Lookalike sender domain (untrusted sender)

name: "Lookalike sender domain (untrusted sender)"
description: |
  Sender's domain is a lookalike of one of your organization's domains and is untrusted.
type: "rule"
severity: "high"
source: |
  type.inbound
  and length(sender.email.domain.sld) > 3
  and sender.email.domain.domain not in $org_domains
  and any($org_domains,
          // this rule can be duplicated in order to tune the threshold
          strings.ilevenshtein(sender.email.domain.domain, .) == 1
  )
  and (
    (
      profile.by_sender_email().prevalence in ("new", "outlier")
      and not profile.by_sender_email().solicited
    )
    or (
      profile.by_sender_email().any_messages_malicious_or_spam
      and not profile.by_sender_email().any_messages_benign
    )
  )
  
  // negate highly trusted sender domains unless they fail DMARC authentication
  and (
    (
      sender.email.domain.root_domain in $high_trust_sender_root_domains
      and not headers.auth_summary.dmarc.pass
    )
    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
  )
  and not profile.by_sender_email().any_messages_benign
attack_types:
  - "BEC/Fraud"
  - "Credential Phishing"
  - "Malware/Ransomware"
tactics_and_techniques:
  - "Lookalike domain"
  - "Social engineering"
detection_methods:
  - "Sender analysis"
id: "67721993-4f5d-575b-970b-3ced67a874fa"