Brand impersonation: SendGrid

name: "Brand impersonation: SendGrid"
description: "Detects inbound messages that impersonate Twilio/SendGrid through display name or domain manipulation, combined with security or authentication-themed content, while failing authentication checks and originating from untrusted sources."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and (
    (
      // SendGrid impersonation patterns
      strings.ilike(strings.replace_confusables(sender.display_name),
                    '*sendgrid*'
      )
      or strings.ilevenshtein(strings.replace_confusables(sender.display_name),
                              'sendgrid'
      ) <= 1
      or (
        strings.ilike(strings.replace_confusables(sender.email.local_part),
                      '*sendgrid*'
        )
        and (
          sender.display_name is null
          or strings.ilike(strings.replace_confusables(subject.base),
                           '*sendgrid*'
          )
        )
      )
      or any(ml.logo_detect(file.message_screenshot()).brands,
             .name == "SendGrid" and .confidence == "high"
      )
    )
    or (
      // Twilio impersonation patterns
      strings.ilike(strings.replace_confusables(sender.display_name), '*twilio*')
      or strings.ilevenshtein(strings.replace_confusables(sender.display_name),
                              'twilio'
      ) <= 1
      or (
        strings.ilike(strings.replace_confusables(sender.email.local_part),
                      '*twilio*'
        )
        and (
          sender.display_name is null
          or strings.ilike(strings.replace_confusables(subject.base), '*twilio*')
        )
      )
    )
    or strings.icontains(body.current_thread.text, "the sendgrid team")
    or 2 of (
      regex.icontains(body.current_thread.text, '(?:Twilio|SendGrid)'),
      strings.icontains(body.current_thread.text, '1801 California St'),
      strings.icontains(body.current_thread.text, 'Denver, CO 80202')
    )
    // SendGrid content from non-SendGrid marketing platforms
    or (
      sender.email.domain.root_domain in (
        "selfcast.com",
        "mailchimp.com",
        "constantcontact.com",
        "hubspot.com",
        "klaviyo.com",
        "mailgun.com"
      )
      and (
        (
          (
            strings.icontains(body.current_thread.text, "sendgrid")
            or strings.icontains(subject.base, "sendgrid")
          )
          and 3 of (
            strings.icontains(body.current_thread.text, "webhook"),
            strings.icontains(body.current_thread.text, "endpoint"),
            strings.icontains(body.current_thread.text, "api"),
            strings.icontains(body.current_thread.text, "delivery"),
            strings.icontains(body.current_thread.text, "event notification")
          )
        )
        and (
          // Look for SendGrid-related content with non-SendGrid tracking links
          any(body.links,
              strings.icontains(.href_url.url, "selfcast.com")
              or (
                .display_url.url is not null
                and strings.icontains(.display_url.url, "sendgrid.com")
              )
          )
        )
      )
    )
  )
  and (
    // Content analysis using ML/NLU
    any(ml.nlu_classifier(body.current_thread.text).topics,
        .name in (
          "Security and Authentication",
          "Secure Message",
          "Reminders and Notifications",
          "Software and App Updates",
          "Customer Service and Support"
        )
        and .confidence in ("medium", "high")
    )
    or any(ml.nlu_classifier(beta.ocr(file.message_screenshot()).text).topics,
           .name in (
             "Security and Authentication",
             "Secure Message",
             "Reminders and Notifications",
             "Software and App Updates",
             "Customer Service and Support"
           )
           and .confidence in ("medium", "high")
    )
    or any(ml.nlu_classifier(body.current_thread.text).intents,
           .name == "cred_theft" and .confidence == "high"
    )
    or any(ml.nlu_classifier(beta.ocr(file.message_screenshot()).text).intents,
           .name == "cred_theft" and .confidence == "high"
    )
  
    // any capacity or limits mentioned
    or any([subject.base, body.current_thread.text],
           (strings.icontains(., "capacity") or strings.icontains(., "limit"))
           and regex.icontains(., '\breach(?:\b|ed)')
    )
  )
  
  // and the sender is not in org_domains or from sendgrid domains and passes auth
  and not (
    sender.email.domain.valid
    and (
      sender.email.domain.root_domain in $org_domains
      or (
        sender.email.domain.root_domain in (
          "sendgrid.com",
          "sendgrid.net",
          "twilio.com",
          "swoogo.com", // events planning software used by Twillio
          "sendsafely.com", // secure delivery used by Twillio
          "evolve.com", // same address as Twillio
          "sendgridsolutions.com"
        )
      )
    )
    and headers.auth_summary.dmarc.pass
  )
  // Exclude high trust domains with valid auth and solicited senders
  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
  )
  and not profile.by_sender().solicited
attack_types:
  - "BEC/Fraud"
  - "Credential Phishing"
  - "Spam"
tactics_and_techniques:
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "Natural Language Understanding"
  - "Optical Character Recognition"
  - "Sender analysis"
id: "d800124f-6aa4-58e1-8fa7-beec4958924f"