Impersonation: Recipient SLD in sender's email address local part

 1name: "Impersonation: Recipient SLD in sender's email address local part"
 2type: "rule"
 3severity: "low"
 4description: |
 5  The sender's email address local part contains the recipients SLD,
 6  the sender's domain is not a known org domain, and it's a first time sender.  
 7source: |
 8  type.inbound
 9  // check that there's at least 1 sus attachment, link, or body text
10  and (
11    length(attachments) > 0
12    // this must be run in user environments to not flag,
13    // not the Analyzer
14    or any(body.links, .href_url.domain.domain not in $org_domains)
15    or any(ml.nlu_classifier(body.current_thread.text).intents,
16           .name != "benign" and .confidence == "high"
17    )
18  )
19  and (
20    any(recipients.to,
21        (
22          strings.contains(sender.email.local_part, .email.domain.sld)
23          // checking to ensure no FPs, like "me" in "me.com"
24          and length(.email.domain.sld) > 3
25        )
26    )
27  )
28  and sender.email.domain.root_domain not in $org_domains
29  and (
30    (
31      sender.email.domain.root_domain in $free_email_providers
32      and sender.email.email not in $sender_emails
33    )
34    or (
35      sender.email.domain.root_domain not in $free_email_providers
36      and sender.email.domain.domain not in $sender_domains
37    )
38  )  
39attack_types:
40  - "Credential Phishing"
41tactics_and_techniques:
42  - "Social engineering"
43detection_methods:
44  - "Header analysis"
45  - "Sender analysis"
46id: "926f3b53-415c-590e-b5f7-a15c6d9e62c2"