SUSP_DOC_RTF_ExternalResource_EMAIL_Jun22

rule SUSP_DOC_RTF_ExternalResource_EMAIL_Jun22 {
   meta:
      description = "Detects a suspicious pattern in RTF files which downloads external resources as seen in CVE-2022-30190 / Follina exploitation inside e-mail attachment"
      author = "Christian Burkard"
      date = "2022-06-01"
      reference = "https://doublepulsar.com/follina-a-microsoft-office-code-execution-vulnerability-1a47fce5629e"
      score = 70
      id = "3ddc838c-8520-5572-9652-8cb823f83e27"
   strings:
      /* <Relationships */
      $sa1 ="PFJlbGF0aW9uc2hpcH" ascii
      $sa2 ="xSZWxhdGlvbnNoaXBz" ascii
      $sa3 ="8UmVsYXRpb25zaGlwc" ascii
      /* TargetMode="External" */
      $sb1 ="VGFyZ2V0TW9kZT0iRXh0ZXJuYWwi" ascii
      $sb2 ="RhcmdldE1vZGU9IkV4dGVybmFsI" ascii
      $sb3 ="UYXJnZXRNb2RlPSJFeHRlcm5hbC" ascii
      /* .html!" */
      $sc1 ="Lmh0bWwhI" ascii
      $sc2 ="5odG1sIS" ascii
      $sc3 ="uaHRtbCEi" ascii
   condition:
      filesize < 400KB
      and 1 of ($sa*)
      and 1 of ($sb*)
      and 1 of ($sc*)
}