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 first time 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 first time sender. This technique is typically observed in Vendor impersonation.
5type: "rule"
6severity: "medium"
7source: |
8 type.inbound
9 and any(headers.reply_to,
10 // mismatched reply-to and sender domain
11 .email.domain.root_domain != sender.email.domain.root_domain
12
13 // newly registered reply-to domain
14 and beta.whois(.email.domain).days_old <= 30
15 )
16
17 // request is being made
18 and any(ml.nlu_classifier(body.current_thread.text).entities, .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, .name in ("financial", "urgency"))
23 or any(ml.nlu_classifier(body.current_thread.text).tags,
24 .name is not null and .confidence in ("medium", "high")
25 )
26 )
27
28 // first-time sender
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 - "BEC/Fraud"
41tactics_and_techniques:
42 - "Social engineering"
43detection_methods:
44 - "Content analysis"
45 - "Header analysis"
46 - "Natural Language Understanding"
47 - "Sender analysis"
48 - "URL analysis"
49 - "Whois"
50id: "db4d9bb3-0eca-5525-9a99-7c1c773b580f"