GCP Free Gmail Domains Added To IAM Policy

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 * Copyright 2024 Google LLC
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 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
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 * distributed under the License is distributed on an "AS IS" BASIS,
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OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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 rule gcp_free_gmail_domains_added_to_iam_policy {

  meta:
    author = "Google Cloud Security"
    description = "Detect when free Google Email addressess are added to IAM Policy such as gmail.com, googlemail.com or googlegroups.com."
    rule_id = "mr_eec293b2-75d6-48f1-871d-182d67345a9c"
    rule_name = "GCP Free Gmail Domains Added To IAM Policy"
    mitre_attack_tactic = "Persistence"
    mitre_attack_technique = "Create Account: Cloud Account"
    mitre_attack_url = "https://attack.mitre.org/techniques/T1136/003/"
    mitre_attack_version = "v14.1"
    type = "Alert"
    data_source = "GCP Cloud Audit"
    platform = "GCP"
    severity = "High"
    priority = "High"

  events:
    $gcp.metadata.event_type = "USER_RESOURCE_UPDATE_PERMISSIONS"
    $gcp.metadata.log_type = "GCP_CLOUDAUDIT"
    $gcp.metadata.product_event_type = "SetIamPolicy"
    $gcp.metadata.product_name = "Google Cloud Platform"
    $gcp.metadata.vendor_name = "Google Cloud Platform"
    $gcp.security_result.action = "ALLOW"
    $gcp.target.resource.attribute.labels["ser_binding_deltas_action"] = "ADD"
    $gcp.target.resource.attribute.labels["ser_binding_deltas_member"] = /.*@gmail\.com
| .*@googlemail\.com
| .*@googlegroups\.com/ nocase

  outcome:
    $risk_score = max(75)
    $mitre_attack_tactic = "Persistence"
    $mitre_attack_technique = "Create Account: Cloud Account"
    $mitre_attack_technique_id = "T1136.003"
    $event_count = count_distinct($gcp.metadata.id)
    $network_http_user_agent = array_distinct($gcp.network.http.user_agent)
    $principal_ip = array_distinct($gcp.principal.ip)
    $principal_ip_country = array_distinct($gcp.principal.ip_geo_artifact.location.country_or_region)
    $principal_ip_state = array_distinct($gcp.principal.ip_geo_artifact.location.state)
    $principal_user_id = $gcp.principal.user.userid
    $principal_user_display_name = $gcp.principal.user.user_display_name
    $target_resource_name = $gcp.target.resource.name
    $event_name = $gcp.metadata.product_event_type
    $target_email_addresses = array_distinct($gcp.target.user.email_addresses)

  condition:
    $gcp
}