Api Key Exposure in Chi

Api Key Exposure in Chi manifests through several distinct attack patterns that stem from the framework's unique architecture and deployment model. Chi's middleware-based routing system, while elegant, creates specific exposure points that attackers frequently exploit.

The most common pattern occurs in middleware chains where authentication tokens are passed between handlers. Chi's context package allows handlers to share data, but improper handling can lead to API keys being logged or exposed in error responses. For example, when a middleware captures an API key from headers but fails to sanitize it before passing to the next handler, the key might appear in stack traces or debug logs.

Another Chi-specific manifestation involves route parameter handling. Chi's path parameter extraction can inadvertently capture API keys embedded in URLs. Consider this vulnerable pattern:

router.Get("/api/v1/users/{userID}/data", func(w http.ResponseWriter, r *http.Request) {
    // API key might be in URL path or headers
    apiKey := r.Header.Get("Authorization")
    userID := chi.URLParam(r, "userID")
    
    // Vulnerable: logging without sanitization
    log.Printf("Processing request for user %s with API key %s", userID, apiKey)
})

This code logs the API key in plaintext, creating a persistent exposure vector. Attackers who gain access to log files can extract valid credentials.

Chi's middleware composition model also creates exposure risks through improper error handling. When authentication middleware fails and propagates errors up the chain, sensitive data including API keys might be included in error responses. The framework's default error handling doesn't automatically sanitize sensitive headers or parameters.

Environment variable handling in Chi applications presents another exposure vector. Many Chi applications use environment variables for configuration, but if these variables contain API keys and are logged or exposed through admin endpoints, they become vulnerable. This is particularly problematic in containerized deployments where environment dumps might be accessible.

Cross-origin resource sharing (CORS) misconfigurations in Chi applications can also lead to API key exposure. If CORS headers are too permissive, API keys in request headers might be accessible to malicious front-end applications through browser debugging tools.

Rate limiting middleware in Chi, when improperly implemented, can expose API key usage patterns. Attackers can monitor response times or error codes to infer valid API keys, especially when the middleware reveals whether a key exists or is rate-limited.

Session fixation attacks in Chi applications often target API key management. If an application doesn't properly rotate or invalidate API keys after authentication, attackers can capture and reuse keys from legitimate sessions.

Detecting API key exposure in Chi applications requires a multi-layered approach that leverages both static analysis and runtime scanning. middleBrick's specialized Chi scanning module identifies exposure patterns unique to the framework.

Static analysis begins with examining middleware chains for improper data handling. middleBrick analyzes Chi's middleware.Chain composition to identify where API keys might be passed between handlers without proper sanitization. The scanner specifically looks for patterns like:

// Vulnerable pattern detected by middleBrick
middleware := middleware.Chain(
    authMiddleware,
    loggingMiddleware,
    errorHandler,
)

The scanner traces data flow through this chain to identify where sensitive information might be exposed.

middleBrick's runtime scanning tests Chi's routing table to identify endpoints that might expose API keys through URL parameters or headers. The scanner attempts requests with various API key formats to see if they're reflected in responses or logs. It specifically tests Chi's path parameter extraction:

// middleBrick tests for this pattern
router.Get("/api/v1/{resource}/{id}", handler)

The scanner attempts to inject API keys into path parameters to see if they're logged or exposed.

middleBrick analyzes Chi's error handling middleware to identify where exceptions might expose API keys. It sends malformed requests designed to trigger error conditions and examines the responses for sensitive data leakage. The scanner specifically looks for patterns where error responses include request headers or parameters.

Environment variable scanning is another critical component. middleBrick examines the application's configuration loading to identify where API keys might be stored in environment variables and whether they're properly protected. The scanner tests for common patterns like:

// Detected by middleBrick
apiKey := os.Getenv("API_KEY")

The scanner verifies whether these variables are ever logged or exposed through admin endpoints.

middleBrick's CORS analysis module specifically tests Chi applications for overly permissive CORS configurations that might allow API key exposure to malicious front-end applications. The scanner attempts cross-origin requests to see if API key headers are accessible.

Rate limiting analysis in middleBrick examines Chi's rate limiting middleware to identify whether it reveals information about API key validity through timing or error responses. The scanner attempts requests with various key patterns to identify information leakage.

