Business Email Compromise (BEC) attempt from untrusted sender (French/Français)

name: "Business Email Compromise (BEC) attempt from untrusted sender (French/Français)"
description: "Detects potential Business Email Compromise (BEC) attacks by searching for common French BEC language within the email body from first-time senders."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and length(body.links) == 0
  and ml.nlu_classifier(body.current_thread.text).language == "french"
  and 1 of (
    regex.icontains(subject.subject,
                    '(mise (a|à) jour|changé|changement).{0,20}(bancaire|de banque)'
    ),
    regex.icontains(body.current_thread.text,
                    '(changement|changé) de (banque)|changement bancaire|coordonnées.{0,20}(compte|banque|bancaire|salaire)',
    ),
    (regex.icontains(body.current_thread.text, 'parler.{0,20}confiance'))
  )
  // negating legit replies
  and not (
    (
      strings.istarts_with(subject.subject, "RE:")
      // out of office auto-reply
      // the NLU model will handle these better natively soon
      or strings.istarts_with(subject.subject, "Automatic reply:")
      or regex.imatch(subject.subject,
                      '(\[[^\]]+\]\s?){0,3}(re|fwd?|automat.*)\s?:.*'
      )
    )
    and (
      length(headers.references) > 0
      or any(headers.hops, any(.fields, strings.ilike(.name, "In-Reply-To")))
    )
  )
  and (
    not profile.by_sender().solicited
    or (
      profile.by_sender().any_messages_malicious_or_spam
      and not profile.by_sender().any_messages_benign
    )
  )
  
  // 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
  )

attack_types:
  - "BEC/Fraud"
tactics_and_techniques:
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "Sender analysis"
id: "b7d1e096-d9cc-5a79-9753-5d9565794433"