Employee impersonation with urgent request (untrusted sender)

name: "Employee impersonation with urgent request (untrusted sender)"
description: |
  Sender is using a display name that matches the display name of someone in your organization.

  Detects potential Business Email Compromise (BEC) attacks by analyzing text within email body from untrusted senders.
type: "rule"
severity: "medium"
source: |
  type.inbound
  
  // ensure the display name contains a space to avoid single named process accounts eg. 'billing, payment'
  and strings.contains(sender.display_name, " ")
  and sender.display_name in~ $org_display_names
  and (
    any(ml.nlu_classifier(body.current_thread.text).intents,
        .name == "bec" and .confidence == "high"
    )
    or (
      (
        any(ml.nlu_classifier(body.current_thread.text).entities,
            .name == "urgency"
        )
        and any(ml.nlu_classifier(body.current_thread.text).entities,
                .name == "request"
        )
      )
      and not any(ml.nlu_classifier(body.current_thread.text).intents,
                  .name == "benign" and .confidence == "high"
      )
      and (
        (
          // there are intents returned
          any(ml.nlu_classifier(body.current_thread.text).intents, true)
          // short body that also contains an org display name
          or (
            length(body.current_thread.text) > 200
            and any(ml.nlu_classifier(body.current_thread.text).entities,
                    .name == "sender" and .text in~ $org_display_names
            )
          )
        )
        and not strings.istarts_with(subject.subject, "fwd:")
      )
    )
  )
  and (
    (
      profile.by_sender().prevalence in ("new", "outlier")
      and not profile.by_sender().solicited
    )
    or (
      profile.by_sender().any_messages_malicious_or_spam
      and not profile.by_sender().any_false_positives
    )
    or not headers.auth_summary.dmarc.pass
  )
  
  // negate org domains unless they fail DMARC authentication
  and (
    (
      sender.email.domain.root_domain in $org_domains
      and not headers.auth_summary.dmarc.pass
    )
    or sender.email.domain.root_domain not in $org_domains
  )
  
  // negate highly trusted sender domains unless they fail DMARC authentication
  and (
    (
      sender.email.domain.root_domain in $high_trust_sender_root_domains
      and not headers.auth_summary.dmarc.pass
    )
    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
  )
  and not profile.by_sender().any_false_positives
attack_types:
  - "BEC/Fraud"
tactics_and_techniques:
  - "Impersonation: Employee"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "Natural Language Understanding"
  - "Sender analysis"
id: "1ce9a146-1293-531e-bb02-0af7ad1b018e"