• Sublime Core Feed
Medium Severity

Domain impersonation: Freemail reply-to local lookalike with financial request

Description

This technique takes advantage of the use of free email services for the reply-to address. By incorporating the sender domain in the local part of the reply-to address, the attacker creates a visually similar appearance to a legitimate email address.

References

No references.

Sublime Security
Created Aug 17th, 2023 • Last updated Aug 5th, 2025
Source
type.inbound
and any(headers.reply_to,
        .email.email != sender.email.email
        and .email.domain.domain in $free_email_providers
        and .email.email not in $sender_emails
        and strings.contains(.email.local_part, sender.email.domain.sld)
)
and (
  any(ml.nlu_classifier(body.current_thread.text).intents, .name == "bec" and .confidence in ("medium", "high"))
      or (
        any(ml.nlu_classifier(body.current_thread.text).entities, .name == "financial")
        and any(ml.nlu_classifier(body.current_thread.text).entities, .name == "request")
        and any(ml.nlu_classifier(body.current_thread.text).entities, .name == "urgency")
        and any(ml.nlu_classifier(body.current_thread.text).entities, .name == "sender")
        and any(ml.nlu_classifier(body.current_thread.text).intents, .name != "benign")
      )
)
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