The scanner also tests Chi's session management for API key fixation vulnerabilities. It examines how API keys are stored in sessions and whether they're properly rotated or invalidated after use.

middleBrick's LLM security module specifically tests for API key exposure in AI-related endpoints, which is particularly relevant for modern Chi applications that might integrate with language models. The scanner tests for prompt injection attacks that could extract API keys from system prompts or responses.

Remediating API key exposure in Chi applications requires implementing framework-specific security patterns that leverage Chi's middleware architecture effectively. The following approaches address the unique exposure vectors in Chi applications.

First, implement proper API key sanitization middleware. This middleware should intercept API keys from headers and either redact them or store them in a secure context that prevents logging:

func secureAPIKeyMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Extract and sanitize API key
        authHeader := r.Header.Get("Authorization")
        if strings.HasPrefix(authHeader, "Bearer ") {
            // Store sanitized version
            ctx := context.WithValue(r.Context(), "api_key", "REDACTED")
            r = r.WithContext(ctx)
        }
        next.ServeHTTP(w, r)
    })
}

// Use in middleware chain
router.Use(secureAPIKeyMiddleware)

This middleware ensures that even if logging occurs, the actual API key values are never exposed.

Implement proper error handling that never includes sensitive data in responses. Chi's error handling middleware should catch all panics and errors, sanitize any request data, and return generic error messages:

func secureErrorMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        defer func() {
            if err := recover(); err != nil {
                log.Printf("Recovered panic: %v", err)
                http.Error(w, "Internal Server Error", http.StatusInternalServerError)
            }
        }()
        next.ServeHTTP(w, r)
    })
}

For route parameter handling, implement strict validation and sanitization. Chi's path parameters should never directly contain API keys:

func validateAPIKeys(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Check if API key is in URL path (vulnerable pattern)
        path := r.URL.Path
        if strings.Contains(path, "api_key=") || strings.Contains(path, "key=") {
            http.Error(w, "Invalid request format", http.StatusBadRequest)
            return
        }
        next.ServeHTTP(w, r)
    })
}

Environment variable handling should use secure configuration patterns. Instead of directly accessing environment variables in handlers, use a configuration struct that's properly sanitized:

type Config struct {
    APIKey string `json:"api_key"`
}

var config Config

func init() {
    // Load config securely
    config.APIKey = os.Getenv("API_KEY")
    if config.APIKey == "" {
        log.Fatal("API_KEY environment variable not set")
    }
    
    // Immediately redact from logs
    config.APIKey = "REDACTED"
}

Implement CORS policies that prevent API key exposure to malicious origins:

func corsMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Access-Control-Allow-Origin", "https://yourdomain.com")
        w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
        w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
        
        // Don't expose sensitive headers
        w.Header().Set("Access-Control-Expose-Headers", "")
        
        next.ServeHTTP(w, r)
    })
}

For rate limiting, implement patterns that don't reveal API key validity:

func secureRateLimit(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Use constant-time comparisons
        apiKey := r.Header.Get("Authorization")
        if apiKey != "" {
            // Always perform rate limit check, even for invalid keys
            // This prevents timing attacks that reveal key validity
            rateLimitCheck(apiKey)
        }
        next.ServeHTTP(w, r)
    })
}

Implement proper session management that rotates API keys:

func rotateAPIKey(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Check for existing API key in session
        session, _ := store.Get(r, "session")
        
        // If key exists, rotate it
        if key, exists := session.Values["api_key"]; exists {
            // Generate new key and invalidate old one
            newKey := generateAPIKey()
            session.Values["api_key"] = newKey
            session.Save(r, w)
            
            // Update context with new key
            ctx := context.WithValue(r.Context(), "api_key", newKey)
            r = r.WithContext(ctx)
        }
        
        next.ServeHTTP(w, r)
    })
}

Finally, implement comprehensive logging that never includes sensitive data. Use structured logging with proper field redaction:

type secureLogger struct {
    logger *log.Logger
}

func (s *secureLogger) Printf(format string, v ...interface{}) {
    // Redact API keys from logs
    for i, val := range v {
        if str, ok := val.(string); ok && isPotentialAPIKey(str) {
            v[i] = "REDACTED"
        }
    }
    s.logger.Printf(format, v...)
}

func isPotentialAPIKey(s string) bool {
    // Simple heuristic to detect API keys
    return len(s) > 20 && (strings.Contains(s, "-") || strings.Contains(s, "_"))
}