APT_MAL_Gopuram_Backdoor_Apr23

rule APT_MAL_Gopuram_Backdoor_Apr23 {
   meta:
      author = "X__Junior (Nextron Systems)"
      reference = "https://securelist.com/gopuram-backdoor-deployed-through-3cx-supply-chain-attack/109344/"
      description = "Detects Gopuram backdoor"
      date = "2023-02-24"
      hash1 = "beb775af5196f30e0ee021790a4978ca7a7ac2a7cf970a5a620ffeb89cc60b2c"
      hash2 = "97b95b4a5461f950e712b82783930cb2a152ec0288c00a977983ca7788342df7"
      score = 80
      id = "3ae5ddcb-5601-5dca-85dd-0a4772577fae"
   strings:
      $x1 = "%s\\config\\TxR\\%s.TxR.0.regtrans-m"  ascii
      $xop = { D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE } // operations on filename

      $opa1 = { 48 89 44 24 ?? 45 33 C9 45 33 C0 33 D2 89 5C 24 ?? 48 89 74 24 ?? 48 89 5C 24 ?? 89 7C 24 ?? FF 15 ?? ?? ?? ?? 85 C0 74 ?? 48 8B 4C 24 ?? 4C 8D 4C 24 ?? 44 8D 43 } // decrypt and Virtualprotect
      $opa2 = { 48 89 B4 24 ?? ?? ?? ?? 44 8D 43 ?? 33 D2 48 89 BC 24 ?? ?? ?? ?? 4C 89 B4 24 ?? ?? ?? ?? E8 ?? ?? ?? ?? 48 8B 4C 24 ?? E8 ?? ?? ?? ?? 48 8B 4C 24 ?? 45 33 C0 33 D2 8B F8 E8 ?? ?? ?? ?? 8D 4F ?? E8 ?? ?? ?? ?? 4C 8B 4C 24 ?? 44 8D 43 ?? 48 8B C8 8B D7 48 8B F0 44 8B F7 E8 ?? ?? ?? ?? 48 8B 4C 24 ?? E8  } // read file content
   condition:
      ( uint16(0) == 0x5A4D and filesize < 2MB
        and pe.characteristics & pe.DLL and 1 of ($x*)
      )
      or all of ($opa*)
}