Sandbox Escape in Echo Go with Bearer Tokens

A sandbox escape in the context of an Echo Go API occurs when an attacker who has obtained a Bearer Token bypasses intended execution boundaries and accesses or modifies resources that should be isolated. Bearer Tokens are commonly used in Echo Go routes to authorize requests; if token validation is incomplete or misapplied, an attacker can leverage a single compromised token to traverse route-level restrictions.

Echo Go applications often define middleware that checks for a Bearer Token in the Authorization header and attaches user context to the request. A vulnerability arises when authorization checks are applied inconsistently across routes or when token validation does not enforce scope, audience, or role constraints. For example, an API might have an administrative route intended to be accessible only to users with elevated privileges, but if the middleware only verifies the presence of a valid Bearer Token without inspecting claims, an attacker can use a low-privilege token to invoke admin endpoints.

In a real-world scenario, an attacker might exploit improper route isolation to perform Broken Level of Authorization (BOLA). Consider an Echo Go service where a route like /users/{id}/profile is protected only by a Bearer Token check, while the token itself includes a user identifier. If the server does not compare the {id} path parameter with the user identifier embedded in the token claims, an attacker can modify the path parameter to access or update another user’s profile simply by presenting the same Bearer Token.

Another vector involves insecure direct object references (IDOR) enabled by lax token usage. If the API relies solely on Bearer Token validation without additional ownership checks, an attacker can iterate over resource identifiers while using the same token, effectively escaping the intended sandbox of access control. This is particularly dangerous when the token does not carry fine-grained permissions or when these permissions are not enforced at the handler level.

Echo Go APIs that integrate token-based authentication without complementary scope validation or route-specific authorization logic create conditions where a compromised Bearer Token can lead to broader access than intended. The combination of token-centric security and insufficient route or claim enforcement allows attackers to traverse access boundaries, exposing administrative operations or sensitive data endpoints that should remain isolated.

Remediation focuses on validating Bearer Tokens with strict claim checks and enforcing route-specific authorization in Echo Go handlers. Developers should verify not only the presence of a token but also its scope, audience, and roles before allowing access to sensitive endpoints.

Below is an example of secure Bearer Token validation in Echo Go. The middleware extracts the token, validates its signature, and checks required claims before proceeding.

// middleware/auth.go
package middleware

import (
	"context"
	"net/http"
	"strings"

	"github.com/golang-jwt/jwt/v5"
	"github.com/labstack/echo/v4"
)

type Claims struct {
	Scope  string `json:"scope"`
	Roles  []string `json:"roles"`
	UserID string `json:"sub"`
	jwt.RegisteredClaims
}

func BearerAuth(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		auth := c.Request().Header.Get("Authorization")
		if auth == "" {
			return echo.ErrUnauthorized
		}
		// Expecting "Bearer <token>"
		parts := strings.Split(auth, " ")
		if len(parts) != 2 || parts[0] != "Bearer" {
			return echo.ErrUnauthorized
		}
		tokenString := parts[1]
		claims := &Claims{}
		token, err := jwt.ParseWithClaims(tokenString, claims, func(token *jwt.Token) (interface{}, error) {
			// TODO: use a secure key retrieval method
			return []byte("your-secret-key"), nil
		})
		if err != nil || !token.Valid {
			return echo.ErrUnauthorized
		}
		// Attach claims to context for downstream handlers
		c.Set("userID", claims.UserID)
		c.Set("roles", claims.Roles)
		c.Set("scope", claims.Scope)
		return next(c)
	}
}

After validating the token, enforce role- or scope-based checks at the route level. For example, an admin route should explicitly verify that the token includes the required role.

// handlers/admin.go
package handlers

import (
	"net/http"

	"github.com/labstack/echo/v4"
)

func AdminHandler(c echo.Context) error {
	roles, ok := c.Get("roles").([]string)
	if !ok || !contains(roles, "admin") {
		return echo.ErrForbidden
	}
	return c.String(http.StatusOK, "Admin access granted")
}

func contains(slice []string, item string) bool {
	for _, s := range slice {
		if s == item {
			return true
		}
	}
	return false
}

For endpoints that involve resource-level access (e.g., /users/{id}/profile), ensure that the user ID in the path matches the user identifier in the token claims.

// handlers/user.go
package handlers

import (
	"net/http"
	"strconv"

	"github.com/labstack/echo/v4"
)

func GetUserProfile(c echo.Context) error {
	userID, err := strconv.Atoi(c.Param("id"))
	if err != nil {
		return echo.NewHTTPError(http.StatusBadRequest, "invalid user id")
	}
	claimsUserID, ok := c.Get("userID").(string)
	if !ok {
		return echo.ErrUnauthorized
	}
	// Ensure the requesting user matches the resource user
	if claimsUserID != strconv.Itoa(userID) {
		return echo.ErrForbidden
	}
	// Fetch and return profile for userID
	return c.JSON(http.StatusOK, map[string]string{"profile": "..."})
}

Additionally, scope validation should be applied for operations that require specific permissions beyond roles. When issuing tokens, include a scope claim and verify it in middleware.

// middleware/scope.go
package middleware

import (
	"net/http"

	"github.com/labstack/echo/v4"
)

func RequireScope(scope string) echo.MiddlewareFunc {
	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			scopes, ok := c.Get("scope").(string)
			if !ok || !hasScope(scopes, scope) {
				return echo.ErrForbidden
			}
			return next(c)
		}
	}
}

func hasScope(tokenScopes, required string) bool {
	for _, s := range splitScopes(tokenScopes) {
		if s == required {
			return true
		}
	}
	return false
}

func splitScopes(s string) []string {
	// simplistic split; adjust as needed
	return strings.Split(s, " ")
}

By combining robust Bearer Token validation with claim-based authorization and resource ownership checks, Echo Go APIs can prevent sandbox escapes and ensure that each token’s access remains confined to its intended boundaries.

• How can I test whether my Echo Go API is vulnerable to sandbox escape with Bearer Tokens?
  Use a scanner that supports unauthenticated attack surface testing, such as middleBrick, which runs 12 security checks in parallel including BOLA/IDOR and authentication validation to identify improper token usage and route isolation issues.

• Does using middleBrick reduce the need for manual code review of Bearer Token handling in Echo Go?
  middleBrick detects and reports findings with remediation guidance, but it does not fix, patch, block, or remediate. It provides structured output and prioritization to help developers focus manual review on high-risk areas like token validation and claim enforcement.