Employee impersonation: Payroll fraud

name: "Employee impersonation: Payroll fraud"
description: |
  This rule detects messages impersonating employees, from unsolicited senders attempting to reroute payroll
  or alter payment details.
type: "rule"
severity: "high"
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 length(attachments) == 0
  and length(body.links) < 10
  and length(body.current_thread.text) < 800
  and (
    sender.email.domain.root_domain not in $org_domains
    or sender.email.domain.root_domain in $free_email_providers
  )
  and 1 of (
    regex.icontains(body.current_thread.text,
                    '(pay\s?(roll|check|date|day)|direct deposit|(acct|account) rephrase|paid.{0,50}problems|\bACH\b|\bdd\b|gehalt|salario|salary)'
    ),
    regex.icontains(subject.subject,
                    '(pay\s?(roll|check|date|day)|direct deposit|(acct|account) rephrase|paid.{0,50}problems|\bACH\b|\bdd\b|gehalt|salario|salary)'
    )
  )
  and (
    not profile.by_sender_email().solicited
    or (
      profile.by_sender().any_messages_malicious_or_spam
      and not profile.by_sender().any_messages_benign
    )
  )
  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 (
        any(distinct(headers.hops, .authentication_results.dmarc is not null),
            strings.ilike(.authentication_results.dmarc, "*fail")
        )
      )
    )
    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
  )

attack_types:
  - "BEC/Fraud"
tactics_and_techniques:
  - "Impersonation: Employee"
  - "Free email provider"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Sender analysis"
id: "2beb7d85-dfe3-5ecc-9b2a-d7416a3ef992"