sublimemediumRule

Attachment: PDF with secure document acknowledgment prompt

Detects PDF attachments matching yara rules looking for fake secure document prompts, including acknowledgment-style lures and suspicious image sizing.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598 T1036 T1027 T1598.003

defense-evasioninitial-access

Detection Query

type.inbound
and any(filter(attachments, .file_type == "pdf"),
        any(file.explode(.),
            any(.scan.yara.matches,
                .name in (
                  "pdf_prompt_ack_secure_document_link",
                  "pdf_prompt_ack_secure_document_image_sizes"
                )
            )
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: PDF with secure document acknowledgment prompt"
description: "Detects PDF attachments matching yara rules looking for fake secure document prompts, including acknowledgment-style lures and suspicious image sizing."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(filter(attachments, .file_type == "pdf"),
          any(file.explode(.),
              any(.scan.yara.matches,
                  .name in (
                    "pdf_prompt_ack_secure_document_link",
                    "pdf_prompt_ack_secure_document_image_sizes"
                  )
              )
          )
  )
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Evasion"
  - "PDF"
  - "Social engineering"
  - "Image as content"
  - "Impersonation: Brand"
detection_methods:
  - "Content analysis"
  - "File analysis"
  - "YARA"
id: "00d3962e-370b-54e1-bbfd-41a1e5eb36d5"