Bola Idor in Chi with Jwt Tokens

Broken Object Level Authorization (BOLA) in the context of Chi with JWT tokens occurs when an API endpoint in a Chi application uses JWTs for identity but fails to enforce proper resource ownership checks on the server side. Chi is a lightweight HTTP web framework for the Go ecosystem, and JWTs are commonly used for stateless authentication. The vulnerability arises when an authenticated user can manipulate resource identifiers—such as a numeric ID in a URL—and the server trusts that identifier without verifying that the resource belongs to the subject represented by the JWT.

For example, consider a Chi endpoint defined with a route parameter /users/{userID}. The JWT may contain a sub claim identifying the user, but if the handler retrieves the userID from the URL and directly fetches or modifies that record without comparing it to the sub claim, an attacker can change the userID to access or modify another user’s data. This is BOLA because authorization is missing: authentication via JWT confirms who the user is, but not whether that user is allowed to access the specific object they are requesting.

The risk is compounded when endpoints expose sensitive fields or operations without scoping by subject. Chi applications that decode a JWT to extract claims but then pass the raw identifier to service or repository layers without ownership validation enable horizontal privilege escalation. For instance, an attacker authenticated with their own JWT could increment an integer ID to enumerate and access other users’ profiles, settings, or administrative functions. Because Chi does not enforce any built-in authorization, developers must explicitly implement these checks; omitting them results in a classic BOLA flaw.

Such vulnerabilities map to the OWASP API Top 10 (2023) category A01:2023 — Broken Object Level Authorization. Real-world examples include scenarios where JWTs contain user roles or tenant IDs but the API does not validate that the requested resource aligns with those claims. In multi-tenant systems, missing tenant checks alongside JWT-based authentication can lead to cross-tenant data access. Because Chi routes are minimal and explicit, developers have full control, but they must ensure every handler that uses a resource identifier validates it against the authenticated subject to prevent BOLA.

An attacker flow might involve obtaining a valid JWT through normal login, then interacting with a Chi endpoint that exposes object IDs. By modifying the ID in the request and observing differences in responses—such as data returned, HTTP status codes, or error messages—an attacker can map accessible objects and perform unauthorized actions. Because the JWT remains valid, the server does not reject the request, but the missing authorization check allows the operation to succeed. This illustrates why JWTs alone are insufficient for object-level protection and why Chi endpoints must enforce subject-to-object mapping explicitly.

In summary, BOLA in Chi with JWT tokens emerges when authentication identifies a user but authorization does not bind the requested resource to that user. The framework’s flexibility means developers must consciously scope every data access operation to the claims in the JWT, typically by comparing a resource owner ID or tenant identifier from the token to the ID in the request. Without this, the API remains vulnerable to horizontal privilege escalation and data exposure despite using JWT-based authentication.

To remediate BOLA in Chi when using JWT tokens, ensure that every handler that accesses a resource validates the resource’s ownership or tenant scope against the claims in the JWT. This involves decoding the token, extracting a subject or tenant identifier, and using it to filter database queries or object lookups. Below are concrete code examples demonstrating secure patterns in Chi.

First, decode the JWT in a Chi middleware or handler and attach claims to the request context. Then, in resource-handling endpoints, extract the identifier from the route and compare it to the subject from the token before proceeding.

import (  
    "context"  
    "net/http"  
    "strconv"  

    "github.com/go-chi/chi/v5"  
    "github.com/golang-jwt/jwt/v5"  
)

// JWTClaims holds custom claims including a subject identifier.
type JWTClaims struct {  
    Subject string `json:"sub"`  
    jwt.RegisteredClaims  
}

// authMiddleware validates the JWT and injects claims into context.
func authMiddleware(next http.Handler) http.Handler {  
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {  
        tokenString := /* extract token from header */  
        claims := &JWTClaims{}  
        token, err := jwt.ParseWithClaims(tokenString, claims, func(token *jwt.Token) (interface{}, error) {  
            /* return your key function */  
            return []byte("your-secret"), nil  
        })  
        if err != nil || !token.Valid {  
            http.Error(w, "unauthorized", http.StatusUnauthorized)  
            return  
        }  
        ctx := context.WithValue(r.Context(), "claims", claims)  
        next.ServeHTTP(w, r.WithContext(ctx))  
    })  
}

// userHandler is a Chi route that enforces BOLA by comparing resource ID to subject.
func userHandler(w http.ResponseWriter, r *http.Request) {  
    claims, ok := r.Context().Value("claims").(*JWTClaims)  
    if !ok {  
        http.Error(w, "unauthorized", http.StatusUnauthorized)  
        return  
    }  

    userID, err := strconv.Atoi(chi.URLParam(r, "userID"))  
    if err != nil {  
        http.Error(w, "bad request", http.StatusBadRequest)  
        return  
    }  

    // Enforce BOLA: ensure the requested userID matches the subject in the JWT.
    if claims.Subject == "" || userID != parseSubjectID(claims.Subject) {  
        http.Error(w, "forbidden", http.StatusForbidden)  
        return  
    }  

    // Proceed to fetch or update the user resource knowing the subject matches.
    // Example: user, err := store.GetUserByID(userID)  
    w.Write([]byte("user profile"))  
}

// parseSubjectID converts a subject claim (e.g., "user:123") to an integer ID.
func parseSubjectID(sub string) int {  
    // Simplified parsing; adapt to your subject format.
    // In practice, use a consistent format like "user:123" and split.
    return 123 // placeholder
}

For endpoints that operate on collections or where subjects map to tenants, embed the subject or tenant ID in the query filter. For example, when listing resources, always scope by the subject:

// listUserResources returns only resources belonging to the subject.
func listUserResources(w http.ResponseWriter, r *http.Request) {  
    claims, ok := r.Context().Value("claims").(*JWTClaims)  
    if !ok {  
        http.Error(w, "unauthorized", http.StatusUnauthorized)  
        return  
    }  

    subjectID := parseSubjectID(claims.Subject)  
    // Example: rows, err := db.Query("SELECT * FROM resources WHERE owner_id = ?", subjectID)  
    // Ensure the query filters by owner_id or tenant_id derived from the JWT.
    w.Write([]byte("resources list"))  
}

Additionally, validate JWT claims for roles or scopes if your authorization model requires it, but always pair role checks with object ownership. Avoid trusting URL parameters alone; derive identifiers from the JWT or ensure the parameter is verified against the subject before any data access. Using Chi’s middleware chain, you can enforce this pattern consistently across routes, reducing the risk of BOLA despite the presence of JWT tokens.

• How does middleBrick handle BOLA in Chi with JWT tokens?

  middleBrick runs black-box scans that test unauthenticated and authenticated surfaces, including JWT-based endpoints. It checks whether resource identifiers are scoped to the authenticated subject and reports missing ownership checks with severity-ranked findings and remediation guidance.

• Can middleBrick map findings to compliance frameworks for Chi APIs using JWTs?

  Yes. Findings include mappings to frameworks such as OWASP API Top 10, PCI-DSS, SOC2, HIPAA, and GDPR, helping you understand how BOLA and JWT-related issues align with common compliance requirements.