Open redirect: embluemail.com

name: "Open redirect: embluemail.com"
description: |
  Message contains use of the embluemail.com redirect. This has been exploited in the wild.
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(body.links,
          .href_url.domain.domain == "nts.embluemail.com"
          and strings.istarts_with(.href_url.path, '/p/cl')
          and strings.icontains(.href_url.query_params, '!')
          and regex.icontains(.href_url.query_params,
                              '\!(?:((?:%68|h)(?:%74|t){2}(?:%70|p)(?:%73|s)?)?(?:%3a|:))?(?:%2f|\/){2}'
          )
  )
  and not sender.email.domain.domain == "nts.embluemail.com"
  and not strings.iends_with(headers.message_id, '@embluemail.com>')
  
  // 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:
  - "Credential Phishing"
  - "Malware/Ransomware"
tactics_and_techniques:
  - "Open redirect"
detection_methods:
  - "Sender analysis"
  - "URL analysis"
id: "48c5abd3-4f3f-5a3f-8bc0-cbba10d901e6"