Cors Wildcard in Echo Go

Cors wildcard vulnerabilities in Echo Go applications typically occur when developers configure overly permissive Cross-Origin Resource Sharing (CORS) policies using wildcard origins. This manifests when Echo Go's middleware is set to allow all origins with a configuration like:

import "github.com/labstack/echo/v4/middleware"

func main() {
    e := echo.New()
    
    // VULNERABLE: Allows any origin
    e.Use(middleware.CORSWithConfig(middleware.CORSConfig{
        AllowOrigins: []string{"*"},
        AllowMethods: []string{http.MethodGet, http.MethodHead, http.MethodPut, http.MethodPatch, http.MethodPost, http.MethodDelete},
        AllowHeaders: []string{echo.HeaderOrigin, echo.HeaderContentType, echo.HeaderAccept},
    }))
    
    e.Start(":1323")
}

This configuration allows any website to make cross-origin requests to your Echo Go API, potentially exposing sensitive data. The vulnerability becomes particularly dangerous when combined with Echo Go's authentication middleware or when the API returns user-specific data without proper authorization checks.

In Echo Go, this issue often manifests through the CORS middleware's handling of preflight requests. When a browser sends an OPTIONS request to check CORS permissions, Echo Go's default behavior with wildcard configurations returns headers like:

Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS
Access-Control-Allow-Headers: Content-Type, Authorization

These headers tell the browser that any website can interact with your API, potentially bypassing same-origin policies that would normally protect user data.

Detecting CORS wildcard vulnerabilities in Echo Go applications requires examining both the middleware configuration and runtime behavior. Start by reviewing your Echo Go application's initialization code for wildcard patterns in CORS configuration.

Using middleBrick's CLI tool, you can scan Echo Go APIs for CORS misconfigurations:

npx middlebrick scan https://your-echo-api.com

The scan will specifically test for wildcard CORS policies and report findings with severity levels. middleBrick's detection includes:

• Analysis of Access-Control-Allow-Origin headers for wildcard (*) values
• Testing preflight OPTIONS requests to verify CORS policy enforcement
• Checking for missing or overly permissive CORS configurations
• Verifying that CORS policies don't conflict with authentication mechanisms

For manual testing in Echo Go applications, you can use curl to examine CORS headers:

curl -X OPTIONS https://your-echo-api.com/api/resource \
  -H "Origin: https://evil-site.com" \
  -H "Access-Control-Request-Method: POST" \
  -H "Access-Control-Request-Headers: Content-Type"

If the response includes "Access-Control-Allow-Origin: *", your Echo Go application has a CORS wildcard vulnerability. Additionally, check if the API responds to unauthorized requests with sensitive data when proper CORS restrictions aren't in place.

Remediating CORS wildcard vulnerabilities in Echo Go requires implementing proper origin validation and using Echo Go's middleware configuration options effectively. The most secure approach is to specify exact allowed origins rather than using wildcards:

import "github.com/labstack/echo/v4/middleware"

func main() {
    e := echo.New()
    
    // SECURE: Specify exact allowed origins
    e.Use(middleware.CORSWithConfig(middleware.CORSConfig{
        AllowOrigins: []string{
            "https://yourdomain.com",
            "https://yourotherdomain.com",
        },
        AllowMethods: []string{http.MethodGet, http.MethodHead, http.MethodPut, http.MethodPatch, http.MethodPost, http.MethodDelete},
        AllowHeaders: []string{echo.HeaderOrigin, echo.HeaderContentType, echo.HeaderAccept},
        AllowCredentials: true, // If using cookies/session auth
    }))
    
    e.Start(":1323")
}

For Echo Go applications that need dynamic origin validation, you can implement a custom CORS middleware that validates origins against a whitelist:

import "github.com/labstack/echo/v4/middleware"

func customCORS(next echo.HandlerFunc) echo.HandlerFunc {
    allowedOrigins := map[string]bool{
        "https://yourdomain.com": true,
        "https://yourotherdomain.com": true,
    }
    
    return func(c echo.Context) error {
        origin := c.Request().Header.Get("Origin")
        if origin == "" || allowedOrigins[origin] {
            c.Response().Header().Set("Access-Control-Allow-Origin", origin)
            c.Response().Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
            c.Response().Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
            c.Response().Header().Set("Access-Control-Allow-Credentials", "true")
            
            if c.Request().Method == "OPTIONS" {
                return c.NoContent(204)
            }
        }
        return next(c)
    }
}

func main() {
    e := echo.New()
    e.Use(customCORS)
    e.Start(":1323")
}

When using Echo Go with authentication, ensure CORS policies don't inadvertently expose authenticated endpoints. Consider implementing additional security layers such as rate limiting and request validation to complement your CORS configuration.