sublimemediumRule

Attachment: DocuSign impersonation via PDF linking to new domain

This rule detects PDF files containing a DocuSign logo linking to a newly created domain (Less than or equal to 3 days)

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1598.003

initial-access

Detection Query

type.inbound
and any(attachments,
        .file_type == "pdf"
        and any(ml.logo_detect(.).brands, .name == "DocuSign")
        and any(file.explode(.),
                any(.scan.pdf.urls, network.whois(.domain).days_old <= 3)
        )
)

// negate highly trusted sender domains unless they fail DMARC authentication
and (
  (
    sender.email.domain.root_domain in $high_trust_sender_root_domains
    and not headers.auth_summary.dmarc.pass
  )
  or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)

// excludes senders that contain "via" in the display name a resilient way
and not (
  any(headers.hops,
      any(.fields,
          .name == "X-Api-Host" and strings.ends_with(.value, "docusign.net")
      )
  )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: DocuSign impersonation via PDF linking to new domain"
description: "This rule detects PDF files containing a DocuSign logo linking to a newly created domain (Less than or equal to 3 days)"
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(attachments,
          .file_type == "pdf"
          and any(ml.logo_detect(.).brands, .name == "DocuSign")
          and any(file.explode(.),
                  any(.scan.pdf.urls, network.whois(.domain).days_old <= 3)
          )
  )
  
  // negate highly trusted sender domains unless they fail DMARC authentication
  and (
    (
      sender.email.domain.root_domain in $high_trust_sender_root_domains
      and not headers.auth_summary.dmarc.pass
    )
    or sender.email.domain.root_domain not in $high_trust_sender_root_domains
  )
  
  // excludes senders that contain "via" in the display name a resilient way
  and not (
    any(headers.hops,
        any(.fields,
            .name == "X-Api-Host" and strings.ends_with(.value, "docusign.net")
        )
    )
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Impersonation: Brand"
  - "PDF"
  - "Social engineering"
detection_methods:
  - "Header analysis"
  - "Sender analysis"
  - "URL analysis"
  - "File analysis"
  - "Computer Vision"
  - "Whois"
id: "f0c96282-6eb9-5e84-aa9d-a48f66db5a74"