Token Leakage in Chi

Token leakage in Chi APIs occurs when authentication tokens or session identifiers are inadvertently exposed through error responses, logging mechanisms, or improper response handling. This vulnerability is particularly concerning in Chi applications because the framework's middleware chain and error handling patterns can inadvertently expose sensitive authentication data.

The most common manifestation appears in error handling middleware. When a request fails due to authentication issues, Chi's default error handlers may include the original request context in error responses, potentially exposing Authorization headers or JWT tokens. Consider this problematic pattern:

router := chi.NewRouter()
router.Use(middleware.Logger)
router.Use(middleware.Recoverer)
router.NotFound(func(w http.ResponseWriter, r *http.Request) {
    // This may log the full request including Authorization header
    log.Println(r.Header.Get("Authorization"))
    http.Error(w, "Not Found", 404)
})

Another Chi-specific vector involves the RequestID middleware. While useful for debugging, if RequestID values correlate with user sessions or contain predictable patterns, they can become an attack surface. Attackers who discover one valid RequestID might enumerate others to map user activity or identify valid tokens.

Middleware chaining in Chi creates additional exposure points. Each middleware in the chain receives the full request context, and poorly implemented middleware might log sensitive headers or store them in contexts that persist beyond their intended scope. The framework's emphasis on composable middleware, while powerful, requires careful attention to what data flows through the chain.

Query parameter handling presents another Chi-specific concern. The framework's router automatically parses URL parameters, and if these parameters are used for authentication or contain tokens, they might appear in server logs, browser history, or be inadvertently exposed through error messages when routing fails.

Detecting token leakage in Chi applications requires examining both the middleware chain and error handling patterns. The first step is reviewing all middleware implementations to identify where request headers, particularly Authorization and Cookie headers, are accessed or logged.

middleBrick's black-box scanning approach is particularly effective for Chi applications because it tests the unauthenticated attack surface without requiring source code access. The scanner examines how the API responds to malformed requests, authentication failures, and error conditions—exactly when token leakage is most likely to occur.

For Chi applications, middleBrick specifically checks:

• Error responses that include request context or headers
• Middleware that logs full request objects
• Rate limiting implementations that might expose token information
• 404 and 405 handlers that return detailed error information
• OpenAPI spec analysis to identify authentication endpoints that might leak tokens in documentation

Manual detection involves testing Chi's error handling by sending requests that trigger various error conditions. For example, accessing non-existent routes, sending malformed JSON to endpoints expecting specific structures, or triggering middleware validation failures. Monitor the responses for any inclusion of request headers, tokens, or authentication metadata.

Chi's structured logging middleware can be a double-edged sword. While it provides excellent request tracing, if configured to log full requests, it may capture Authorization headers. Review logging configurations to ensure sensitive headers are redacted before logging.

Another detection technique involves examining middleware composition. Chi's middleware stack executes in order, so a logging middleware placed before authentication middleware might log unauthenticated requests containing tokens from previous requests or client-side storage.

Remediating token leakage in Chi applications requires a layered approach focused on proper middleware design and secure error handling. The foundation is implementing a security-focused middleware that redacts sensitive headers before they reach logging or error handling components.

func secureHeadersMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Create a copy of the request without sensitive headers
        secureReq := r.Clone(r.Context())
        secureReq.Header.Del("Authorization")
        secureReq.Header.Del("Cookie")
        
        next.ServeHTTP(w, secureReq)
    })
}

router := chi.NewRouter()
router.Use(secureHeadersMiddleware)
router.Use(middleware.Logger)
router.Use(middleware.Recoverer)

For error handling, implement custom error handlers that never include request context in responses:

func errorHandler(err error, w http.ResponseWriter, r *http.Request) {
    // Log the error internally with minimal context
    log.Printf("Error processing request: %v", err)
    
    // Generic error response without any sensitive information
    http.Error(w, "An error occurred. Please try again.", 500)
}

router := chi.NewRouter()
router.Use(middleware.Recoverer)
router.NotFound(func(w http.ResponseWriter, r *http.Request) {
    http.Error(w, "Resource not found", 404)
})

Chi's context package provides excellent mechanisms for secure data handling. Use context values instead of headers for passing authentication information between middleware:

func authMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        token := r.Header.Get("Authorization")
        if token == "" {
            http.Error(w, "Unauthorized", 401)
            return
        }
        
        // Store only necessary claims in context, not the raw token
        ctx := context.WithValue(r.Context(), "user_id", claims.UserID)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

Implement request sanitization middleware that removes or masks sensitive data before it reaches any logging or monitoring components:

func sanitizeRequestMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Create sanitized request for logging
        sanitized := r.Clone(r.Context())
        sanitized.Header.Del("Authorization")
        sanitized.Header.Del("Cookie")
        
        // Log sanitized request
        logRequest(sanitized)
        
        next.ServeHTTP(w, r)
    })
}

For comprehensive protection, combine these approaches with middleBrick's continuous scanning to ensure no new token leakage vectors emerge as the application evolves. The scanner's LLM security checks are particularly relevant for Chi applications that serve AI/ML endpoints, as these often have unique token handling requirements.