Broken Access Control in Buffalo with Bearer Tokens

Broken Access Control occurs when authorization checks are missing or incorrectly enforced, allowing a user to access functionality or data they should not be able to reach. In the Buffalo framework, this risk is amplified when APIs rely solely on Bearer Tokens for authentication without properly validating scopes, roles, or resource ownership.

Buffalo does not enforce authorization by default. If you add Bearer Token validation at the middleware level but skip per-route authorization checks, an authenticated user can change IDs in URLs (BOLA/IDOR) or escalate privileges horizontally/vertically. For example, an API endpoint like /api/v1/organizations/:org_id/members might verify a valid Bearer Token but fail to confirm that the token’s subject has permission to view or modify the given org_id. This mismatch between authentication (token is valid) and authorization (subject lacks rights for that org) is a classic Broken Access Control scenario.

When Bearer Tokens carry role or scope claims, developers might assume those claims alone are sufficient. However, if the application does not re-check those claims per request against the target resource, access control can be bypassed. An attacker who obtains a low-privilege Bearer Token could manipulate request parameters to access admin-only endpoints if the server does not validate scope/role on each operation. Buffalo’s habitability and parameter parsing features can inadvertently expose IDs if developers forget to apply policy checks before using them in queries.

Additionally, if token validation is performed inconsistently—say, enforced on some routes but omitted on others—an attacker can pivot to unprotected endpoints. A missing authorization check on a bulk-export route, combined with predictable IDs and a valid Bearer Token, can lead to mass data exposure. Because Buffalo encourages rapid prototyping, it’s easy to omit authorization middleware on new routes, unintentionally widening the attack surface.

To detect this with middleBrick, scans run against the unauthenticated attack surface and authenticated-style probes (using Bearer Tokens) to compare authentication versus authorization enforcement. Findings highlight endpoints where tokens are accepted but role/scope/resource-level checks are absent, mapping to OWASP API Top 10 (2023) A01: Broken Access Control and supporting compliance frameworks like PCI-DSS and SOC2.

Remediation focuses on ensuring every request that accesses or modifies a resource validates not only the Bearer Token but also the token’s permissions and the target resource’s ownership or scope. Below are concrete, idiomatic examples for Buffalo.

1. Validate Bearer Token and enforce scope/role per route

Use a custom authorization middleware that decodes the Bearer Token, extracts scopes or roles, and checks them before invoking the handler.

// app/middleware/auth_required.go
package middleware

import (
    "net/http"
    "strings"

    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo/middleware"
    "github.com/golang-jwt/jwt/v5"
)

func AuthRequired(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        auth := c.Request().Header.Get("Authorization")
        if auth == "" {
            return c.Error(http.StatusUnauthorized, "missing authorization header")
        }
        parts := strings.Split(auth, " ")
        if len(parts) != 2 || parts[0] != "Bearer" {
            return c.Error(http.StatusUnauthorized, "invalid authorization header format")
        }
        tokenString := parts[1]
        token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
            // TODO: use your actual key retrieval, e.g., jwt.ParseWithClaims
            return []byte("your-secret-key"), nil
        })
        if err != nil || !token.Valid {
            return c.Error(http.StatusUnauthorized, "invalid token")
        }
        // Ensure claims contain required scope/role
        if claims, ok := token.Claims.(jwt.MapClaims); ok {
            if scopes, ok := claims["scope"].(string); !ok || !strings.Contains(scopes, "read:orgs") {
                return c.Error(http.StatusForbidden, "insufficient scope")
            }
            // optionally set current user in context
            c.Set("user_id", claims["sub"])
        }
        return next(c)
    }
}

Then in app/app.go, add the middleware globally or to specific routes:

// app/app.go
func App() *buffalo.App {
    app := buffalo.New(buffalo.Options{})
    app.Use(middleware.Session)
    app.Use(middleware.Params)
    app.Use(middleware.Transaction)
    app.Use(middleware.AuthRequired) // applies to all routes

    // or apply selectively:
    // app.GET("/api/organizations/:org_id/members", MyHandler, middleware.AuthRequired)
    return app
}

2. Enforce resource-level ownership checks in handlers

After authentication, verify that the subject of the token can access the resource identified by org_id or any other entity.

// app/handlers/org_members.go
package handlers

import (
    "net/http"

    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/pop/v6"
)

func OrgMembersList(c buffalo.Context) error {
    orgID := c.Param("org_id")
    userID := c.Get("user_id") // set by AuthRequired middleware

    // Perform membership check: ensure user is a member of orgID
    var membership OrganizationMembership
    err := pop.Transaction(func(tx *pop.Connection) error {
        return tx.Where("user_id = ? AND org_id = ?", userID, orgID).First(&membership)
    })
    if err != nil {
        return c.Error(http.StatusForbidden, "access denied to this organization")
    }

    // Proceed if authorized
    var members []Member
    if err := tx.All(&members); err != nil {
        return c.Error(http.StatusInternalServerError, err.Error())
    }
    return c.Render(http.StatusOK, r.JSON(members))
}

3. Apply scope-based checks for sensitive operations

For endpoints that modify data, require specific scopes and ensure they are checked against the action.

// app/handlers/org_update.go
package handlers

import (
    "net/http"

    "github.com/gobuffalo/buffalo"
)

func OrgUpdate(c buffalo.Context) error {
    auth := c.Request().Header.Get("Authorization")
    parts := strings.Split(auth, " ")
    tokenString := parts[1]
    token, _ := jwt.Parse(tokenString, keyFunc)
    if claims, ok := token.Claims.(jwt.MapClaims); ok {
        scopes := claims["scope"]
        if !strings.Contains(scopes, "write:orgs") {
            return c.Error(http.StatusForbidden, "missing write:orgs scope")
        }
    }
    // proceed with update logic
    return nil
}

These patterns ensure that authentication via Bearer Tokens is coupled with proper authorization checks, mitigating Broken Access Control in Buffalo applications.