Broken Access Control in Phoenix with Cockroachdb

Broken Access Control occurs when authorization checks are missing or bypassed, allowing a user to access resources or perform actions they should not. In a Phoenix application using Cockroachdb as the backend, this risk is amplified by the interaction between application-level permissions, SQL query construction, and Cockroachdb’s identity and privilege model.

Phoenix typically relies on application-level guards (e.g., Guardian or Pow for authentication, and custom role checks) to enforce what a given user can do. However, if these guards are inconsistently applied around Cockroachdb queries—especially dynamic SQL or raw Ecto queries—a direct path exists for horizontal or vertical privilege escalation. For example, an endpoint that builds a WHERE clause using user-supplied IDs without verifying ownership can allow an authenticated user to view or modify another user’s records simply by changing an ID parameter.

With Cockroachdb, the database enforces its own access controls via roles and GRANTs. If the Phoenix application connects to Cockroachdb with a highly privileged account (e.g., root or a role with broad SELECT/UPDATE on user tables), and the application does not enforce row-level security itself, a compromised application account or a logic flaw can lead to wide data exposure. Additionally, Cockroachdb’s multi-region capabilities and secondary indexes can inadvertently expose data through poorly constructed queries that bypass intended partition keys, enabling data from other regions or tenants to be returned when authorization checks are skipped.

Consider an Ecto schema like UserPosts where a developer assumes visibility is limited by the caller’s session but constructs queries such as from(p in UserPost, where: p.id == ^id) without first confirming that the current user owns p.user_id. If an attacker iterates over numeric IDs, they can traverse records they should not see. Because Cockroachdb returns results quickly and supports complex joins across tables, an attacker may combine ID manipulation with crafted requests to infer schema details or extract sensitive data across tenant boundaries.

The OWASP API Top 10 category A1: Broken Access Control aligns with this pattern, and findings often map to SOC2 and GDPR controls around data segregation. In a continuous monitoring setup—such as that provided by the Pro plan with its GitHub Action integration—such misconfigurations can be caught before they reach production, preventing unauthorized data access across Cockroachdb-backed services.

To mitigate Broken Access Control in Phoenix with Cockroachdb, enforce strict ownership checks, use parameterized queries, and avoid overly permissive database roles. Below are concrete, safe patterns.

1. Always scope queries to the authenticated user

Ensure every data access includes the user’s ID. For example, using Ecto with a current_user_id derived from the session:

def list_user_posts(current_user_id) do
  from(p in UserPost,
    where: p.user_id == ^current_user_id,
    order_by: [desc: p.inserted_at]
  )
  |> Repo.all()
end

This guarantees that even if an attacker manipulates request parameters, they cannot access posts belonging to another user_id.

2. Use parameterized inputs, never string interpolation

Avoid interpolating IDs or other values directly into queries. Instead, rely on Ecto’s query syntax or explicit parameters:

# Safe: using ^ binding
Repo.get_by(UserPost, id: user_supplied_id, user_id: current_user_id)

# Unsafe pattern to avoid:
Repo.query("SELECT * FROM user_posts WHERE id = #{user_supplied_id}")

Cockroachdb treats literal injection points as potential vectors; binding parameters ensures proper escaping and plan stability.

3. Apply database roles with least privilege

Configure your Cockroachdb role for Phoenix to have only the permissions needed:

-- Example Cockroachdb role setup
CREATE ROLE phoenix_app WITH LOGIN PASSWORD 'strong_password';
GRANT SELECT, INSERT, UPDATE ON TABLE user_posts TO phoenix_app;
REVOKE DELETE ON TABLE user_posts FROM phoenix_app;

This limits what an application-level compromise can achieve. Avoid granting DBA or root roles to the application connection.

4. Enforce row-level ownership in business logic

For multi-tenant setups, combine Ecto changeset validation with explicit ownership checks before updates:

def update_post(%User{id: current_user_id}, post_id, attrs) do
  case Repo.get_by(UserPost, id: post_id, user_id: current_user_id) do
    nil -> {:error, :not_found_or_unauthorized}
    post ->
      post
      |> UserPost.changeset(attrs)
      |> Repo.update()
  end
end

This pattern ensures that updates are only permitted when both the ID matches and the user_id matches, closing a common authorization gap.

5. Validate and sanitize inputs before query construction

Even with correct scoping, malformed IDs can cause errors or information leaks. Validate IDs as positive integers and reject unexpected formats early in the pipeline:

def safe_id?(input) when is_binary(input) do
  case Integer.parse(input) do
    {int, ""} when int > 0 -> true
    _ -> false
  end
end

Integrate this validation into your pipeline or controller before constructing any Cockroachdb query.