MAL_G_Backdoor_BRICKSTORM_2

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:
      // $obf_func = /[a-z]{20}\/[a-z]{20}\/[a-z]{20}\/[a-z]{20}.go/
      $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*)
      )
}