Double Free in Chi with Api Keys

Double Free is a memory safety vulnerability that occurs when a program attempts to free the same block of allocated memory twice. In the context of Chi, a common Go HTTP router, this risk can emerge when API key handling logic interacts with request-scoped contexts and response writers. If middleware allocates resources to validate or attach API key metadata to a request and later deallocates or reuses that memory without guarding against repeated free operations, memory corruption can occur. This is particularly relevant when key validation produces dynamic objects (e.g., parsed claims or cached key metadata) that are stored in request context and later released.

Consider a Chi route where an API key is extracted from a header, validated against a store, and then attached to the request context. If the validation step allocates a struct to hold key metadata and both the context cleanup and an explicit response-handler path attempt to free that struct, a Double Free can manifest under certain failure conditions (e.g., early error returns combined with deferred cleanup). The unauthenticated attack surface tested by middleBrick can expose such patterns when API key validation logic is exercised across multiple security checks, including Input Validation and Unsafe Consumption. Real-world attack patterns like improper error handling or race conditions in key processing may amplify the risk, potentially leading to crashes or memory manipulation.

middleBrick’s 12 parallel security checks analyze the unauthenticated endpoints, including OpenAPI/Swagger spec analysis with full $ref resolution, to detect risky behaviors around authentication and data handling. While Double Free is a low-level concern, its presence can undermine the integrity of API key workflows. The LLM/AI Security checks do not target memory safety directly, but the scanner’s focus on authentication and property authorization helps highlight endpoints where key handling logic may interact with complex request lifecycle management, increasing the chance of unsafe memory patterns when code paths are not carefully synchronized.

To illustrate, here is a realistic example of API key extraction and validation in Chi that, if mismanaged, could contribute to unsafe memory patterns (note: this is illustrative for educational purposes and not a guaranteed Double Free trigger):

package main

import (
	"context"
	"net/http"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
)

type keyMetadata struct {
	KeyID string
	Scopes []string
}

func extractAPIKey(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		key := r.Header.Get("X-API-Key")
		if key == "" {
			http.Error(w, "missing api key", http.StatusUnauthorized)
			return
		}
		// Simulate validation that allocates metadata
		meta := &keyMetadata{
			KeyID: key,
			Scopes: []string{"read", "write"},
		}
		ctx := context.WithValue(r.Context(), "keyMeta", meta)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

func main() {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(extractAPIKey)
	r.Get("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("ok"))
	})
	http.ListenAndServe(":8080", r)
}

Remediation for Double Free risks in Chi when working with API keys focuses on eliminating unsafe memory reuse and ensuring deterministic cleanup. Since Go manages memory automatically, Double Free typically arises from patterns where manual resource management logic interacts with Go’s runtime, such as using finalizers or unsafe pointers. To keep API key handling safe, avoid retaining references that could be double-released through context manipulation or deferred functions that run on multiple paths.

A robust approach is to keep key metadata lightweight and avoid storing pointers to mutable state in request context when possible. If you must store metadata, ensure a single clear ownership path and do not explicitly free memory; rely on Go’s garbage collector. Use context cancellation to signal completion, and structure handlers so that deferred cleanups are idempotent and guard against repeated execution. The following example demonstrates a safer pattern for API key validation in Chi:

package main

import (
	"context"
	"net/http"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
)

type keyMetadata struct {
	KeyID string
	Scopes []string
}

// Safe extractor: attaches metadata without complex lifecycle control.
func attachAPIKey(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		key := r.Header.Get("X-API-Key")
		if key == "" {
			http.Error(w, "missing api key", http.StatusUnauthorized)
			return
		}
		// Perform validation (e.g., lookup) without retaining unnecessary pointers.
		// For demonstration, we keep metadata simple and avoid finalizers.
		meta := &keyMetadata{
			KeyID: key,
			Scopes: []string{"read"},
		}
		// Use context.WithValue sparingly; prefer structured keys to avoid collisions.
		ctx := context.WithValue(r.Context(), struct{}{}, meta)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// Ensure handlers do not trigger multiple cleanups on the same context-derived data.
func helloHandler(w http.ResponseWriter, r *http.Request) {
	// Retrieve metadata safely; no explicit deletion or double-release logic.
	if meta, ok := r.Context().Value(struct{}{}).(*keyMetadata); ok {
		if !contains(meta.Scopes, "read") {
			http.Error(w, "insufficient scope", http.StatusForbidden)
			return
		}
		w.Write([]byte("access granted"))
		return
	}
	http.Error(w, "invalid internal state", http.StatusInternalServerError)
}

func contains(slice []string, item string) bool {
	for _, s := range slice {
		if s == item {
			return true
		}
	}
	return false
}

func main() {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(attachAPIKey)
	r.Get("/", helloHandler)
	http.ListenAndServe(":8080", r)
}

Additional remediation practices include:

• Validate API keys early and avoid deferred functions that might execute multiple times on the same request context.
• Use middleBrick’s Authentication and Property Authorization checks to verify that key handling logic does not introduce unsafe state transitions.
• Leverage the CLI (middlebrick scan <url>) and GitHub Action to continuously monitor endpoints for risky patterns, ensuring that changes to key management do not reintroduce vulnerabilities.