Insecure Design in Chi (Go)

Insecure Design in the context of a Chi-based Go service occurs when application architecture and routing decisions do not enforce authorization boundaries or assume trust in path parameters and user-supplied data. Chi is a lightweight, idiomatic router, but it does not enforce authentication or authorization by itself; that responsibility falls to the developer. When routes are defined with permissive patterns or middleware is omitted, attackers can manipulate identifiers in URLs to access other users' resources, leading to Insecure Design and related authorization flaws such as BOLA/IDOR.

Consider a Chi route that captures an integer user identifier without validating ownership or enforcing access control at the routing or handler level:

r.Get("/users/{userID}", func(w http.ResponseWriter, r *http.Request) {
    userIDStr := chi.URLParam(r, "userID")
    // No check that the authenticated user owns userIDStr
    // Directly using userIDStr to query a database or return data
})

If the API does not cross-reference the authenticated subject with the {userID} in the path, an attacker can change the ID and enumerate or modify other users' data. This is a classic Insecure Design pattern where the endpoint design lacks authorization checks, enabling BOLA/IDOR. Similarly, endpoints that accept IDs in the URL without verifying that the requesting user has permission to perform the requested action (such as deleting or updating) expose an insecure design that can lead to privilege escalation.

Input validation gaps also stem from insecure design. If route parameters are not validated for type, range, or format, an attacker can supply malicious payloads that cause unexpected behavior. For example, failing to validate that an ID is numeric or within expected bounds can lead to injection or data exposure when those values are used in downstream queries without safeguards. In a Go Chi service, this means not only validating input but also ensuring that the routing structure does not implicitly trust any part of the request.

Design-time decisions such as exposing internal identifiers in URLs, lacking per-endpoint authentication requirements, or not segmenting administrative vs user endpoints contribute to an insecure design. Without middleware that enforces authentication and authorization consistently, Chi routes can inadvertently expose sensitive functionality. The use of OpenAPI specifications can help surface these risks by aligning documented routes with required security schemes, but the implementation must still enforce checks at the handler or middleware layer.

To detect these issues, scanners perform unauthenticated and authenticated checks, testing endpoints with modified identifiers and observing whether access controls are respected. They correlate route definitions with runtime behavior to highlight missing authorization enforcement and improper data exposure, which are rooted in insecure design choices rather than implementation bugs alone.

Remediation centers on enforcing authentication and authorization before accessing resources, validating all route parameters, and designing routes with least privilege in mind. In Go with Chi, use middleware to validate the authenticated user and ensure that any identifier in the URL is scoped to that user.

First, implement a middleware that extracts and validates ownership or permissions before the handler runs:

func AuthUser(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        userIDStr := chi.URLParam(r, "userID")
        // authenticatedUser is derived from session or token
        authenticatedUser := r.Context().Value("userID")
        if authenticatedUser != userIDStr {
            http.Error(w, "forbidden", http.StatusForbidden)
            return
        }
        next.ServeHTTP(w, r)
    })
}

Then apply this middleware to routes that handle user-specific data:

r.Group(func(r chi.Router) {
    r.Use(AuthUser)
    r.Get("/users/{userID}", func(w http.ResponseWriter, r *http.Request) {
        userID := chi.URLParam(r, "userID")
        // Safe to proceed because AuthUser ensures ownership
        // Fetch and return user data
    })
})

For endpoints that perform actions beyond read, such as updates or deletions, enforce additional checks and use method-specific middleware:

func RequireScope(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Verify token scopes or roles here
        if !hasScope(r, "users:write") {
            http.Error(w, "insufficient scope", http.StatusForbidden)
            return
        }
        next.ServeHTTP(w, r)
    })
}

Validate inputs rigorously before using them in queries or business logic:

func ValidateUserParam(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        userIDStr := chi.URLParam(r, "userID")
        var userID int64
        if _, err := fmt.Sscanf(userIDStr, "%d", &userID); err != nil || userID <= 0 {
            http.Error(w, "bad request", http.StatusBadRequest)
            return
        }
        ctx := context.WithValue(r.Context(), "validatedUserID", userID)
        next.ServeHTTP(w, r.WithContext(ctx))
    })
}

Combine these middlewares to create a secure route pipeline that addresses Insecure Design by ensuring that every request is authenticated, authorized, and validated before any data access occurs. This approach reduces the attack surface and aligns route design with security best practices.