sublimemediumRule

Attachment: Google share.google URL shortener in google.<tld>/share.google path form

Detects inbound messages whose attachments contain links in the form google.<tld>/share.google?q=<code>, which inherits google.<tld> domain reputation to mask an attacker-controlled destination. This google.<tld>/share.google?q= path form is undocumented: Google publishes the share.google shortener feature, but not this on-Google-domain form or its 'q' parameter. ICS calendar attachments are covered by a separate rule.

MITRE ATT&CK

T1566 T1566.001 T1566.002 T1598

initial-access

Detection Query

type.inbound
and any(attachments,
        not (
          .file_type == "ics"
          or .file_extension == "ics"
          or .content_type in ("application/ics", "text/calendar")
        )
        and any(file.explode(.),
                any(.scan.url.urls,
                    .domain.sld == "google"
                    and strings.istarts_with(.path, '/share.google')
                    and 'q' in keys(.query_params_decoded)
                )
        )
)

Data Sources

Email MessagesEmail HeadersEmail Attachments

Platforms

Raw Content

name: "Attachment: Google share.google URL shortener in google.<tld>/share.google path form"
description: "Detects inbound messages whose attachments contain links in the form google.<tld>/share.google?q=<code>, which inherits google.<tld> domain reputation to mask an attacker-controlled destination. This google.<tld>/share.google?q= path form is undocumented: Google publishes the share.google shortener feature, but not this on-Google-domain form or its 'q' parameter. ICS calendar attachments are covered by a separate rule."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and any(attachments,
          not (
            .file_type == "ics"
            or .file_extension == "ics"
            or .content_type in ("application/ics", "text/calendar")
          )
          and any(file.explode(.),
                  any(.scan.url.urls,
                      .domain.sld == "google"
                      and strings.istarts_with(.path, '/share.google')
                      and 'q' in keys(.query_params_decoded)
                  )
          )
  )
attack_types:
  - "Spam"
  - "Credential Phishing"
tactics_and_techniques:
  - "Open redirect"
  - "Social engineering"
detection_methods:
  - "URL analysis"
  - "Content analysis"
  - "File analysis"
related_detections:
  - "link_google_share_google.yml"
  - "attachment_ics_google_share_google_link.yml"
id: "840d7a90-3b3a-5fe1-a9c6-eac5deb4c14f"