SUSP_Scheduled_Task_BigSize

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

Detects suspiciously big scheduled task XML file as seen in combination with embedded base64 encoded PowerShell code

rule SUSP_Scheduled_Task_BigSize {
   meta:
      description = "Detects suspiciously big scheduled task XML file as seen in combination with embedded base64 encoded PowerShell code"
      author = "Florian Roth (Nextron Systems)"
      reference = "Internal Research"
      date = "2018-12-06"
      id = "61b07b30-1058-5a53-99e7-2c48ec9d23b5"
   strings:
      $a0 = "<Task version=" ascii wide
      $a1 = "xmlns=\"http://schemas.microsoft.com/windows/" ascii wide

      $fp1 = "</Counter><Counter>" wide
      $fp2 = "Office Feature Updates Logon" wide
      $fp3 = "Microsoft Shared" fullword wide
   condition:
      uint16(0) == 0xfeff and filesize > 20KB and all of ($a*) and not 1 of ($fp*)
}

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

a9a198cc-cd4b-410b-8873-ba2fe5b4a5cd

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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

[[ reason ]]

What does this mean?

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.

[[ reason ]]

What do these messages mean?

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

[[ currentRule.title ]]

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