sublimemediumRule

Link: Squarespace infrastructure abuse

Detects inbound messages containing exactly one Squarespace tracking link but lacking authentic Squarespace email headers and sender patterns.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1598.003

initial-access

Detection Query

type.inbound
and any(body.links, .href_url.domain.domain == "engage.squarespace-mail.com")
and length(body.links) < 10
// there is one unique Squarespace Link in the message
and length(distinct(filter(body.links,
                           .href_url.domain.domain == "engage.squarespace-mail.com"
                    ),
                    .href_url.url
           )
) == 1
and not headers.return_path.domain.root_domain == "squarespace-mail.com"
and not any(headers.domains, .root_domain == "squarespace-mail.com")
and profile.by_sender_email().prevalence != "common"

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Link: Squarespace infrastructure abuse"
description: "Detects inbound messages containing exactly one Squarespace tracking link but lacking authentic Squarespace email headers and sender patterns."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(body.links, .href_url.domain.domain == "engage.squarespace-mail.com")
  and length(body.links) < 10
  // there is one unique Squarespace Link in the message
  and length(distinct(filter(body.links,
                             .href_url.domain.domain == "engage.squarespace-mail.com"
                      ),
                      .href_url.url
             )
  ) == 1
  and not headers.return_path.domain.root_domain == "squarespace-mail.com"
  and not any(headers.domains, .root_domain == "squarespace-mail.com")
  and profile.by_sender_email().prevalence != "common"

attack_types:
  - "Credential Phishing"
  - "Spam"
tactics_and_techniques:
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Header analysis"
  - "URL analysis"
  - "Sender analysis"
id: "a8fe9d30-e64e-50e8-95d8-720e90676409"