VIP impersonation with BEC language (near match, untrusted sender)

name: "VIP impersonation with BEC language (near match, untrusted sender)"
description: |
  Sender is using a display name that matches the display name of someone in your $org_vips list.

  Detects potential Business Email Compromise (BEC) attacks by analyzing text within email body from untrusted senders.
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any($org_vips,
          0 <= strings.ilevenshtein(sender.display_name, .display_name) < 4
  )
  and any(ml.nlu_classifier(body.current_thread.text).intents,
          .name == "bec" and .confidence in ("medium", "high")
  )
  and (
    (
      profile.by_sender().prevalence != "common"
      and not profile.by_sender().solicited
    )
    or (
      profile.by_sender().any_messages_malicious_or_spam
      and not profile.by_sender().any_messages_benign
    )
    or profile.by_sender().days_since.last_outbound > 365
  )
  // negate sharepoint notifications originating from within the org
  and not (
    sender.email.email in ('no-reply@sharepointonline.com')
    and length(headers.reply_to) > 0
    and all(headers.reply_to, .email.domain.root_domain 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_messages_benign
tags:
  - "Attack surface reduction"
attack_types:
  - "BEC/Fraud"
tactics_and_techniques:
  - "Impersonation: VIP"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Natural Language Understanding"
  - "Sender analysis"
id: "303081da-6850-5ba6-9589-c3dc7673320e"