sublimemediumRule

Impersonation: Recipient organization in sender display name with credential theft image

Sender display name contains the recipient's organization domain while the actual email address differs. Message includes a single image attachment with OCR-detected credential theft language referencing the recipient's domain, and has no body text.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1598.003

initial-access

Detection Query

type.inbound
and length(body.links) <= 1
and length(attachments) == 1
and strings.icontains(sender.display_name, recipients.to[0].email.domain.sld)
and length(recipients.to) == 1
and recipients.to[0].email.domain.root_domain in $org_domains
and 
// No body text
(
  length(body.current_thread.text) == 0 or body.current_thread.text is null
)
and all(attachments,
        .file_type in $file_types_images
        //
        // This rule makes use of a beta feature and is subject to change without notice
        // using the beta feature in custom rules is not suggested until it has been formally released
        //
        and strings.icontains(beta.ocr(.).text,
                              recipients.to[0].email.domain.sld
        )
        and any(ml.nlu_classifier(beta.ocr(.).text).intents,
                .name == "cred_theft" and .confidence == "high"
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Impersonation: Recipient organization in sender display name with credential theft image"
description: "Sender display name contains the recipient's organization domain while the actual email address differs. Message includes a single image attachment with OCR-detected credential theft language referencing the recipient's domain, and has no body text."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and length(body.links) <= 1
  and length(attachments) == 1
  and strings.icontains(sender.display_name, recipients.to[0].email.domain.sld)
  and length(recipients.to) == 1
  and recipients.to[0].email.domain.root_domain in $org_domains
  and 
  // No body text
  (
    length(body.current_thread.text) == 0 or body.current_thread.text is null
  )
  and all(attachments,
          .file_type in $file_types_images
          //
          // This rule makes use of a beta feature and is subject to change without notice
          // using the beta feature in custom rules is not suggested until it has been formally released
          //
          and strings.icontains(beta.ocr(.).text,
                                recipients.to[0].email.domain.sld
          )
          and any(ml.nlu_classifier(beta.ocr(.).text).intents,
                  .name == "cred_theft" and .confidence == "high"
          )
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Image as content"
  - "Impersonation: Brand"
  - "Social engineering"
detection_methods:
  - "Computer Vision"
  - "Content analysis"
  - "File analysis"
  - "Natural Language Understanding"
  - "Optical Character Recognition"
  - "Sender analysis"
id: "6abfb20e-ca83-5e24-ad1e-609e6df9dd24"