• Sublime Core Feed
Medium Severity

Suspicious subject with long procedurally generated text blob

Description

This rule identifies subjects containing long strings of nonsensical or procedurally generated characters, which are often used in phishing or spam campaigns for campaign tracking and identification, as well as to bypass detection filters.

References

No references.

Sublime Security
Created Mar 12th, 2025 • Last updated Jan 12th, 2026
Source
type.inbound
// "#" symbol, and then letters, numbers or more symbols (-#)
and regex.imatch(subject.subject, ".*#[a-z0-9-#]+$")
// not JUST letters
and not regex.imatch(subject.subject, ".*#[a-z-]+$")
// not JUST numbers
and not regex.imatch(subject.subject, ".*#[0-9-]+$")
and not any(beta.ml_topic(body.current_thread.text).topics,
            .name in (
              "Professional and Career Development",
              "Reminders and Notifications"
            )
            and .confidence == "high"
)

// and 1 other suspicious element
and 2 of (
  any(recipients.to, strings.icontains(sender.display_name, .email.domain.sld)),
  (
    regex.imatch(sender.display_name, ".*#[a-z0-9-#]+$")
    and not regex.imatch(subject.subject, ".*#[a-z-]+$")
    and not regex.imatch(subject.subject, ".*#[0-9-]+$")
  ),
  any(ml.nlu_classifier(subject.subject).intents,
      .name == "cred_theft" and .confidence == "high"
  ),
  body.current_thread.text is null
)

// standard negations
and not profile.by_sender_email().any_messages_benign
and not profile.by_sender_email().solicited
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
)
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