Denial Of Service in Chi with Api Keys

A Denial of Service (DoS) scenario in the context of Chi API routes combined with API key usage can manifest when rate limiting or request validation is insufficient, allowing a single client to consume disproportionate server resources. When API keys are accepted but not properly validated for quota or misuse, an attacker may repeatedly call a computationally expensive endpoint, effectively degrading service for legitimate users.

Consider an endpoint that performs heavy data aggregation or uses large JSON payloads. If the route is defined in Chi without explicit limits on requests per API key, an unauthenticated or authenticated attacker can send many requests per second. Even when API keys are required, missing or weak enforcement of rate limits means the server continues processing each request, increasing CPU, memory, and connection usage until the service becomes unresponsive.

In a Chi-based service, routes are typically structured as middleware chains. Without a dedicated rate limiting check tied to the API key, each request proceeds through the middleware stack, including parsing and business logic. This can trigger resource exhaustion, especially if the handler performs operations such as database queries or external HTTP calls. The API key itself does not mitigate this; it may simply identify the client without throttling behavior.

Furthermore, if the API key is exposed in logs or error messages during high-volume attacks, it may aid reconnaissance. The combination of a known Chi endpoint, a valid API key, and missing DoS protections creates a scenario where availability is compromised. This aligns with common OWASP API Top 10 risks such as excessive resource consumption, where attackers exploit inadequate rate limiting and lack of quotas.

middleBrick scans for Rate Limiting and Data Exposure as part of its 12 security checks, helping to identify missing protections around API key usage and DoS vectors. It evaluates endpoints for missing throttling mechanisms and checks whether responses inadvertently expose identifiers that could be leveraged in follow-up attacks.

To remediate DoS risks when using API keys in Chi, enforce rate limiting per API key and validate keys before entering expensive middleware. Below are concrete examples demonstrating how to implement these controls effectively.

1. Rate limiting per API key in Chi

Use a middleware that tracks request counts per key and rejects excess requests. Here is an example using a simple in-memory map and a token bucket approach. For production, consider a distributed store like Redis.

import chi "github.com/go-chi/chi/v5"
import "net/http"
import "sync"
import "time"

var (
    limits = make(map[string]int)
    mu     sync.Mutex
)

func apiKeyRateLimit(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        apiKey := r.Header.Get("X-API-Key")
        if apiKey == "" {
            http.Error(w, "Forbidden: missing API key", http.StatusForbidden)
            return
        }
        mu.Lock()
        count, now := limits[apiKey], time.Now()
        // Reset every minute
        // In practice, use a more robust rate limiter or external store
        // This is a minimal illustration
        if now.Minute() != (now.Unix() / 60) {
            limits[apiKey] = 1
            mu.Unlock()
        } else {
            if count > 100 { // 100 requests per minute per key
                mu.Unlock()
                http.Error(w, "Too Many Requests", http.StatusTooManyRequests)
                return
            }
            limits[apiKey] = count + 1
            mu.Unlock()
        }
        next.ServeHTTP(w, r)
    })
}

func handler(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("OK"))
}

func main() {
    r := chi.NewRouter()
    r.Use(apiKeyRateLimit)
    r.Get("/data", handler)
    http.ListenAndServe(":8080", r)
}

2. Validate API key before heavy processing

Ensure the API key is verified early in the middleware chain to avoid unnecessary work. This example shows a basic key validation handler in Chi.

import chi "github.com/go-chi/chi/v5"
import "net/http"

func validateAPIKey(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        apiKey := r.Header.Get("X-API-Key")
        // Replace with actual validation against a store
        if !isValidKey(apiKey) {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        next.ServeHTTP(w, r)
    })
}

func isValidKey(key string) bool {
    // Example: check against a map or external service
    validKeys := map[string]bool{
        "abc123": true,
        "def456": true,
    }
    return validKeys[key]
}

func expensiveHandler(w http.ResponseWriter, r *http.Request) {
    // Simulate expensive work
    w.Write([]byte("Processed"))
}

func main() {
    r := chi.NewRouter()
    r.Use(validateAPIKey)
    r.Post("/expensive", expensiveHandler)
    http.ListenAndServe(":8080", r)
}

These patterns help mitigate DoS by tying rate limits to API keys and ensuring keys are validated before resource-intensive logic runs. For broader protection, combine these with infrastructure-level throttling and monitoring.

middleBrick’s CLI can be used to verify that your endpoints enforce these controls. Run middlebrick scan <url> to generate a report that highlights missing rate limiting and other DoS-related findings.