• Sublime Core Feed
Medium Severity

Suspicious attachment with unscannable Cloudflare link

Labels

Credential Phishing
Evasion
PDF
Social engineering
Impersonation: Employee
Impersonation: VIP
File analysis
URL analysis
Sender analysis
Content analysis
Header analysis
Natural Language Understanding

Description

A PDF or Office document contains suspicious URLs that lead to Cloudflare-protected pages with turnstile CAPTCHA gates. The sender uses deceptive display names and subjects indicating urgency or authority.

References

No references.

Sublime Security
Created Jun 2nd, 2025 • Last updated Jul 16th, 2025
Feed Source
Sublime Core Feed
Source
GitHub
type.inbound
and any(attachments,
        (
          .file_extension in $file_extensions_macros
          or .file_extension == "pdf"
          or .file_type in ("pdf", "doc", "docx", "xls", "xlsx")
          or .content_type in ("application/pdf")
        )
        and any(file.explode(.),
                // few links
                0 < length(.scan.url.urls) < 20
                // fewer unique root domain links
                and length(distinct(.scan.url.urls, .domain.root_domain)) < 10
                // sender domain matches no body domains
                and all(.scan.url.urls,
                        .domain.root_domain != sender.email.domain.root_domain
                )
        )
)

// 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?\.gov',
                     "Storage",
                     "Support",
                     "Sweepstakes",
                     "System",
                     "Tax",
                     "Tech Support",
                     "Update",
                     "Upgrade",
                     "Urgent",
                     "Validate",
                     "Verify",
                     "VIP",
                     "Webmaster",
                     "Winner",
  )
  or any(attachments,
         (
           .file_extension in $file_extensions_macros
           or .file_extension == "pdf"
           or .file_type in ("pdf", "doc", "docx", "xls", "xlsx")
           or .content_type in ("application/pdf")
         )
         and any(file.explode(.),
                 any(.scan.url.urls, strings.ends_with(.url, ".exe"))
                 or any(ml.nlu_classifier(.scan.ocr.raw).intents, .name == "cred_theft")
         )
  )
)
and any(attachments,
        (
          .file_extension in $file_extensions_macros
          or .file_extension == "pdf"
          or .file_type in ("pdf", "doc", "docx", "xls", "xlsx")
          or .content_type in ("application/pdf")
        )
        and any(file.explode(.),
                any(.scan.url.urls,
                    (
                      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"
                      )
                    )
                )
        )
)

and (
  not profile.by_sender().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
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