIDs are built dynamically to evade keyword scanning.
  • 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.
  • ClamAV: Win.Malware.Agent-9904903-0 critical CLAMAV_DETECTION
    ClamAV detected this file as malware: Win.Malware.Agent-9904903-0
  • ClamAV detection on extracted artifact critical EXTRACTED_FILE_CLAMAV
    ClamAV flagged at least one file extracted from inside this sample. Even when the wrapping document carries no AV detection of its own, a hit on the carved artifact is a strong indicator the sample is a delivery vehicle.
  • 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
846cd090eba239bc7141754622239f6511d6178279a6758966d9e1f77ad71adb		 vba-macro oletools.olevba.extract_macros (decoded VBA source from OOXML) 10250 bytes
vbaProject_00.bin
89e7409e8d87bb96efc2c96c81f8520a114ecf154df676aa4f1ed29432f23d22		 vba-project OOXML VBA project: xl/vbaProject.bin 60928 bytes
Detection
ClamAV: Win.Malware.Agent-9904903-0
Obfuscation or payload: unlikely

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