Cache Poisoning in Gorilla Mux with Jwt Tokens

Cache poisoning occurs when an attacker influences cached responses so that subsequent users receive malicious or incorrect data. When using Gorilla Mux with JWT tokens, the risk arises if request variations tied to authorization are improperly normalized or cached without considering the per-user nature of the token. Gorilla Mux is a powerful URL router and dispatcher for Go; in combination with JWT bearer tokens, a developer might configure route-level caching at the application or infrastructure layer (for example via a CDN or reverse proxy) that uses the request path as the cache key while failing to exclude or properly scope the Authorization header.

Consider a scenario where an API endpoint protected by JWT is also served from a cache keyed only on the path and query parameters. If an attacker can get a victim’s request—including the valid JWT—cached, the cached response containing the victim’s data or an altered representation could be replayed to other users who share the same path but have different authorization contexts. This is particularly relevant when tokens carry user roles or tenant identifiers that should prevent cross-user data exposure. Because JWTs often carry sensitive claims, leaking them via cache storage or reflected in error responses increases exposure. Insecure default caching behavior, such as caching authenticated responses without Vary headers that account for Authorization, compounds the issue by allowing intermediaries to serve one user’s authorized response to another.

Additionally, if route variables or query parameters derived from token claims are used to construct cache keys without validation, an attacker may manipulate those inputs to poison the cache with crafted URLs. For example, an endpoint like /api/tenant/{id} where id is extracted from a JWT and used in cache logic could be tricked into caching attacker-controlled content under a key that appears legitimate. The interplay between Gorilla Mux’s pattern matching and JWT-based authorization logic must be carefully designed so that cache keys incorporate user or tenant context or exclude sensitive paths from caching entirely.

To mitigate cache poisoning when using JWT tokens with Gorilla Mux, ensure that authorization-sensitive responses are either excluded from caching or cached with user- or tenant-specific keys. Below are concrete, idiomatic Go examples using Gorilla Mux and standard JWT handling that demonstrate secure patterns.

First, define a JWT validation middleware that extracts and verifies the token, then enriches the request context with user claims used for cache decisions:

import (
	"context"
	"net/http"
	"strings"

	"github.com/dgrijalva/jwt-go"
	"github.com/gorilla/mux"
)

type Claims struct {
	TenantID string `json:"tenant_id"`
	UserID   string `json:"user_id"`
	jwt.StandardClaims
}

func JWTMiddleware(secretKey []byte) mux.MiddlewareFunc {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			auth := r.Header.Get("Authorization")
			if auth == "" {
				http.Error(w, `{"error":"authorization header required`}", http.StatusUnauthorized)
				return
			}
			const bearerPrefix = "Bearer "
			if !strings.HasPrefix(auth, bearerPrefix) {
				http.Error(w, `{"error":"invalid authorization header`}", http.StatusUnauthorized)
				return
			}
			tokenString := auth[len(bearerPrefix):]
			claims := &Claims{}
			token, err := jwt.ParseWithClaims(tokenString, claims, func(token *jwt.Token) (interface{}, error) {
				return secretKey, nil
			})
			if err != nil || !token.Valid {
				http.Error(w, `{"error":"invalid token`}", http.StatusUnauthorized)
				return
			}
			ctx := context.WithValue(r.Context(), "claims", claims)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

Second, when caching at the application layer, incorporate tenant or user identifiers from the claims into the cache key to prevent cross-tenant or cross-user contamination:

import (
	"fmt"
	"net/http"
)

func cachedHandler(next http.Handler) http.Handler {
	cache := map[string][]byte{} // simplistic in-memory cache for illustration
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		claims, ok := r.Context().Value("claims").(*Claims)
		if !ok {
			http.Error(w, `{"error":"claims missing`}", http.StatusInternalServerError)
			return
		}
		// Build a cache key that includes tenant and path; vary by Authorization to avoid poisoning
		cacheKey := fmt.Sprintf("tenant:%s:path:%s", claims.TenantID, r.URL.Path)
		if resp, found := cache[cacheKey]; found {
			w.Write(resp)
			return
		}
		// Capture response, store in cache, then write
		// (implementation of response capture omitted for brevity)
		next.ServeHTTP(w, r)
	})
}

Third, at the infrastructure or proxy level, configure caching to respect the Vary header and to exclude paths that carry sensitive authorization data from shared caches. For CDN or reverse proxy rules, ensure that the Authorization header or a hash of the token’s tenant claim is part of the cache key or that authenticated routes are marked as private:

# Example pseudo-configuration for a caching layer (not executable Go)
# Vary: Authorization
# Cache-Control: private, no-store for authenticated routes that should not be cached

Finally, prefer using private (per-user) caches or no-store for endpoints where token claims affect authorization or data visibility. By combining JWT-aware middleware with tenant-aware cache keys and explicit cache-control directives, you reduce the chance that a poisoned entry for one user affects others in a Gorilla Mux–based service.