Lookalike sender domain (untrusted sender)

 1name: "Lookalike sender domain (untrusted sender)"
 2description: |
 3    Sender's domain is a lookalike of one of your organization's domains and is untrusted.
 4type: "rule"
 5severity: "high"
 6source: |
 7  type.inbound
 8  and length(sender.email.domain.sld) > 3
 9  and sender.email.domain.domain not in $org_domains
10  and any($org_domains,
11          // this rule can be duplicated in order to tune the threshold
12          strings.ilevenshtein(sender.email.domain.domain, .) == 1
13  )
14  and (
15    (
16      profile.by_sender_email().prevalence in ("new", "outlier")
17      and not profile.by_sender_email().solicited
18    )
19    or (
20      profile.by_sender_email().any_messages_malicious_or_spam
21      and not profile.by_sender_email().any_messages_benign
22    )
23  )
24  
25  // negate highly trusted sender domains unless they fail DMARC authentication
26  and not (
27    sender.email.domain.root_domain in $high_trust_sender_root_domains
28    and coalesce(headers.auth_summary.dmarc.pass, false)
29  )
30  and not profile.by_sender_email().any_messages_benign  
31attack_types:
32  - "BEC/Fraud"
33  - "Credential Phishing"
34  - "Malware/Ransomware"
35tactics_and_techniques:
36  - "Lookalike domain"
37  - "Social engineering"
38detection_methods:
39  - "Sender analysis"
40id: "67721993-4f5d-575b-970b-3ced67a874fa"