Zone Transfer in Fiber

Zone Transfer vulnerabilities in Fiber applications typically emerge through improper authorization checks on API endpoints that expose user or tenant-specific data. In Fiber, this manifests when endpoints iterate over collections of resources without verifying the requesting user's ownership or permissions for each item.

A common pattern occurs in list endpoints where developers fetch all items and rely on client-side filtering. Consider a Fiber application managing multi-tenant resources:

app.GET("/api/tenants/:tenantID/resources", func(c *fiber.Ctx) error {
    tenantID := c.Params("tenantID")
    
    // Vulnerable: fetches ALL resources without tenant scoping
    resources := ResourceStore.GetAll()
    
    return c.JSON(resources)
})

An attacker can exploit this by enumerating tenant IDs. If tenant IDs are predictable (like sequential integers or UUIDs), an attacker can systematically request /api/tenants/1/resources, /api/tenants/2/resources, etc., accessing data across all tenants.

Another Fiber-specific manifestation appears in GraphQL resolvers or middleware that cache data at the application level. If a resolver fetches data without tenant isolation:

app.Use(func(c *fiber.Ctx) error {
    // Context-based tenant detection
    tenantID := c.Get("X-Tenant-ID")
    c.Locals("tenantID", tenantID)
    return c.Next()
})

app.GET("/api/resources", func(c *fiber.Ctx) error {
    // Vulnerable: context tenantID not used in query
    resources := db.Query("SELECT * FROM resources")
    return c.JSON(resources)
})

The vulnerability becomes critical when combined with Fiber's middleware chain. If authentication middleware sets tenant context but subsequent handlers ignore it, zone transfer becomes trivial. Attackers can also exploit predictable resource identifiers in RESTful URLs:

app.GET("/api/resources/:id", func(c *fiber.Ctx) error {
    id := c.Params("id")
    
    // Vulnerable: no ownership check
    resource := ResourceStore.Get(id)
    return c.JSON(resource)
})

With sequential or guessable IDs, attackers enumerate through the ID space to access resources belonging to other users or tenants.

Detecting Zone Transfer vulnerabilities in Fiber applications requires both static analysis and dynamic testing. Static analysis involves reviewing route handlers for authorization gaps:

func checkAuthorization(c *fiber.Ctx, resourceID string) error {
    // Verify resource belongs to current tenant/user
    tenantID := c.Locals("tenantID").(string)
    ownerID := getResourceOwner(resourceID)
    
    if ownerID != tenantID {
        return fiber.ErrForbidden
    }
    return nil
}

// Test endpoint with authorization check
app.GET("/api/resources/:id", func(c *fiber.Ctx) error {
    id := c.Params("id")
    
    if err := checkAuthorization(c, id); err != nil {
        return err
    }
    
    resource := ResourceStore.Get(id)
    return c.JSON(resource)
})

Dynamic testing with middleBrick specifically targets these vulnerabilities by scanning endpoints without credentials and attempting resource enumeration. middleBrick's black-box scanning methodology tests the unauthenticated attack surface by systematically probing endpoints with different parameters to detect zone transfer patterns.

For Fiber applications, middleBrick analyzes the runtime behavior of endpoints, looking for:

• Predictable resource identifiers that can be enumerated
• Endpoints that return collections without proper tenant scoping
• Missing authorization checks in CRUD operations
• GraphQL resolvers that don't validate field-level permissions

middleBrick's scanning process for Zone Transfer specifically includes testing common enumeration patterns like /api/resources/1, /api/resources/2 and analyzing response differences that might indicate successful data access across zones.

Additionally, middleBrick can analyze OpenAPI specifications alongside runtime scanning. For Fiber applications using automatic OpenAPI generation, middleBrick cross-references documented endpoints with actual behavior, identifying discrepancies where documentation suggests proper authorization but runtime scanning reveals vulnerabilities.

Remediating Zone Transfer vulnerabilities in Fiber requires implementing proper authorization at both the application and database levels. The most effective approach combines middleware-based authorization with database query scoping.

First, implement tenant-aware middleware that validates and scopes all requests:

func TenantMiddleware(allowedTenants []string) fiber.Handler {
    return func(c *fiber.Ctx) error {
        tenantID := c.Get("X-Tenant-ID")
        
        if !contains(allowedTenants, tenantID) {
            return fiber.ErrForbidden
        }
        
        // Scope database queries to tenant
        c.Locals("tenantID", tenantID)
        return c.Next()
    }
}

// Apply middleware to tenant routes
app.Use("/api/tenants/:tenantID", TenantMiddleware(allTenantIDs))

// Resource endpoint with proper scoping
app.GET("/api/tenants/:tenantID/resources", func(c *fiber.Ctx) error {
    tenantID := c.Params("tenantID")
    
    // Database query scoped to tenant
    resources := db.Query("SELECT * FROM resources WHERE tenant_id = ?", tenantID)
    return c.JSON(resources)
})

For individual resource access, implement ownership verification:

func ResourceOwnershipMiddleware() fiber.Handler {
    return func(c *fiber.Ctx) error {
        resourceID := c.Params("id")
        tenantID := c.Locals("tenantID").(string)
        
        // Verify resource belongs to tenant
        owner := getResourceOwner(resourceID)
        if owner != tenantID {
            return fiber.ErrForbidden
        }
        
        return c.Next()
    }
}

// Apply ownership check to resource routes
app.Use("/api/resources/:id", ResourceOwnershipMiddleware())

app.GET("/api/resources/:id", func(c *fiber.Ctx) error {
    id := c.Params("id")
    resource := ResourceStore.Get(id)
    return c.JSON(resource)
})

For GraphQL APIs built with Fiber, implement field-level authorization:

type resolver struct{}

func (r *resolver) Resources(ctx context.Context, tenantID string) ([]*Resource, error) {
    // Verify caller has access to requested tenant
    currentTenant := auth.GetTenantFromContext(ctx)
    if currentTenant != tenantID {
        return nil, errors.New("forbidden")
    }
    
    return db.ResourcesByTenant(tenantID)
}

func (r *resolver) Resource(ctx context.Context, id string) (*Resource, error) {
    // Verify ownership
    resource, err := db.ResourceByID(id)
    if err != nil {
        return nil, err
    }
    
    currentTenant := auth.GetTenantFromContext(ctx)
    if resource.TenantID != currentTenant {
        return nil, errors.New("forbidden")
    }
    
    return resource, nil
}

middleBrick's continuous monitoring in Pro tier helps verify these remediations by regularly scanning your APIs and alerting if zone transfer vulnerabilities reappear after code changes or deployments.