sublimehighRule

Attachment: Cold outreach with invitation subject and not attachment

Detects inbound messages with invitation-related subjects that request recipients to view attachments, contain no links, and are classified as B2B cold outreach with high confidence. Messages either have no attachments or contain a single image attachment.

MITRE ATT&CK

T1566 T1598

initial-access

Detection Query

type.inbound
and strings.icontains(subject.subject, 'invit')
and length(body.links) == 0
// please find attached language
and regex.icontains(body.current_thread.text,
                    '(?:please|find|view).{0,50}attached'
)
// a single image attachment or there are 0 attachments
and (
  (
    length(attachments) == 1
    and all(attachments, .file_type in $file_types_images)
  )
  or length(attachments) == 0
)
and any(ml.nlu_classifier(body.current_thread.text).topics,
        .name == "B2B Cold Outreach" and .confidence == "high"
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: Cold outreach with invitation subject and not attachment"
description: "Detects inbound messages with invitation-related subjects that request recipients to view attachments, contain no links, and are classified as B2B cold outreach with high confidence. Messages either have no attachments or contain a single image attachment."
type: "rule"
severity: "high"
source: |
  type.inbound
  and strings.icontains(subject.subject, 'invit')
  and length(body.links) == 0
  // please find attached language
  and regex.icontains(body.current_thread.text,
                      '(?:please|find|view).{0,50}attached'
  )
  // a single image attachment or there are 0 attachments
  and (
    (
      length(attachments) == 1
      and all(attachments, .file_type in $file_types_images)
    )
    or length(attachments) == 0
  )
  and any(ml.nlu_classifier(body.current_thread.text).topics,
          .name == "B2B Cold Outreach" and .confidence == "high"
  )
attack_types:
  - "Spam"
tactics_and_techniques:
  - "Social engineering"
  - "Image as content"
detection_methods:
  - "Content analysis"
  - "Natural Language Understanding"
  - "File analysis"
id: "883d04a9-a43d-5c9a-bb4b-b8b158e593fb"