Brand impersonation: Mailchimp

name: "Brand impersonation: Mailchimp"
description: "Detects messages from senders impersonating Mailchimp through display name spoofing or brand logo usage, combined with security-themed content and suspicious authentication patterns."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and (
    // display name contains Mailchimp
    (
      strings.ilike(strings.replace_confusables(sender.display_name),
                    '*mailchimp*'
      )
      // levenshtein distance similar to Mailchimp
      or strings.ilevenshtein(strings.replace_confusables(sender.display_name),
                              'mailchimp'
      ) <= 1
      or any(ml.logo_detect(file.message_screenshot()).brands,
             .name == "MailChimp" and .confidence == "high"
      )
    )
  )
  and (
    any(ml.nlu_classifier(body.current_thread.text).topics,
        .name in (
          "Security and Authentication",
          "Secure Message",
          "Reminders and Notifications"
        )
        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"
           )
           and .confidence in ("medium", "high")
           and beta.ocr(file.message_screenshot()).text != ""
    )
    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"
    )
  )
  
  // and the sender is not in org_domains or from Mailchimp domains and passes auth
  and not (
    sender.email.domain.root_domain in $org_domains
    or (
      sender.email.domain.root_domain in ("intuit.com", "mailchimp.com")
      and headers.auth_summary.dmarc.pass
    )
  )
  and not strings.ends_with(headers.message_id, ".mailchimp.com>")
  // and the sender is not from high trust sender root domains
  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:
  - "Credential Phishing"
tactics_and_techniques:
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Computer Vision"
  - "Natural Language Understanding"
  - "Content analysis"
  - "Header analysis"
  - "Sender analysis"
id: "48b454c7-fcd7-54d4-b460-5dfec2c1a3e2"