MAL_G_APT_Backdoor_BRICKSTORM_2

YARA detection rule by Google Threat Intelligence Group (GTIG) (modified by Florian Roth) · NOASSERTION

Detects BRICKSTORM backdoor used by APT group UNC5221 (China Nexus)

rule MAL_G_Backdoor_BRICKSTORM_2 {
   meta:
      description = "Detects BRICKSTORM backdoor used by APT group UNC5221 (China Nexus)"
      author = "Google Threat Intelligence Group (GTIG) (modified by Florian Roth)"
      date = "2025-09-25"
      score = 75
      reference = "https://cloud.google.com/blog/topics/threat-intelligence/brickstorm-espionage-campaign"
      id = "03618840-c3f3-5ba6-983b-181a855d506b"
   strings:
            $decr1 = { 0F B6 4C 04 ?? 0F B6 54 04 ?? 31 D1 88 4C 04 ?? 48 FF C0 [0-4] 48 83 F8 ?? 7C }
      $decr2 = { 40 88 7C 34 34 48 FF C3 48 FF C6 48 39 D6 7D 18 0F B6 3B 48 39 CE 73 63 44 0F B6 04 30 44 31 C7 48 83 FE 04 72 DA }
      $decr3 = { 0F B6 54 0C ?? 0F B6 5C 0C ?? 31 DA 88 14 08 48 FF C1 48 83 F9 ?? 7C E8 }

      $str1 = "main.selfWatcher"
      $str2 = "main.copyFile"
      $str3 = "main.startNew"

      $str4 = "WRITE_LOG=true"
      $str5 = "WRITE_LOGWednesday"
      $str6 = "vami-httpdvideo/webm"
      $str7 = "/opt/vmware/sbin/"
      $str8 = "/home/vsphere-ui/"
      $str9 = "/opt/vmware/sbin/vami-http"
      $str10 = "main.getVFromEnv"
   condition:
      uint32(0) == 0x464c457f
      and filesize < 10MB
      and (
         1 of ($decr*)
         and 1 of ($str*)
         or 5 of ($str*)
      )
}

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

07d6aea1-2deb-42bb-a1ab-82f9b7b382fd

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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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