Suspicious newly registered reply-to domain with engaging financial or urgent language
Detects messages from a mismatched newly registered Reply-to domain that contain a financial or urgent request, or a request and an NLU tag with medium to high confidence, from an untrusted sender. This technique is typically observed in Vendor impersonation.
Sublime rule (View on GitHub)
1name: "Suspicious newly registered reply-to domain with engaging financial or urgent language"
2description: |
3 Detects messages from a mismatched newly registered Reply-to domain that contain a financial or urgent request, or a request and
4 an NLU tag with medium to high confidence, from an untrusted sender. This technique is typically observed in Vendor impersonation.
5type: "rule"
6severity: "medium"
7source: |
8 type.inbound
9 and length(body.current_thread.text) < 5000
10 and any(headers.reply_to,
11 // mismatched reply-to and sender domain
12 .email.domain.root_domain != sender.email.domain.root_domain
13 // newly registered reply-to domain
14 and network.whois(.email.domain).days_old <= 30
15 )
16 // request is being made
17 and any(ml.nlu_classifier(body.current_thread.text).entities,
18 .name == "request"
19 )
20 // there's financial/urgency OR a tag of medium/high confidence
21 and (
22 any(ml.nlu_classifier(body.current_thread.text).entities,
23 .name in ("financial", "urgency")
24 )
25 or any(ml.nlu_classifier(body.current_thread.text).tags,
26 .name is not null and .confidence in ("medium", "high")
27 )
28 )
29 and (
30 not profile.by_sender().solicited
31
32 //
33 // This rule makes use of a beta feature and is subject to change without notice
34 // using the beta feature in custom rules is not suggested until it has been formally released
35 //
36 or not beta.profile.by_reply_to().solicited
37
38 or (
39 profile.by_sender().any_messages_malicious_or_spam
40 and not profile.by_sender().any_false_positives
41 )
42 )
43 // negate highly trusted sender domains unless they fail DMARC authentication
44 and (
45 (
46 sender.email.domain.root_domain in $high_trust_sender_root_domains
47 and not headers.auth_summary.dmarc.pass
48 )
49 or sender.email.domain.root_domain not in $high_trust_sender_root_domains
50 )
51
52attack_types:
53 - "BEC/Fraud"
54tactics_and_techniques:
55 - "Social engineering"
56detection_methods:
57 - "Content analysis"
58 - "Header analysis"
59 - "Natural Language Understanding"
60 - "Sender analysis"
61 - "URL analysis"
62 - "Whois"
63id: "db4d9bb3-0eca-5525-9a99-7c1c773b580f"