SUSP_VBA_FileSystem_Access

YARA detection rule by Florian Roth (Nextron Systems) · NOASSERTION

Detects suspicious VBA that writes to disk and is activated on document open

rule SUSP_VBA_FileSystem_Access {
   meta:
      description = "Detects suspicious VBA that writes to disk and is activated on document open"
      author = "Florian Roth (Nextron Systems)"
      reference = "Internal Research"
      date = "2019-06-21"
      score = 60
      hash1 = "52262bb315fa55b7441a04966e176b0e26b7071376797e35c80aa60696b6d6fc"
      id = "91241b91-ca3f-5817-bf78-550fe015b467"
   strings:
      $s1 = "\\Common Files\\Microsoft Shared\\" wide
      $s2 = "Scripting.FileSystemObject" ascii

      $a1 = "Document_Open" ascii
      $a2 = "WScript.Shell" ascii
      $a3 = "AutoOpen" fullword ascii
   condition:
      uint16(0) == 0xcfd0 and filesize < 100KB and all of ($s*) and 1 of ($a*)
}

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

dbe68d98-6320-482a-a869-5841a6ad40f4

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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