Suspicious Recipients pattern with no Compauth pass and suspicious content

 1name: "Suspicious Recipients pattern with no Compauth pass and suspicious content"
 2description: "Detects messages with undisclosed recipients (likely all bcc), where the Compauth verdict is not 'pass', and ML has identified suspicious language or credential phishing links."
 3type: "rule"
 4severity: "medium"
 5source: |
 6  type.inbound
 7  and (length(recipients.to) == 0 or all(recipients.to, .display_name == "Undisclosed recipients"))
 8  and length(recipients.cc) == 0
 9  and length(recipients.bcc) == 0
10  and 2 of (
11    (
12      any(headers.hops,
13          .authentication_results.compauth.verdict is not null
14          and .authentication_results.compauth.verdict not in ("pass", "softpass")
15      )
16    ),
17    (
18      any(ml.nlu_classifier(body.current_thread.text).intents,
19          .name in ("bec", "cred_theft", "advance_fee") and .confidence == "high"
20      )
21    ),
22    (
23      any(body.links,
24          any([ml.link_analysis(.)],
25              .credphish.disposition == "phishing" and .credphish.confidence in ("high")
26          )
27      )
28    )
29  )
30  and (
31    profile.by_sender().prevalence in ("new", "outlier")
32    or (
33      profile.by_sender().any_messages_malicious_or_spam
34      and not profile.by_sender().any_false_positives
35    )
36  )
37  // negate highly trusted sender domains unless they fail DMARC authentication
38  and (
39    (
40      sender.email.domain.root_domain in $high_trust_sender_root_domains
41      and not headers.auth_summary.dmarc.pass
42    )
43    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
44  )  
45detection_methods:
46  - "Content analysis"
47  - "Computer Vision"
48  - "Header analysis"
49  - "Natural Language Understanding"
50  - "URL analysis"
51  - "URL screenshot"
52id: "34fb65f6-03e8-5752-b602-4f294172b5db"