Service abuse: Dropbox share from new domain

name: "Service abuse: Dropbox share from new domain"
description: "This Attack Surface Reduction (ASR) rule matches on Dropbox notifications with recently registered reply-to domains."
type: "rule"
severity: "medium"
source: |
  type.inbound
  
  //  Dropbox actual sending infrastructure
  and sender.email.email == "no-reply@dropbox.com"
  and headers.auth_summary.spf.pass
  and headers.auth_summary.dmarc.pass
  and strings.ends_with(headers.auth_summary.spf.details.designator,
                        '.dropbox.com'
  )
  
  // the message needs to have a reply-to address
  and length(headers.reply_to) > 0
  
  // 
  // 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
  // 
  
  // reply-to email address has never been sent an email by the org
  and not beta.profile.by_reply_to().solicited
  
  // do not match if the reply_to address has been observed as a reply_to address
  // of a message that has been classified as benign
  and not beta.profile.by_reply_to().any_messages_benign
  
  // new reply-to domain
  and any(headers.reply_to, network.whois(.email.domain).days_old < 30)
tags:
 - "Attack surface reduction"
attack_types:
  - "Callback Phishing"
  - "Credential Phishing"
  - "BEC/Fraud"
tactics_and_techniques:
  - "Evasion"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Sender analysis"
  - "Header analysis"
id: "0e664bd9-c3dd-53ca-a912-bb1a627e22ae"