Suspicious message with unscannable Cloudflare link

name: "Suspicious message with unscannable Cloudflare link"
description: "This rule detects messages with unscannable links to cloudflare infrastructure with suspicious indicators in the subject or display name from an unsolicited sender."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and (
    (
      // few links
      0 < length(body.links) < 20
      // fewer unique root domain links
      and length(distinct(body.links, .href_url.domain.root_domain)) < 10
      // sender domain matches no body domains
      and all(body.links,
              .href_url.domain.root_domain != sender.email.domain.root_domain
      )
    )
    or beta.scan_qr(file.message_screenshot()).found
  )
  
  // negate bouncebacks and undeliverables
  and not any(attachments,
              .content_type in (
                "message/global-delivery-status",
                "message/delivery-status"
              )
  )
  
  // suspicious subject or display name
  and (
    regex.icontains(subject.subject,
                    "termination.*notice",
                    "38417",
                    ":completed",
                    "[il1]{2}mit.*ma[il1]{2} ?bo?x",
                    "[il][il][il]egai[ -]",
                    "[li][li][li]ega[li] attempt",
                    "[ng]-?[io]n .*block",
                    "[ng]-?[io]n .*cancel",
                    "[ng]-?[io]n .*deactiv",
                    "[ng]-?[io]n .*disabl",
                    "action.*required",
                    "abandon.*package",
                    "about.your.account",
                    "acc(ou)?n?t (is )?on ho[li]d",
                    "acc(ou)?n?t.*terminat",
                    "acc(oun)?t.*[il1]{2}mitation",
                    "access.*limitation",
                    "account (will be )?block",
                    "account.*de-?activat",
                    "account.*locked",
                    "account.*re-verification",
                    "account.*security",
                    "account.*suspension",
                    "account.has.been",
                    "account.has.expired",
                    "account.will.be.blocked",
                    "account v[il]o[li]at",
                    "activity.*acc(oun)?t",
                    "almost.full",
                    "app[li]e.[il]d",
                    "authenticate.*account",
                    "been.*suspend",
                    "clos.*of.*account.*processed",
                    "confirm.your.account",
                    "courier.*able",
                    "crediential.*notif",
                    "deactivation.*in.*progress",
                    "delivery.*attempt.*failed",
                    "document.received",
                    "documented.*shared.*with.*you",
                    "dropbox.*document",
                    "e-?ma[il1]+ .{010}suspen",
                    "e-?ma[il1]{1} user",
                    "e-?ma[il1]{2} acc",
                    "e-?ma[il1]{2}.*up.?grade",
                    "e.?ma[il1]{2}.*server",
                    "e.?ma[il1]{2}.*suspend",
                    "email.update",
                    "faxed you",
                    "fraud(ulent)?.*charge",
                    "from.helpdesk",
                    "fu[il1]{2}.*ma[il1]+[ -]?box",
                    "has.been.*suspended",
                    "has.been.limited",
                    "have.locked",
                    "he[li]p ?desk upgrade",
                    "heipdesk",
                    "i[il]iega[il]",
                    "ii[il]ega[il]",
                    "incoming e?mail",
                    "incoming.*fax",
                    "lock.*security",
                    "ma[il1]{1}[ -]?box.*quo",
                    "ma[il1]{2}[ -]?box.*fu[il1]",
                    "ma[il1]{2}box.*[il1]{2}mit",
                    "ma[il1]{2}box stor",
                    "mail on.?hold",
                    "mail.*box.*migration",
                    "mail.*de-?activat",
                    "mail.update.required",
                    "mails.*pending",
                    "messages.*pending",
                    "missed.*shipping.*notification",
                    "missed.shipment.notification",
                    "must.update.your.account",
                    "new [sl][io]g?[nig][ -]?in from",
                    "new voice ?-?mail",
                    "notifications.*pending",
                    "office.*3.*6.*5.*suspend",
                    "office365",
                    "on google docs with you",
                    "online doc",
                    "password.*compromised",
                    "periodic maintenance",
                    "potential(ly)? unauthorized",
                    "refund not approved",
                    "report",
                    "revised.*policy",
                    "scam",
                    "scanned.?invoice",
                    "secured?.update",
                    "security breach",
                    "securlty",
                    "signed.*delivery",
                    "statement is ready",
                    "status of your .{314}? ?delivery",
                    "susp[il1]+c[il1]+ous.*act[il1]+v[il1]+ty",
                    "suspicious.*sign.*[io]n",
                    "suspicious.activit",
                    "temporar(il)?y deactivate",
                    "temporar[il1]{2}y disab[li]ed",
                    "temporarily.*lock",
                    "un-?usua[li].activity",
                    "unable.*deliver",
                    "unauthorized.*activit",
                    "unauthorized.device",
                    "undelivered message",
                    "unread.*doc",
                    "unusual.activity",
                    "upgrade.*account",
                    "upgrade.notice",
                    "urgent message",
                    "urgent.verification",
                    "v[il1]o[li1]at[il1]on security",
                    "va[il1]{1}date.*ma[il1]{2}[ -]?box",
                    "verification ?-?require",
                    "verification( )?-?need",
                    "verify.your?.account",
                    "web ?-?ma[il1]{2}",
                    "web[ -]?ma[il1]{2}",
                    "will.be.suspended",
                    "your (customer )?account .as",
                    "your.office.365",
                    "your.online.access"
    )
    or any($suspicious_subjects, strings.icontains(subject.subject, .))
    or regex.icontains(sender.display_name,
                       "Admin",
                       "Administrator",
                       "Alert",
                       "Assistant",
                       "Billing",
                       "Benefits",
                       "Bonus",
                       "CEO",
                       "CFO",
                       "CIO",
                       "CTO",
                       "Chairman",
                       "Claim",
                       "Confirm",
                       "Critical",
                       "Customer Service",
                       "Deal",
                       "Discount",
                       "Director",
                       "Exclusive",
                       "Executive",
                       "Fax",
                       "Free",
                       "Gift",
                       "/bHR/b",
                       "Helpdesk",
                       "Human Resources",
                       "Immediate",
                       "Important",
                       "Info",
                       "Information",
                       "Invoice",
                       '\bIT\b',
                       "Legal",
                       "Lottery",
                       "Management",
                       "Manager",
                       "Member Services",
                       "Notification",
                       "Offer",
                       "Operations",
                       "Order",
                       "Partner",
                       "Payment",
                       "Payroll",
                       "President",
                       "Premium",
                       "Prize",
                       "Receipt",
                       "Refund",
                       "Registrar",
                       "Required",
                       "Reward",
                       "Sales",
                       "Secretary",
                       "Security",
                       "Service",
                       "Signature",
                       "SSA",
                       "Storage",
                       "Support",
                       "Sweepstakes",
                       "System",
                       "Tax",
                       "Tech Support",
                       "Update",
                       "Upgrade",
                       "Urgent",
                       "Validate",
                       "Verify",
                       "VIP",
                       "Webmaster",
                       "Winner",
    )
    or any(body.links, strings.ends_with(.href_url.url, ".exe"))
  )
  
