sublimehighRule

Service abuse: DocSend share from newly registered domain

This Attack Surface Reduction (ASR) rule matches on DocSend notifications with recently registered reply-to domains.

MITRE ATT&CK

T1566.002 T1534 T1656 T1566 T1566.001 T1598 T1036 T1027 T1598.003

defense-evasioninitial-access

Detection Query

type.inbound

// Legitimate DocSend sending infratructure
and sender.email.email == "no-reply@docsend.com"
and headers.auth_summary.spf.pass
and headers.auth_summary.dmarc.pass

// the message needs to have a reply-to address
and length(headers.reply_to) > 0

// reply-to email address has never received an email from your org
and not any(headers.reply_to, .email.email in $recipient_emails)

// new reply-to
and any(headers.reply_to, network.whois(.email.domain).days_old < 30)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Tags

Attack surface reduction

Raw Content

name: "Service abuse: DocSend share from newly registered domain"
description: "This Attack Surface Reduction (ASR) rule matches on DocSend notifications with recently registered reply-to domains."
type: "rule"
severity: "high"
source: |
  type.inbound
  
  // Legitimate DocSend sending infratructure
  and sender.email.email == "no-reply@docsend.com"
  and headers.auth_summary.spf.pass
  and headers.auth_summary.dmarc.pass
  
  // the message needs to have a reply-to address
  and length(headers.reply_to) > 0
  
  // reply-to email address has never received an email from your org
  and not any(headers.reply_to, .email.email in $recipient_emails)
  
  // new reply-to
  and any(headers.reply_to, network.whois(.email.domain).days_old < 30)
tags:
 - "Attack surface reduction"
attack_types:
  - "BEC/Fraud"
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "Free file host"
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "Sender analysis"
id: "3bc152f2-6722-57be-b924-055c35fa1e60"