Pub/Sub Topics are anonymously or publicly accessible

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Metadata

Id: 7sdj7dsj8-f348-4f95-845c-1090e41a615c

Cloud Provider: GCP

Platform: Terraform

Severity: Medium

Category: Insecure Configurations

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Description

Google Cloud Pub/Sub Topics should not be configured to allow public access by assigning IAM roles to the special principals allUsers or allAuthenticatedUsers. Granting roles to these principals makes the topic accessible to anyone on the internet or to any authenticated Google user, exposing your data to unauthorized access or misuse. For example:

resource "google_pubsub_topic_iam_member" "bad_example" {
  topic  = "example-topic"
  member = "allUsers"
  role   = "roles/pubsub.publisher"
}

To prevent this, restrict the member attribute to specific users or service accounts, as shown below:

resource "google_pubsub_topic_iam_member" "good_example" {
  topic  = "example-topic"
  member = "user:someone@example.com"
  role   = "roles/pubsub.publisher"
}

Compliant Code Examples

# IAM Binding compliant
resource "google_pubsub_topic_iam_binding" "good_example_binding" {
  topic   = "example-topic"
  members = ["user:someone@example.com", "group:admins@example.com"] # ✅ No public principals
  role    = "roles/pubsub.subscriber"
}

# IAM Member compliant
resource "google_pubsub_topic_iam_member" "good_example_member" {
  topic  = "example-topic"
  member = "user:someone@example.com" # ✅ Non-public principal
  role   = "roles/pubsub.publisher"
}

Non-Compliant Code Examples

# IAM Member violation
resource "google_pubsub_topic_iam_member" "bad_example_member" {
  topic  = "example-topic"
  member = "allUsers" # ❌ Public principal
  role   = "roles/pubsub.publisher"
}

# IAM Binding violation
resource "google_pubsub_topic_iam_binding" "bad_example_binding" {
  topic   = "example-topic"
  members = ["allAuthenticatedUsers", "user:someone@example.com"] # ❌ Contains public principal
  role    = "roles/pubsub.subscriber"
}