Insecure Design in Chi with Dynamodb

Insecure design in a Chi application that uses DynamoDB often stems from modeling data and access patterns without enforcing authorization at the database layer. Because DynamoDB is a schemateless, key-value store, application-level checks must be explicit; omitting them creates an access control surface that invites IDOR and BOLA attacks.

Chi is a lightweight routing library for Clojure that encourages composable handlers. When a Chi route directly forwards a request to DynamoDB without validating ownership or tenant context, the route becomes an unauthenticated attack surface. For example, a route like /users/:user_id/profile that constructs a GetItem key from :user_id without verifying that the authenticated subject matches user_id enables horizontal privilege escalation.

DynamoDB-specific risks in this context include missing partition-key-level authorization, overly permissive IAM policies attached to the application role, and lack of server-side filtering. If the application uses a global secondary index (GSI) for queries and does not embed the user ID as part of the index key, an attacker can enumerate records across partitions. A real-world pattern is the CWE-287 Improper Authentication and OWASP API Broken Object Level Authorization, which maps to middleBrick’s BOLA/IDOR check.

Consider a DynamoDB table where the primary key is PK = USER# and a developer adds a GSI with GSI1PK = ROLE#admin but forgets to scope queries by user tenant. An attacker can issue a Query on the GSI to list all admin records globally. This is exacerbated when the application uses unauthenticated endpoints (e.g., health or public data endpoints) that share the same DynamoDB client, enabling SSRF-like data exposure through misconfigured VPC endpoints or IAM roles.

middleBrick’s LLM/AI Security checks are relevant here because insecure design can expose system prompts or error messages that reveal backend structure. For instance, verbose DynamoDB exceptions may leak table names or index structures, aiding further exploitation. The scanner tests for information leakage in responses and excessive agency patterns, which can indicate over-privileged roles or unsafe consumption of DynamoDB streams.

In Chi, the combination of dynamic routing, lack of middleware authorization, and permissive DynamoDB policies means findings often point to missing ownership checks and missing resource-level permissions. Remediation must address data modeling, client permissions, and runtime validation together.

Remediation centers on enforcing ownership at the point of data access, using the partition key to scope queries, and applying least-privilege IAM. Below are concrete patterns for Chi handlers that interact with DynamoDB.

1. Enforce ownership via partition key

Always include the authenticated subject in the key design. If your table uses PK and SK, derive PK from the user identifier and use it in every query.

;; Chi route with authenticated user bound to DynamoDB key
(defn profile-handler [{{user-id :path-params} :request}]
  (let [client (dynamodb/client)
        pk (str "USER#" user-id)
        req {:key {:pk {:s pk}
                   :sk {:s "PROFILE"}}
             :table-name "app-table"}]
    (try
      (dynamodb/get-item req)
      (catch Exception e
        {:status 500 :body "Unable to load profile"}))))

2. Use scoped queries with explicit filter on GSI

If you must use a GSI, include the user ID in the GSI key and filter on the server side to prevent cross-user enumeration.

(defn user-orders [{{user-id :path-params} :request}]
  (let [client (dynamodb/client)
        gsi-pk (str "USER#" user-id)
        req {:key-condition-expression "gsi-pk = :uid"
             :expression-attribute-values {":uid" {:s gsi-pk}}
             :table-name "orders-table"
             :index-name "GSI-USER-ORDERS"}]
    (dynamodb/query req)))

3. Apply least-privilege IAM via policy scoping

Ensure the application role can only access records scoped by prefix. In Terraform or CloudFormation, use condition keys like dynamodb:LeadingKeys so that a compromised credential cannot read or write outside the user’s partition.

# Example IAM policy condition (conceptual)
{
  "Effect": "Allow",
  "Action": [
    "dynamodb:GetItem",
    "dynamodb:Query"
  ],
  "Resource": "arn:aws:dynamodb:region:account:table/app-table/*",
  "Condition": {
    "ForAllValues:StringEquals": {
      "dynamodb:LeadingKeys": ["USER#"]
    }
  }
}

4. Validate and normalize IDs in Chi middleware

Add middleware that ensures the :user_id in the route matches the authenticated subject before hitting DynamoDB.

(defn auth-middleware [handler]
  (fn [request]
    (let [user-id (get-in request [:session :user-id])
          path-id (get-in request [:path-params "user_id"])]
      (if (= user-id path-id)
        (handler request)
        {:status 403 :body "Forbidden"}))))

5. Avoid exposing DynamoDB metadata in errors

Sanitize error messages returned to clients to prevent table or index name leakage, which middleBrick’s system prompt leakage detection can help identify.

(try
  (dynamodb/request req)
  (catch Exception e
    (log/error (str "DB error: " (.getMessage e)))
    {:status 500 :body "Internal error"}))

By combining these patterns, the Chi application reduces the attack surface for IDOR and BOLA, aligns with OWASP API Top 10 insecure design guidance, and satisfies many compliance mappings that middleBrick reports on.