Sublime Security medium experimental mql

BEC/Fraud: Reply-chain manipulation with urgent keywords and self-reply

Detects suspicious reply messages with urgent language in sender name or email address, minimal body content, and the sender's email address appearing in previous thread content, indicating a self reply.

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Detection Logic

type.inbound
and subject.is_reply
and length(attachments) == 0
// short current thread
and length(body.current_thread.text) < 25
// only 1 previous thread
and length(body.previous_threads) == 1
and any(recipients.to,
        .email.domain.root_domain != sender.email.domain.root_domain
)
// urgent or authority based keywords in sender display name or local part
and (
  regex.icontains(sender.display_name,
                  '\b(?:(?:crucial
| urgent
| immediate
| important
| quick)(?:ly)?
| immediatetask
| emergency)\b'
  )
  or regex.icontains(sender.email.local_part, '(?:task
| ceo
| executive)')
)
// sender replied to themselves
and any(body.previous_threads, strings.icontains(.preamble, sender.email.email))

Field Validations

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