sublimehighRule

Link: Observed URL pattern with specific domain registrar

Detects messages using Element Email service infrastructure, identified by characteristic URL patterns with /f/ paths, unsubscribe links, single domain usage, and Cloudflare domain registration. This pattern indicates potential abuse of legitimate email marketing services.

MITRE ATT&CK

T1566

Detection Query

type.inbound
// Signs of Email Element use
// all links are the same domain
and length(distinct(body.current_thread.links, .href_url.domain.root_domain)) == 1
// all links contain the /f/
and all(body.current_thread.links,
        regex.icontains(.href_url.path, '^/(?:unsubscribe/)?f/')
)
// there is an unsub link
and length(filter(body.current_thread.links,
                  strings.icontains(.href_url.path, '/unsubscribe/f/')
           )
) == 1
// this actor uses CF for domain management
and network.whois(sender.email.domain).registrar_name == "Cloudflare, Inc."

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Link: Observed URL pattern with specific domain registrar"
description: "Detects messages using Element Email service infrastructure, identified by characteristic URL patterns with /f/ paths, unsubscribe links, single domain usage, and Cloudflare domain registration. This pattern indicates potential abuse of legitimate email marketing services."
type: "rule"
severity: "high"
source: |
  type.inbound
  // Signs of Email Element use
  // all links are the same domain
  and length(distinct(body.current_thread.links, .href_url.domain.root_domain)) == 1
  // all links contain the /f/
  and all(body.current_thread.links,
          regex.icontains(.href_url.path, '^/(?:unsubscribe/)?f/')
  )
  // there is an unsub link
  and length(filter(body.current_thread.links,
                    strings.icontains(.href_url.path, '/unsubscribe/f/')
             )
  ) == 1
  // this actor uses CF for domain management
  and network.whois(sender.email.domain).registrar_name == "Cloudflare, Inc."
attack_types:
  - "Spam"
tactics_and_techniques:
  - "Free email provider"
detection_methods:
  - "URL analysis"
  - "Sender analysis"
  - "Whois"
id: "82ee7653-deb3-533a-941a-59d047be9b5c"