Link: Multistage landing - Abused Docusign

name: "Link: Multistage landing - Abused Docusign"
description: "The detection rule matches on message groups which make use of Docusign as a landing page. The landing page contains links which are newly registered, use free file or subdomain hosts, url shortners or when visited are phishing pages, lead to a captcha or rediret to a top website."
type: "rule"
severity: "high"
source: |
  type.inbound
  
  //
  // 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
  
  // message is from docusign actual
  and sender.email.domain.root_domain == 'docusign.net'
  and (headers.auth_summary.spf.pass or headers.auth_summary.dmarc.pass)
  
  // filter out all the links, keeping only the links of interest
  and any(filter(body.links,
                 // target the DocuSign link
                 (
                   regex.icontains(.display_text,
                                   "((view|show).completed.document|(?:re)?view doc|view.attached)"
                   )
                   or strings.icontains(.href_url.url, '/Signing/EmailStart.aspx')
                   or strings.icontains(.href_url.url, '/signing/emails/v')
                 )
          ),
  
          // filter down the links on the docusign page to those that are external to docusign
          any(filter(ml.link_analysis(., mode="aggressive").final_dom.links,
                     .href_url.domain.root_domain != 'docusign.net'
                     and .href_url.domain.root_domain != 'docusign.com'
                     and .href_url.domain.root_domain not in $org_domains
                     // relative links (no domains)
                     and .href_url.domain.domain is not null
              ),
              (
                // any of those links domains are new
                network.whois(.href_url.domain).days_old < 30
                // go to free file hosts
                or .href_url.domain.root_domain in $free_file_hosts
                or .href_url.domain.domain in $free_file_hosts
  
                // go to free subdomains hosts
                or (
                  .href_url.domain.root_domain in $free_subdomain_hosts
                  // where there is a subdomain
                  and .href_url.domain.subdomain is not null
                  and .href_url.domain.subdomain != "www"
                )
                // go to url shortners
                or .href_url.domain.root_domain in $url_shorteners
                or .href_url.domain.root_domain in $social_landing_hosts
                or .href_url.domain.domain in $url_shorteners
                or .href_url.domain.domain in $social_landing_hosts
                or (
                  // find any links that mention common "action" words
                  regex.icontains(.display_text,
                                  '(?:view|click|show|access|download|goto|Validate|Va[il]idar|login|verify|account)'
                  )
                  and (
                    // and when visiting those links, are phishing
                    ml.link_analysis(., mode="aggressive").credphish.disposition == "phishing"
  
                    // hit a captcha page
                    or ml.link_analysis(., mode="aggressive").credphish.contains_captcha
  
                    // or the page redirects to common website, observed when evasion happens
                    or (
                      length(ml.link_analysis(., mode="aggressive").redirect_history
                      ) > 0
                      and ml.link_analysis(., mode="aggressive").effective_url.domain.root_domain in $tranco_10k
                    )
                  )
                )
              )
          )
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "Free subdomain host"
  - "Free file host"
detection_methods:
  - "Content analysis"
  - "Sender analysis"
  - "URL analysis"
  - "Whois"
  - "HTML analysis"
id: "4189a645-04a5-5bdb-bf00-031442ced292"