sublimehighRule

Attachment: ICS calendar file with recipient address in UID field

Detects inbound messages containing ICS calendar attachments where the UID property matches the recipient's email address, indicating potential calendar-based social engineering.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598

initial-access

Detection Query

type.inbound
and any(attachments,
        (
          .file_type == "ics"
          or (
            .file_extension == "ics"
            or .content_type in ("application/ics", "text/calendar")
          )
        )
        //
        // 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 any(beta.file.parse_ics(.).events,
                any(.raw_properties,
                    .key == "UID" and .value == recipients.to[0].email.email
                )
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: ICS calendar file with recipient address in UID field"
description: "Detects inbound messages containing ICS calendar attachments where the UID property matches the recipient's email address, indicating potential calendar-based social engineering."
type: "rule"
severity: "high"
source: |
  type.inbound
  and any(attachments,
          (
            .file_type == "ics"
            or (
              .file_extension == "ics"
              or .content_type in ("application/ics", "text/calendar")
            )
          )
          //
          // 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 any(beta.file.parse_ics(.).events,
                  any(.raw_properties,
                      .key == "UID" and .value == recipients.to[0].email.email
                  )
          )
  )
  
attack_types:
  - "Credential Phishing"
tactics_and_techniques:
  - "Social engineering"
detection_methods:
  - "File analysis"
  - "Content analysis"
id: "507d814e-1db5-56ce-929f-13c4c78b345f"