Memory Leak in Chi with Jwt Tokens

A memory leak in a Chi application that uses JWT tokens typically occurs when token state or related resources are retained beyond their intended lifetime. In a functional-first language like Clojure, common sources include holding references to token payloads, parsed claims, or cryptographic material in long-lived atoms or caches without cleanup. Because Chi routes are often composed as functions that return responses, developers may inadvertently attach token metadata to request maps (e.g., via :request or :session) and store those maps in global refs or databases without expiration. JWT tokens themselves are stateless, but application-level handling can introduce state that accumulates over time.

For example, if each request decodes a JWT and stores the resulting claims map in an atom for later access across middleware or handlers, and that atom is never pruned, memory consumption grows with each unique token processed. This is particularly problematic when tokens carry large payloads or when the application scales to handle many concurrent users. In Chi, middleware that enriches the request map with decoded token data must ensure that enriched data is ephemeral to the request lifecycle and not retained globally. Another scenario involves caching libraries or in-memory stores used to hold validated token keys or revocation lists without size limits or TTLs, leading to unbounded growth. Because Chi encourages composable, data-driven handlers, it is easy to chain middleware that inadvertently retain references, turning what should be lightweight token validation into a persistent memory burden.

From a security perspective, unchecked memory growth can degrade service stability and amplify denial-of-service risks. While memory leaks do not directly expose token content, they can lead to resource exhaustion that interrupts legitimate authentication flows, potentially forcing restarts and causing availability impacts. In environments where JWT tokens are validated on every request, the combination of frequent token processing and improper resource management increases the likelihood of observable performance degradation. middleBrick’s scans can detect patterns consistent with resource abuse by analyzing runtime behavior and configuration; for instance, scans that include Inventory Management and Rate Limiting checks may surface anomalies tied to token handling inefficiencies. Organizations using the Pro plan benefit from continuous monitoring that can alert on abnormal resource trends, helping correlate memory metrics with authentication activity.

Remediation focuses on ensuring token-related data does not persist beyond a single request and that cryptographic operations are scoped appropriately. In Chi, prefer local bindings within handler functions and avoid attaching decoded claims to the request map in a way that is stored globally. Use middleware to decode the token, validate it, and pass only necessary, transient data forward via the request map without retaining references outside the request scope.

Example: Safe JWT validation in a Chi handler

(ns myapp.handler
  (:require [cheshire.core :as json]
            [buddy.sign.jwt :as jwt]
            [compojure.core :refer [GET defroutes]]))

(def secret-key "your-secure-key-here")

(defn validate-jwt [token]
  (try
    (jwt/verify token secret-key {:alg "HS256"})
    (catch Exception e
      (throw (ex-info "Invalid token" {:type ::invalid-token})))))

(defn auth-middleware [handler]
  (fn [request]
    (if-let [token (some-> request :headers (get "authorization"))]
      (let [token-payload (validate-jwt (subs token 7))] ;; remove "Bearer "
        ;; Use token-payload locally; do not attach to request if not needed
        (handler (assoc request :token-payload token-payload)))
      (handler request))))

(defroutes app-routes
  (GET "/profile"
    [token-payload] ;; receive as a local parameter
    {:status 200
     :body (json/generate-string {:user (:sub token-payload)}))}
  (route/not-found "Not found"))

(def app
  (-> app-routes auth-middleware)

In this pattern, token-payload is a transient map used only within the handler. No atoms, refs, or caches retain it after the response is sent. The secret key is loaded from a secure configuration source at runtime, and token verification is performed per request without storing intermediate state.

Avoiding cache-based retention

(ns myapp.cache
  (:require [taoensso.carmine :as car]))

;; Avoid unbounded storage of token-related keys
(defn safe-check [token]
  (let [valid? (jwt/verifiable? token)]
    ;; Do not store token or claims in a global cache without TTL
    valid?))

;; If caching is required, enforce limits and TTL
(defn cached-validate [token]
  (car/with-conn
    (car/setex "valid-tokens" 3600 token "verified")))

When caching is necessary, enforce time-to-live (TTL) and size limits to prevent unbounded growth. Prefer short-lived entries and avoid storing raw tokens or sensitive claims. For teams using the Pro plan, continuous monitoring can alert on anomalies in cache size or request rates that may indicate inefficient token handling.

Operational guidance

Instrument your Chi services to track memory usage per request and correlate spikes with authentication events. Use middleware timing and metrics to identify handlers that retain data. If integrating with CI/CD, the GitHub Action can enforce security thresholds that include resource usage patterns; failing builds when anomalies are detected helps catch regressions early. The MCP Server enables rapid scanning from development environments, allowing you to validate token-handling logic before deployment.