Broken Access Control in Fiber (Go)

Broken Access Control is a top-ten API risk under the OWASP API Security Top 10 and commonly surfaces in APIs built with Fiber and Go. When authorization checks are missing, incomplete, or bypassed, attackers can access or modify resources that should be restricted, such as other users' data or admin-only endpoints.

In Go, developers often use Fiber’s flexible grouping and middleware features to organize routes. However, if route-level authorization is not enforced consistently across groups or if middleware does not validate subject attributes (roles, scopes, tenant IDs), access control can break in subtle ways. For example, an admin-only route might rely solely on a client-supplied role claim in the JWT without verifying that the claim is still valid and hasn’t been tampered with. Because Fiber allows easy route prefixing and shared middleware, it’s possible to accidentally expose an unauthenticated or weakly protected group that should have required specific scopes or roles.

Additionally, Go’s strong typing and static compilation can give a false sense of safety. Developers may assume that because a handler parameter is typed, access control is enforced, but without explicit checks, any authenticated user might reach sensitive handlers. Consider a multi-tenant API where a handler uses a path parameter like userID. If the handler does not compare the authenticated user’s ID to the userID in the request, a BOLA/IDOR issue arises—this is an access control breakdown that can be introduced regardless of the framework but is easy to miss when routes are organized as groups in Fiber.

The interaction between JWT validation middleware and route-specific authorization in Fiber can also create issues. If a developer attaches a JWT parser middleware to a group and then adds role checks only on a subset of handlers, endpoints without those checks become accessible to users who shouldn’t have permission. In Go, it’s idiomatic to chain middlewares, but if authorization is not enforced on every handler or group, the attack surface expands. This is especially risky when using public OpenAPI specs with $ref resolution, because unchecked paths revealed by the spec can be exercised directly.

Consider a realistic scenario: an endpoint GET /users/me relies on a middleware that sets the user from a token, but a sibling route GET /users/:id within the same group lacks a check that the authenticated user owns the requested ID. An attacker can enumerate IDs and access other users’ data. Because Fiber allows defining multiple groups with different middlewares, it’s important to verify that each group and each handler applies the correct authorization logic, not just authentication.

middleBrick scans such unauthenticated attack surfaces and flags these authorization gaps among its 12 security checks. It cross-references the runtime behavior with the OpenAPI spec (including full $ref resolution) to highlight paths where access controls are missing or misconfigured, providing findings mapped to OWASP API Top 10 and guidance for remediation.

To remediate Broken Access Control in Fiber with Go, enforce authorization checks on every handler that accesses user-specific or privileged resources. Prefer centralized group middleware for common authorization patterns and validate all inputs against the authenticated subject. Below are concrete, idiomatic examples.

1. Require ownership check for user-specific endpoints

Ensure a user can only access their own data by comparing the authenticated subject to the requested identifier.

package main

import (
    "github.com/gofiber/fiber/v2"
    "github.com/gofiber/fiber/v2/middleware/jwt"
)

type Claims struct {
    UserID string `json:"user_id"`
    Role   string `json:"role"`
}

func main() {
    app := fiber.New()

    // JWT auth middleware attached to a protected group
    protected := app.Group("/api")
    protected.Use(jwt.New(jwt.Config{
        SigningKey: []byte("your-secret-key"),
    }))

    // Handler that safely checks ownership
    protected.Get("/users/:id", func(c *fiber.Ctx) error {
        claims := c.Locals("user").(*jwt.Token).Claims().(*Claims)
        userID := c.Params("id")
        if claims.UserID != userID {
            return c.Status(fiber.StatusForbidden).SendString("access denied: cannot access other users")
        }
        // proceed with safe, owner-specific logic
        return c.JSON(fiber.Map{ "message": "ok", "userID": userID })
    })

    app.Listen(":3000")
}

2. Role- and scope-based authorization on admin routes

Use group middleware to enforce role checks for admin-only endpoints, rather than relying on client claims alone.

func requireAdmin(c *fiber.Ctx) error {
    claims := c.Locals("user").(*jwt.Token).Claims().(*Claims)
    if claims.Role != "admin" {
        return c.Status(fiber.StatusForbidden).SendString("admin only")
    }
    return c.Next()
}

func main() {
    app := fiber.New()

    admin := app.Group("/admin")
    admin.Use(requireAdmin)
    admin.Get("/dashboard", func(c *fiber.Ctx) error {
        return c.JSON(fiber.Map{ "admin": true })
    })

    // Public endpoint for comparison
    app.Get("/health", func(c *fiber.Ctx) error {
        return c.SendString("healthy")
    })

    app.Listen(":3000")
}

3. Apply authorization to every handler in a group

When using Fiber groups, avoid attaching authentication but skipping authorization on some handlers. If a group represents a sensitive domain, require explicit checks on each handler or use a shared authorization middleware.

func requireScope(c *fiber.Ctx) error {
    claims := c.Locals("user").(*jwt.Token).Claims().(*Claims)
    // Assume scopes are stored as a comma-separated string in a custom claim
    // Validate required scope for this group
    // This is a simplified check; in production, parse scopes into a map or set
    if !hasScope(claims.Scopes, "read:reports") {
        return c.Status(fiber.StatusForbidden).SendString("insufficient scope")
    }
    return c.Next()
}

func hasScope(scopes, required string) bool {
    // naive example; use a proper scope set in real code
    return scopes == required
}

func main() {
    app := fiber.New()

    reports := app.Group("/reports")
    reports.Use(requireScope)
    reports.Get("/summary", func(c *fiber.Ctx) error {
        return c.JSON(fiber.Map{ "summary": "data" })
    })

    app.Listen(":3000")
}

4. Validate and normalize IDs from path parameters

Avoid treating path parameters as trusted. Parse and validate IDs before using them in queries or comparisons to prevent ID manipulation attacks.

import "strconv"

func getUser(c *fiber.Ctx) error {
    id, err := strconv.Atoi(c.Params("id"))
    if err != nil || id <= 0 {
        return c.Status(fiber.StatusBadRequest).SendString("invalid user ID")
    }
    // fetch user by id with proper validation
    return c.JSON(fiber.Map{ "id": id })
}

5. Use centralized middleware and avoid per-handler omissions

Define reusable authorization middlewares for common patterns (ownership, role, scope) and apply them consistently across groups to reduce the risk of accidental misconfiguration.

func requireTenantUser(c *fiber.Ctx) error {
    tenantID := c.Params("tenantId")
    user := c.Locals("user").(*jwt.Token).Claims().(*Claims)
    if user.TenantID != tenantID {
        return c.Status(fiber.StatusForbidden).SendString("cross-tenant access not allowed")
    }
    return c.Next()
}

func main() {
    app := fiber.New()

    tenants := app.Group("/tenants/:tenantId")
    tenants.Use(requireTenantUser)
    tenants.Get("/profile", func(c *fiber.Ctx) error {
        return c.JSON(fiber.Map{ "tenant": c.Params("tenantId") })
    })

    app.Listen(":3000")
}

By pairing Fiber’s route grouping with explicit, per-handler authorization and careful input validation, you reduce the likelihood of Broken Access Control. middleBrick complements these practices by scanning your endpoints and surfacing authorization gaps across your API surface.