Body: Business Email Compromise (BEC) attempt from first-time sender

 1name: "Body: Business Email Compromise (BEC) attempt from first-time sender"
 2description: |
 3    Detects potential Business Email Compromise (BEC) attacks by analyzing text within the email body from first-time senders.
 4type: "rule"
 5severity: "medium"
 6source: |
 7  type.inbound
 8  and any(ml.nlu_classifier(body.current_thread.text).intents,
 9          .name in ("bec") and .confidence == "high"
10  )
11  // negating legit replies
12  and not (
13    (
14      strings.istarts_with(subject.subject, "RE:")
15      // out of office auto-reply
16      // the NLU model will handle these better natively soon
17      or strings.istarts_with(subject.subject, "Automatic reply:")
18    )
19    and (
20      length(headers.references) > 0
21      or any(headers.hops, any(.fields, strings.ilike(.name, "In-Reply-To")))
22    )
23  )
24  // first-time sender
25  and (
26    (
27      sender.email.domain.root_domain in $free_email_providers
28      and sender.email.email not in $sender_emails
29    )
30    or (
31      sender.email.domain.root_domain not in $free_email_providers
32      and sender.email.domain.domain not in $sender_domains
33    )
34  )  
35attack_types:
36  - "BEC/Fraud"
37tactics_and_techniques:
38  - "Social engineering"
39detection_methods:
40  - "Content analysis"
41  - "Header analysis"
42  - "Natural Language Understanding"
43  - "Sender analysis"
44id: "96d4c35a-ca53-559e-9db3-349dbbdffc20"