sublimelowRule

Link: Free file host from freemail sender with NLU intent

Detects free file host links sent by freemail senders with a short body and NLU indicators.

MITRE ATT&CK

initial-access

Detection Query

type.inbound

// short body
and length(body.current_thread.text) < 500

// NLU intent
and (
  any(ml.nlu_classifier(body.current_thread.text).intents, .name != "benign")
  and length(ml.nlu_classifier(body.current_thread.text).intents) > 0
)

// free file host link
and any(body.links,
        .href_url.domain.domain in $free_file_hosts
        or .href_url.domain.root_domain in $free_file_hosts
)

// freemail sender
and sender.email.domain.root_domain in $free_email_providers
and (
  not profile.by_sender().any_false_positives
  and not profile.by_sender().solicited
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Tags

Attack surface reduction

Raw Content

name: "Link: Free file host from freemail sender with NLU intent"
description: "Detects free file host links sent by freemail senders with a short body and NLU indicators."
type: "rule"
severity: "low"
source: |
  type.inbound
  
  // short body
  and length(body.current_thread.text) < 500
  
  // NLU intent
  and (
    any(ml.nlu_classifier(body.current_thread.text).intents, .name != "benign")
    and length(ml.nlu_classifier(body.current_thread.text).intents) > 0
  )
  
  // free file host link
  and any(body.links,
          .href_url.domain.domain in $free_file_hosts
          or .href_url.domain.root_domain in $free_file_hosts
  )
  
  // freemail sender
  and sender.email.domain.root_domain in $free_email_providers
  and (
    not profile.by_sender().any_false_positives
    and not profile.by_sender().solicited
  )

tags:
  - "Attack surface reduction"
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Free email provider"
  - "Free file host"
  - "Social engineering"
detection_methods:
  - "Content analysis"
  - "Natural Language Understanding"
  - "Sender analysis"
  - "URL analysis"
id: "569817fe-96b5-5c1d-96dc-30cd1cb9fd16"