Brand impersonation: Dropbox

name: "Brand impersonation: Dropbox"
description: |
  Impersonation of Dropbox, a file sharing service.
type: "rule"
severity: "medium"
source: |
  type.inbound
  and (
    strings.ilike(sender.display_name, '*dropbox*')
    or strings.ilevenshtein(sender.display_name, 'dropbox') <= 1
    or strings.ilike(sender.email.domain.domain, '*dropbox*')
    or any(body.links,
           .display_url.domain.root_domain == "dropbox.com"
           and .mismatched
           and not .href_url.domain.root_domain in (
             "mimecast.com",
             "mimecastprotect.com"
           )
    )
    or regex.icontains(body.current_thread.text,
                       'invited you to view the file ".*" on Dropbox',
                       'dr[o0]pb[o0]x.{0,20}share.{0,20}f[i1|][i1|l]es?',
                       'dropbox sign (?:account|team)'
    )
    // dropbox style button
    or length(html.xpath(body.html,
                         "//a[contains(@style, 'background-color: #0070e0') and contains(@style, 'color: white') and contains(@style, 'width: 210px')  and contains(@style, 'max-width: 210px') and contains(@style, 'border-radius: 4px') and contains(@style, 'text-align: center') and contains(@style, 'font-size: 15px')]"
              ).nodes
    ) == 1
  )
  and sender.email.domain.root_domain not in~ (
    'dropbox.com',
    'dropboxforum.com',
    'dropboxsign.com'
  )
  and (
    any(attachments,
        .file_type in $file_types_images
        and any(file.explode(.), strings.ilike(.scan.ocr.raw, "*dropbox*"))
    )
    or any(body.links,
           (
             (
               strings.ilike(.display_text,
                             "*review*",
                             "*sign*",
                             "*view*",
                             "*completed document*",
                             "*open agreement*",
                             "*open document*",
                             "*open file*"
               )
               and not strings.ilike(.display_text, "*view this email in*")
             )
             or (
               .display_text is null
               and .href_url.domain.root_domain in $free_file_hosts
             )
           )
           and (
             .href_url.domain.root_domain != "dropbox.com"
             and any(ml.nlu_classifier(body.current_thread.text).intents,
                     .name == "cred_theft" and .confidence in ("medium", "high")
             )
           )
    )
    or (
      length(ml.logo_detect(file.message_screenshot()).brands) != 0
      and all(ml.logo_detect(file.message_screenshot()).brands,
              .name == "Dropbox"
      )
    )
  )
  and sender.email.email not in $recipient_emails
  
  // negate dropbox fax (aka hellofax)
  and not sender.email.domain.root_domain == 'hellofax.com'
  
  // negate iCloud Private Message Relay
  and not (
    sender.email.domain.domain == "privaterelay.appleid.com"
    or any(headers.hops, any(.fields, .name == "X-ICLOUD-HME"))
  )
  
  // 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
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "File analysis"
  - "Header analysis"
  - "Sender analysis"
id: "61f11d12-7033-53c9-a95a-df982ff31c4b"