Broken Access Control in Koa with Cockroachdb

Broken Access Control occurs when application logic fails to enforce proper authorization checks, allowing one user to access or modify another user’s resources. In a Koa application backed by Cockroachdb, this risk is amplified when route handlers construct SQL queries using unvalidated user input such as route parameters or decoded JWT subject claims. Cockroachdb, while PostgreSQL-wire compatible, enforces strict isolation for distributed transactions, but it does not automatically prevent an attacker from changing the subject of a query if the application supplies an insecure identifier.

Consider a typical pattern where an endpoint like /api/users/:userId/profile uses a decoded JWT payload to decide what to query. If the handler trusts ctx.params.userId without verifying that it matches the authenticated principal, an attacker can modify the path segment to view or update any profile. Because Cockroachdb supports schema constructs like partial indexes and check constraints, developers may assume these features enforce authorization, but constraints are not a substitute for explicit checks at the application layer.

Another common vector is multi-tenant queries built with string concatenation or naive template literals. For example, constructing a WHERE clause as WHERE tenant_id = ${tenantFromToken} without validating that the token’s tenant aligns with the request context can lead to tenant-to-tenant data leakage. Cockroachdb’s serializable isolation prevents some race conditions, yet it does not stop a malicious actor from supplying a different tenant identifier if the application fails to bind the correct value from a trusted source.

Middleware that only checks authentication (e.g., JWT presence) but omits authorization logic is insufficient. Without verifying roles, scopes, or resource ownership, endpoints expose sensitive information or allow privilege escalation. In distributed Cockroachdb deployments, improperly configured secondary indexes or overlooked default values in schema definitions can further obscure whether the query predicate aligns with the intended access boundary.

To illustrate, a vulnerable Koa handler might look like this:

// Vulnerable: no ownership or role check
router.get('/api/users/:userId', async (ctx) => {
  const { userId } = ctx.params;
  const { rows } = await pool.query('SELECT email, name FROM profiles WHERE id = $1', [userId]);
  ctx.body = rows[0];
});

An attacker who knows another user’s ID can directly retrieve that profile. Even if the table has a unique constraint on email, the absence of an access control check means the constraint does not protect against unauthorized reads.

Remediation focuses on ensuring every query incorporates the authenticated subject and, where applicable, the tenant context, using strongly typed parameters rather than string interpolation. Always bind user input as query parameters to avoid SQL injection and ensure the execution plan remains stable in Cockroachdb.

First, enforce ownership by joining the profiles table with the authenticated user identifier obtained from a verified JWT. Assume the authentication middleware sets ctx.state.user with verified claims:

// Secure: enforce ownership via authenticated subject
router.get('/api/users/me', async (ctx) => {
  const user = ctx.state.user; // { id, tenantId, roles }
  const { rows } = await pool.query(
    'SELECT email, name FROM profiles WHERE id = $1 AND tenant_id = $2',
    [user.id, user.tenantId]
  );
  ctx.body = rows[0] || ctx.throw(404, 'Profile not found');
});

This pattern ensures that even if an attacker manipulates the route, the server does not expose data across users because the query binds the authenticated ID directly.

For tenant-aware endpoints, validate the relationship before querying. Use a parameterized query that references both tenant and resource identifiers:

// Secure: tenant-aware and ownership-checked query
router.get('/api/records/:recordId', async (ctx) => {
  const user = ctx.state.user;
  const { recordId } = ctx.params;
  const { rows } = await pool.query(
    'SELECT data FROM records WHERE id = $1 AND tenant_id = $2',
    [recordId, user.tenantId]
  );
  ctx.body = rows[0] || ctx.throw(403, 'Access denied');
});

Roles and scopes can be enforced by inspecting user.roles before allowing sensitive operations:

// Secure: role-based authorization
router.delete('/api/records/:recordId', async (ctx) => {
  const user = ctx.state.user;
  const { recordId } = ctx.params;
  if (!user.roles.includes('admin')) {
    ctx.throw(403, 'Insufficient permissions');
  }
  const { rowCount } = await pool.query(
    'DELETE FROM records WHERE id = $1 AND tenant_id = $2',
    [recordId, user.tenantId]
  );
  if (rowCount === 0) ctx.throw(404, 'Record not found or access denied');
  ctx.status = 204;
});

Schema design in Cockroachdb can support these checks via partial indexes that align with tenant and ownership predicates, but the application must still supply the correct bound values. For example, an index like CREATE INDEX idx_profiles_tenant_id ON profiles(tenant_id) WHERE tenant_id IS NOT NULL improves performance but does not replace runtime authorization logic.

Finally, prefer centralized authorization logic to avoid duplication. A small helper can encapsulate tenant and ownership checks:

// Secure: reusable authorization helper
async function ensureProfileAccess(pool, userId, tenantId) {
  const { rows } = await pool.query(
    'SELECT 1 FROM profiles WHERE id = $1 AND tenant_id = $2',
    [userId, tenantId]
  );
  return rows.length > 0;
}

router.get('/api/profiles/:profileId', async (ctx) => {
  const user = ctx.state.user;
  const ok = await ensureProfileAccess(pool, user.id, user.tenantId);
  if (!ok) ctx.throw(403, 'Forbidden');
  ctx.body = { profileId: ctx.params.profileId };
});

By combining verified subject binding, tenant-aware predicates, and explicit role checks, the Koa + Cockroachdb stack can mitigate Broken Access Control while preserving the database’s distributed consistency guarantees.