Insecure Design in Chi with Jwt Tokens

Insecure design in a Chi application that uses JWT tokens often arises when token validation is implemented without considering the full security lifecycle of the token. A common pattern is to decode the JWT and extract claims, such as the subject or roles, without verifying critical properties like the issuer (iss), audience (aud), and token expiration (exp). In Chi, this can occur when routing handlers rely on raw token payloads for authorization decisions without enforcing strict validation, effectively trusting any token that is well-formed.

For example, consider a Chi endpoint that extracts a role claim to permit access to an administrative route. If the handler decodes the JWT using a permissive library function that does not validate the signature or required claims, an attacker could supply a token signed with a weak algorithm (e.g., none) or with a modified payload that claims administrative privileges. This insecure design fails to treat the token as an untrusted input, enabling privilege escalation or unauthorized access.

Another aspect of insecure design is the storage and transmission of JWTs within the Chi application. If tokens are logged, exposed in URLs, or stored insecurely in client-side code, the confidentiality and integrity of the token can be compromised. Chi handlers that expose debug endpoints or reflection of request headers may inadvertently leak token material. Additionally, relying on weak signing keys or failing to rotate keys increases the risk of token forgery. The combination of weak validation, excessive trust in client-supplied claims, and poor operational practices creates a design that does not adequately protect the token lifecycle.

Middleware configuration in Chi also plays a role. If the JWT verification middleware is not applied consistently across protected routes or is conditionally bypassed based on development flags, the attack surface expands. An attacker may identify routes where token validation is skipped and target those endpoints directly. Furthermore, insufficient error handling in the verification process can lead to information disclosure or inconsistent enforcement, compounding the insecure design.

Real-world attack patterns such as CVE-2020-28168, which involves algorithm confusion in JWT libraries, illustrate the risks when token validation is not rigorous. In a Chi service that does not explicitly specify the expected algorithm and does not validate claims, such vulnerabilities can be exploited to forge tokens and impersonate users.

To summarize, insecure design in Chi with JWT tokens emerges when token handling lacks rigorous validation, fails to enforce claim checks, exposes tokens inadvertently, or applies security measures inconsistently. This creates an environment where forged or tampered tokens can be accepted as valid, undermining authentication and authorization controls.

Remediation focuses on strict JWT validation, secure middleware configuration, and safe handling of token data within Chi handlers. Always validate the signature, required claims, and token metadata. Use a well-maintained JWT library that supports algorithm enforcement and claim verification.

Below is a concrete example of secure JWT verification in a Chi application using the cheshire3 and bigneur libraries. The middleware decodes and validates the token before allowing access to protected routes.

(ns myapp.middleware
  (:require [bigneur.core :refer [jwt-decode]]))

(defn verify-jwt [secret-token]
  (fn [request handler]
    (let [auth-header (get-in request [:headers "authorization"])
          token (when auth-header (clojure.string/replace auth-header #"^Bearer " ""))]
      (if token
        (try
          (let [claims (jwt-decode token {:secret secret-token :alg :hs256})
                exp (:exp claims)
                now (System/currentTimeMillis)
                issuer (:iss claims)
                audience (:aud claims)]
            (if (and (not (nil? exp)) (>= exp (quot now 1000))
                     (= issuer "my-trusted-issuer")
                     (= audience "my-api-audience"))
              (handler request)
              {:status 401 :body "Invalid token claims"}))
          (catch Exception e
            {:status 401 :body "Token verification failed"}))
        {:status 401 :body "Missing token"}))))

(def secured-routes
  (-> (ring/ring-handler
       (ring/routes
         (GET "/public" [] {:status 200 :body "public"})
         (GET "/admin" request
           (if (some? (:user request))
             {:status 200 :body "admin data"}
             {:status 403 :body "forbidden"}))
         (route/not-found "Not found"))
       (wrap-defaults site-defaults)
       (verify-jwt "your-256-bit-secret"))
      (wrap-defaults api-defaults)))

In this example, the verify-jwt function checks the presence of the token, validates the signature using HS256, ensures the expiration time is in the future, and verifies the issuer and audience claims. The middleware returns a 401 status for missing or invalid tokens, preventing unauthorized access. This approach addresses insecure design by enforcing strict validation and avoiding trust in raw token contents.

Additionally, ensure that tokens are transmitted only over HTTPS, stored securely on the client side (e.g., in HttpOnly cookies with Secure and SameSite attributes), and never logged or exposed in URLs. Rotate signing keys periodically and define clear token lifetimes to reduce the impact of a compromised token.

For applications using asymmetric keys, validate the token with the correct public key and explicitly set the allowed algorithms to prevent algorithm confusion attacks. Avoid accepting tokens with alg: none and always specify the expected algorithm in the decoding call. These practices align with secure design principles and mitigate common JWT-related vulnerabilities.