Callback Phishing in body or attachment (untrusted sender)

 1name: "Callback Phishing in body or attachment (untrusted sender)"
 2description: |
 3    Detects callback scams by analyzing text within images of receipts or invoices from untrusted senders.
 4type: "rule"
 5severity: "medium"
 6source: |
 7  type.inbound
 8  and length(attachments) < 5
 9  and (
10    any(attachments,
11        (.file_type in $file_types_images or .file_type == "pdf")
12        and any(file.explode(.),
13  
14                // exclude images taken with mobile cameras and screenshots from android
15                not any(.scan.exiftool.fields,
16                        .key == "Model"
17                        or (
18                          .key == "Software"
19                          and strings.starts_with(.value, "Android")
20                        )
21                        or (.key == "UserComment" and .value == "Screenshot")
22                )
23                and any(ml.nlu_classifier(.scan.ocr.raw).intents,
24                        .name == "callback_scam" and .confidence == "high"
25                )
26        )
27    )
28    or any(ml.nlu_classifier(body.current_thread.text).intents,
29           .name in ("callback_scam")
30           and .confidence == "high"
31           and length(body.current_thread.text) < 1500
32    )
33  )
34  and not (
35    any(headers.domains, .domain == "smtp-out.gcp.bigcommerce.net")
36    and strings.icontains(body.html.raw, "bigcommerce.com")
37  )
38  and (
39    (
40      profile.by_sender().prevalence in ("new", "outlier")
41      and not profile.by_sender().solicited
42    )
43    or (
44      profile.by_sender().any_messages_malicious_or_spam
45      and not profile.by_sender().any_false_positives
46    )
47  )
48  
49  // negate highly trusted sender domains unless they fail DMARC authentication
50  and (
51    (
52      sender.email.domain.root_domain in $high_trust_sender_root_domains
53      and not headers.auth_summary.dmarc.pass
54    )
55    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
56  )  
57
58
59attack_types:
60  - "Callback Phishing"
61tactics_and_techniques:
62  - "Out of band pivot"
63  - "Social engineering"
64detection_methods:
65  - "Content analysis"
66  - "File analysis"
67  - "Optical Character Recognition"
68  - "Natural Language Understanding"
69  - "Sender analysis"
70id: "b93c6f94-c9a3-587a-8eb5-6856754f8222"