  // link can't be scanned due to Cloudflare captcha
  and (
    any(body.links,
        (
          strings.icontains(ml.link_analysis(., mode="aggressive").final_dom.display_text,
                            "cloudflare"
          )
          // includes the turnstile CAPTCHA
          or (
            strings.icontains(ml.link_analysis(., mode="aggressive").final_dom.raw,
                              'https://challenges.cloudflare.com/turnstile/'
            )
            // has a short body length indicating the page is gated behind the turnstile instead
            // of just including the turnstile
            and length((
                         ml.link_analysis(., mode="aggressive").final_dom.display_text
                       )
            ) < 200
          )
        )
        and not (
          ( // a Cloudflare error page
            strings.ilike(ml.link_analysis(., mode="aggressive").final_dom.display_text,
                          "*error code*"
            )
            and any(ml.link_analysis(., mode="aggressive").final_dom.links,
                    strings.icontains(.href_url.query_params,
                                      "utm_source=errorcode"
                    )
            )
          ) // a cookie warning mentioning Cloudflare
          or regex.icontains(ml.link_analysis(., mode="aggressive").final_dom.display_text,
                             "cookie.{0,50}Cloudflare"
          )
          or ml.link_analysis(., mode="aggressive").effective_url.domain.root_domain in (
            "marketbeat.com"
          )
        )
    )
    or any(beta.scan_qr(file.message_screenshot()).items,
           .type == "url"
           and (
             strings.icontains(ml.link_analysis(.url, mode="aggressive").final_dom.display_text,
                               "cloudflare"
             )
             // includes the turnstile CAPTCHA
             or (
               strings.icontains(ml.link_analysis(.url, mode="aggressive").final_dom.raw,
                                 'https://challenges.cloudflare.com/turnstile/'
               )
               // has a short body length indicating the page is gated behind the turnstile instead
               // of just including the turnstile
               and length((
                            ml.link_analysis(.url, mode="aggressive").final_dom.display_text
                          )
               ) < 200
             )
           )
           and not (
             ( // a Cloudflare error page
               strings.ilike(ml.link_analysis(.url, mode="aggressive").final_dom.display_text,
                             "*error code*"
               )
               and any(ml.link_analysis(.url, mode="aggressive").final_dom.links,
                       strings.icontains(.href_url.query_params,
                                         "utm_source=errorcode"
                       )
               )
             ) // a cookie warning mentioning Cloudflare
             or regex.icontains(ml.link_analysis(.url, mode="aggressive").final_dom.display_text,
                                "cookie.{0,50}Cloudflare"
             )
             or ml.link_analysis(.url, mode="aggressive").effective_url.domain.root_domain in (
               "marketbeat.com"
             )
           )
    )
  )
  and (
    not profile.by_sender_email().solicited
    or (
      profile.by_sender().any_messages_malicious_or_spam
      and not profile.by_sender().any_messages_benign
    )
  )
  // 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
  )
  and not profile.by_sender().any_messages_benign

tags:
  - "Attack surface reduction"
attack_types:
  - "Credential Phishing"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "URL analysis"
  - "Sender analysis"
id: "70ea21f9-2a88-5e33-81a2-4f3384080a04"