Broken Authentication in Phoenix with Cockroachdb

Broken Authentication in a Phoenix application using CockroachDB typically arises from a mismatch between session or token handling in the application layer and the database’s consistency and isolation guarantees. CockroachDB provides strong consistency and serializable isolation by default, which is excellent for correctness but can inadvertently expose authentication flaws if the application does not properly manage transactions, session state, and error handling.

One common pattern is authenticating a user via a SQL transaction that reads a user record, checks credentials, and then updates a last_login or session token field. If the transaction isolation level is not explicitly controlled or if retries are not handled correctly, the Phoenix application might proceed with an authenticated session even when the write did not fully commit due to serialization failures. This can lead to a situation where the application believes authentication succeeded (e.g., sets a session cookie) while the database state does not reflect the login, enabling horizontal or vertical privilege escalation (BOLA/IDOR) across requests.

CockroachDB’s serializable isolation means that concurrent authentication transactions can abort with retry errors. If Phoenix does not implement proper retry logic, an attacker can force transaction aborts to probe for timing differences or observe inconsistent authentication behavior. Additionally, if session identifiers or one-time tokens are stored in tables without proper unique constraints or checksums, an attacker might exploit weak token generation and predict or reuse identifiers across user accounts, a BFLA/Privilege Escalation vector.

Input validation gaps also contribute. For example, accepting user-supplied identifiers (such as user_id or email) and directly interpolating them into SQL without using parameterized queries or Ecto bindings can enable authentication bypass via SQL injection. Even when using Ecto, failing to scope queries by tenant or by proper ownership checks can allow an authenticated user to operate on other users’ data (IDOR) because the query does not enforce row-level security at the database interaction layer.

Because middleBrick scans the unauthenticated attack surface and tests endpoints like authentication flows and token handling, it can surface these authentication inconsistencies without requiring credentials. Its checks include Authentication, BOLA/IDOR, BFLA/Privilege Escalation, and Input Validation, which map to OWASP API Top 10 and can highlight risky patterns specific to Phoenix and CockroachDB integrations.

Remediation focuses on deterministic transactions, safe token handling, and strict query scoping. Use Ecto’s explicit transaction blocks with retry handling, enforce uniqueness and foreign-key constraints, and avoid any direct string interpolation in SQL strings.

1. Safe authentication transaction with retries

Wrap credential verification and session updates in a transaction with retry logic. CockroachDB may abort serializable transactions; handle {:error, %Ecto.StaleEntryError{}} or {:error, %Ecto.Query.StaleResultError{}} by retrying a bounded number of times.

defmodule MyApp.Accounts do
  import Ecto.Query, only: [from: 2]

  def authenticate_user(email, password) do
    MyApp.Repo.transaction(
      fn ->
        with {:ok, user} <- get_user_by_email(email),
             true <- Pbkdf2.verify_pass(password, user.password_hash),
             {:ok, _} <- MyApp.Repo.update(
               from(u in MyApp.User,
                 where: u.id == ^user.id,
                 update: [set: [last_login: ^DateTime.utc_now()]]
               )
             ) do
          {:ok, user}
        else
          false -> {:error, :unauthorized}
          error -> error
        end
      end,
      max_retries: 3
    )
  end

  defp get_user_by_email(email) do
    case MyApp.Repo.get_by(MyApp.User, email: email) do
      nil -> {:error, :not_found}
      user -> {:ok, user}
    end
  end
end

2. Enforce uniqueness and constraints at the database and schema level

Define unique indexes and foreign keys in migrations and in Ecto schemas to prevent token collisions and ensure referential integrity that supports robust ownership checks.

defmodule MyApp.Repo.Migrations.Add_unique_indexes do
  use Ecto.Migration

  def change do
    create unique_index(:users, [:email])
    create index(:user_sessions, [:user_id])
    create index(:user_sessions, [:token], unique: true)
    execute "ALTER TABLE user_sessions ADD CONSTRAINT fk_user FOREIGN KEY (user_id) REFERENCES users(id)"
  end
end

3. Parameterized queries and scoping to prevent IDOR

Always scope queries by tenant or ownership. Use Ecto bindings and explicit where clauses instead of interpolating identifiers.

def get_user_resource(user_id, resource_id) do
  from(r in MyApp.Resource,
    where: r.user_id == ^user_id and r.id == ^resource_id,
    select: r
  )
  |> MyApp.Repo.one()
end

4. Secure token generation and storage

Generate cryptographically random tokens and store only hashes. Avoid returning raw tokens after creation, and set appropriate constraints on length and uniqueness in the schema.

token = :crypto.strong_rand_bytes(32) |> Base.url_encode64(padding: false)
hashed_token = Pbkdf2.hash_pwd_salt(token)

MyApp.Repo.insert!(%MyApp.UserSession{user_id: user.id, token_hash: hashed_token})
# Only return the raw token to the client once; never store it.

By combining these patterns with middleBrick’s continuous monitoring and CI/CD integration (GitHub Action), teams can detect authentication regressions early and keep the Phoenix–CockroachDB stack aligned with secure defaults.