Credential Stuffing in Chi with Dynamodb

Credential stuffing is an automated attack technique where attackers use lists of previously compromised username and password pairs to gain unauthorized access to user accounts. In a Chi application backed by Dynamodb, this risk is amplified when authentication endpoints do not enforce adequate rate limiting or adaptive controls. Chi is a lightweight web framework for Clojure, and when its routes that interact with Dynamodb do not implement proper request throttling or anomaly detection, attackers can perform high-volume credential validation attempts without triggering defenses.

Dynamodb, as a NoSQL database, stores user credentials typically as items in a table with a primary key such as user_id or email. If an attacker discovers or guesses the attribute names used for authentication (for example, email as a partition key), they can efficiently probe the backend by sending authentication requests that query Dynamodb for existence checks. While Dynamodb itself does not inherently expose credential data, the application layer’s interaction with Dynamodb can leak information through timing differences or error messages that reveal whether a given credential exists in the table. This side-channel information enables attackers to iteratively refine credential lists and focus on valid accounts.

Chi routes that perform read operations from Dynamodb without enforcing per-IP or per-user rate limits create an environment conducive to credential stuffing. For example, an endpoint like /login that accepts a JSON payload with :email and :password and performs a GetItem on Dynamodb can be invoked repeatedly. Without controls such as request caps or CAPTCHA challenges after suspicious patterns, attackers can execute thousands of attempts per minute. middleBrick’s Authentication and Rate Limiting checks are designed to detect such weaknesses by analyzing unauthenticated attack surfaces and identifying missing rate controls around authentication flows.

Additionally, if the application does not uniformly handle errors—for instance, returning distinct messages for nonexistent users versus incorrect passwords—attackers can use this feedback to confirm valid email addresses. This technique, combined with the high throughput allowed by Dynamodb’s low-latency responses, makes credential stuffing feasible even for applications not directly exposed to the public internet if rate limiting and monitoring are absent. middleBrick’s detection of Authentication and Rate Limiting issues helps highlight these gaps before attackers exploit them.

To mitigate credential stuffing in Chi applications using Dynamodb, implement layered controls at the application and infrastructure level. Begin by introducing rate limiting directly in Chi routes that interact with Dynamodb. This can be achieved using middleware that tracks request counts per IP or per authenticated token within a sliding window. The following example demonstrates a simple rate-limiting middleware using an in-memory store, suitable for development or low-scale deployments.

(ns myapp.middleware
  (:require [ring.util.response :refer [response]]))

(def rate-store (atom {}))

(defn rate-limit [handler window-ms max-requests]
  (fn [request]
    (let [ip (:remote-addr request)
          now (System/currentTimeMillis)
          cutoff (- now window-ms)
          requests (get-in @rate-store [ip] ())]
      (;; Clean old entries
       (swap! rate-store assoc ip (filter #(> (:time %) cutoff) requests))
       (let [recent (count (get @rate-store ip))]
         (if (>= recent max-requests)
           {:status 429 :body (str "Rate limit exceeded" )}
           (do
             (swap! rate-store update-in [ip] conj {:time now})
             (handler request)))))))

;; Usage in a Chi route
(defn login-handler [request]
  (let [email (get-in request [:body-params :email])
        password (get-in request [:body-params :password])]
    ;; Perform Dynamodb GetItem or query here
    (response {:status :ok})))

(def app
  (-> login-handler
      (rate-limit 60000 10))) ;; 10 requests per 60 seconds per IP

On the Dynamodb side, ensure that authentication queries use parameterized inputs and avoid exposing detailed error information. Instead of returning different messages for missing users versus invalid passwords, use a consistent response such as Invalid credentials. Additionally, consider storing passwords using strong adaptive hashing algorithms like bcrypt or Argon2, and perform hashing outside of Dynamodb to reduce computational load on the database. The following example shows a simplified login flow that uses consistent error handling and interacts safely with Dynamodb using the AWS SDK for Clojure.

(ns myapp.auth
  (:require [aws.sdk.dynamodb :as ddb]
            [buddy.hashers :as hashers]))

(defn get-user-by-email [email]
  (ddb/get-item {:db dynamodb-client
                 :table-name "users"
                 :key {"email" {:s email}}}))

(defn verify-password [stored-hash candidate)
  (hashers/verify candidate stored-hash))

(defn login [email password]
  (let [user-record (get-user-by-email email)]
    (if (and user-record (verify-password (:password user-record) password))
      {:status :authenticated :user-id (:user_id user-record)}
      {:status :unauthorized :message "Invalid credentials"})))

For production-grade protection, combine these measures with continuous scanning using tools like middleBrick. Its CLI and GitHub Action integrations can be configured to fail builds or alert when authentication endpoints lack rate limiting or exhibit inconsistent error handling. The dashboard and MCP Server integrations further enable tracking security posture over time and embedding checks directly into development workflows, ensuring that credential stuffing risks are identified early and addressed consistently.