Open redirect: fenc.com

name: "Open redirect: fenc.com"
description: |
  Message contains use of the fenc.com open redirect. This has been exploited in the wild.
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(body.links,
          .href_url.domain.root_domain == "fenc.com"
          and .href_url.path =~ "/redirector.aspx"
          and regex.icontains(.href_url.query_params,
                              'y=(?:https?|(?:\/|%2f)(?:\/|%2f))'
          )
          and not regex.icontains(.href_url.query_params, 'y=[^\&]*fenc\.com')
  )
  and not sender.email.domain.root_domain == "fenc.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: "6ff1ab52-70e2-5135-8715-a3b1cc57e10f"