Cyrillic vowel substitutions with suspicious subject from unknown sender

name: "Cyrillic vowel substitutions with suspicious subject from unknown sender"
description: "This rule detects unsolicited messages with between 1-9 links containing a suspicious subject as well as Cyrillic vowel substitutions detected in either the subject or the senders display name."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and 0 < length(body.links) < 10
  
  //  display name or subject contains confusable vowels
  and any([subject.subject, sender.display_name],
          regex.icontains(., '(а|е|и|о|у)')
  )
  
  // and suspicious subject
  and regex.icontains(subject.subject,
                      // https://github.com/sublime-security/static-files/blob/main/suspicious_subjects_regex.txt
                      "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",
                      "revised.*policy",
                      "scam",
                      "scanned.?invoice",
                      "secured?.update",
                      "security breach",
                      "securlty",
                      "signed.*delivery",
                      "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",
                      "unauthorized.sign.?in",
                      "unrecognized.*activit",
                      "unrecognized.sign.?in",
                      "unrecognized.*activit",
                      "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",
  
                      // https://github.com/sublime-security/static-files/blob/main/suspicious_subjects.txt
                      "account has been limited",
                      "action required",
                      "almost full",
                      "apd notifi cation",
                      "are you at your desk",
                      "are you available",
                      "attached file to docusign",
                      "banking is temporarily unavailable",
                      "bankofamerica",
                      "closing statement invoice",
                      "completed: docusign",
                      "de-activation of",
                      "delivery attempt",
                      "delivery stopped for shipment",
                      "detected suspicious",
                      "detected suspicious actvity",
                      "docu sign",
                      "document for you",
                      "document has been sent to you via docusign",
                      "document is ready for signature",
                      "docusign",
                      "encrypted message",
                      "failed delivery",
                      "fedex tracking",
                      "file was shared",
                      "freefax",
                      "fwd: due invoice paid",
                      "has shared",
                      "inbox is full",
                      "invitation to comment",
                      "invitation to edit",
                      "invoice due",
                      "left you a message",
                      "message from",
                      "new message",
                      "new voicemail",
                      "on desk",
                      "out of space",
                      "password reset",
                      "payment status",
                      "quick reply",
                      "re: w-2",
                      "required",
                      "required: completed docusign",
                      "ringcentral",
                      "scanned image",
                      "secured files",
                      "secured pdf",
                      "security alert",
                      "new sign-in",
                      "new sign in",
                      "sign-in attempt",
                      "sign in attempt",
                      "staff review",
                      "suspicious activity",
                      "unrecognized login attempt",
                      "upgrade immediately",
                      "urgent",
                      "wants to share",
                      "w2",
                      "you have notifications pending",
                      "your account",
                      "your amazon order",
                      "your document settlement",
                      "your order with amazon",
                      "your password has been compromised",
  )
  
  // the message is unsolicited and no false positives
  and (
    not profile.by_sender().solicited
    or (
      length(headers.reply_to) > 0
      and all(headers.reply_to, .email.email not in $recipient_emails)
    )
  )
  and not profile.by_sender().any_messages_benign
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Sender analysis"
id: "10251c3c-b926-5742-9417-4cf58d182230"