High Severity

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.

References

No references.

Sublime Security
Created Apr 20th, 2026 • Last updated Apr 20th, 2026
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
                )
        )
)
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