Attachment: ICS voicemail lure with suspicious link

name: "Attachment: ICS voicemail lure with suspicious link"
description: "Detects inbound emails containing an ICS calendar attachment whose event description mimics a voicemail notification (e.g., 'new voicemail', 'listen to your voicemail') and includes a link pointing to a free file hosting service, self-service creation platform, URL shortener, suspicious TLD, or a domain registered within the last 90 days. Excludes messages from high-trust sender domains that pass DMARC authentication."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(attachments,
          (
            .file_type == "ics"
            or .file_extension == "ics"
            or .content_type in ("application/ics", "text/calendar")
          )
          //
          // This rule makes use of a beta feature and is subject to change without notice
          // using the beta feature in custom rules is not suggested until it has been formally released
          //
          and any(beta.file.parse_ics(.).events,
                  // voicemail key words
                  regex.icontains(.description,
                                  'new voice\s?mail|voice\s?mail.{0,20}(?:notification|received|awaits|ready|logged)|listen\s+to\s+(?:your\s+)?voice\s?mail|you\s+(?:have|received)\s+a\s+new\s+voice|voice\s+message.{0,20}(?:notification|from your inbox|in your)'
                  )
                  // sus link
                  and any(.links,
                          .href_url.domain.root_domain in $free_file_hosts
                          or .href_url.domain.domain in $free_file_hosts
                          or .href_url.domain.root_domain in $self_service_creation_platform_domains
                          or .href_url.domain.domain in $self_service_creation_platform_domains
                          or .href_url.domain.tld in $suspicious_tlds
                          or .href_url.domain.domain in $url_shorteners
                          or .href_url.domain.root_domain in $url_shorteners
                          or network.whois(.href_url.domain).days_old < 90
                  )
          )
  )
  and not (
    sender.email.domain.root_domain in $high_trust_sender_root_domains
    and coalesce(headers.auth_summary.dmarc.pass, false)
  )
attack_types:
  - "ICS Phishing"
  - "Credential Phishing"
tactics_and_techniques:
  - "Social engineering"
  - "Free file host"
  - "Evasion"
detection_methods:
  - "File analysis"
  - "Content analysis"
  - "URL analysis"
  - "Whois"
  - "Header analysis"
id: "ef6082ce-1073-570e-b04d-abac1652ec82"