• Sublime Core Feed
Medium Severity

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.

References

No references.

Sublime Security
Created Nov 28th, 2023 • Last updated Dec 12th, 2025
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
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