VIP Impersonation via Google Group relay with suspicious indicators

 1name: "VIP Impersonation via Google Group relay with suspicious indicators"
 2description: "Public Google Groups can be used to impersonate internal senders, while the reply to address is not under organizational control, leading to fraud, credential phishing, or other unwanted outcomes."
 3type: "rule"
 4severity: "high"
 5source: |
 6  (type.inbound or type.internal)
 7  and sender.email.domain.root_domain in $org_domains
 8  
 9  // subject, sender or reply to contains a VIP
10  and (
11    any(headers.reply_to,
12        any($org_vips, strings.contains(.display_name, ..display_name))
13    )
14    or any($org_vips, strings.contains(subject.subject, .display_name))
15    or any($org_vips, strings.contains(sender.display_name, .display_name))
16  )
17  and any(headers.hops,
18          any(.fields,
19              strings.istarts_with(.name,
20                                   "X-Authenticated-Sender",
21                                   "X-Sender",
22                                   "X-Original-Sender"
23              )
24          )
25  )
26  
27  // reply to return path mismatch and not org domain
28  and any(headers.reply_to,
29          .email.domain.root_domain != headers.return_path.domain.root_domain
30          and .email.domain.root_domain not in $org_domains
31  )
32  
33  // googlegroups found in hops
34  and any(headers.hops,
35          .index == 0 and any(.fields, strings.icontains(.value, "googlegroups"))
36  )
37  
38  // financial nlu entity in current thread
39  and 3 of (
40    any(ml.nlu_classifier(body.current_thread.text).entities,
41        .name == "financial"
42    ),
43  
44    // invoice entity in display_text
45    any(ml.nlu_classifier(body.current_thread.text).tags, .name == "invoice"),
46  
47    // fake thread
48    (
49      (subject.is_forward or subject.is_reply)
50      and (
51        (length(headers.references) == 0 and headers.in_reply_to is null)
52        or headers.in_reply_to is null
53      )
54    ),
55  
56    // reply-to is freemail
57    any(headers.reply_to, .email.domain.domain in $free_email_providers),
58  
59    // reply-to is not in $recipient_emails
60    any(headers.reply_to, .email.email not in $recipient_emails),
61  
62    // dmarc authentication is freemail provider
63    headers.auth_summary.dmarc.details.from.root_domain in $free_email_providers
64  )  
65attack_types:
66  - "BEC/Fraud"
67  - "Credential Phishing"
68  - "Malware/Ransomware"
69tactics_and_techniques:
70  - "Evasion"
71  - "Free email provider"
72  - "Impersonation: Employee"
73  - "Social engineering"
74  - "Spoofing"
75detection_methods:
76  - "Content analysis"
77  - "Header analysis"
78  - "Natural Language Understanding"
79  - "Sender analysis"
80id: "57f9cd3b-ddac-5ef5-96dd-374dbd03f5cd"