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Authentication mechanism absence or evasion - Redirect

Need​

Implementation of a robust and secure authentication mechanism

Context​

  • Usage of Go 1.15 for developing high-performance and scalable applications
  • Usage of gin-gonic/gin for building web applications in Go

Description​

Non compliant code​

package main

import (
	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()

	r.GET("/profile", func(c *gin.Context) {
		username := c.Query("username")
		if username != "" {
			c.Redirect(302, "/profile/"+username)
		} else {
			c.String(200, "Invalid request")
		}
	})
	r.Run()
}

This code is a simple Go application using the Gin framework. It defines a single route, /profile, which takes a username query parameter and redirects the client to a new URL based on that username.

The vulnerability here lies in the lack of authentication mechanism. There is no check to verify if the provided username belongs to an authenticated user. An attacker can bypass the authentication by simply knowing a valid username and manipulating the username query parameter in the /profile route.

For example, an attacker can send a GET request to /profile?username=admin and the server will respond with a redirect to /profile/admin, potentially exposing sensitive information about the 'admin' user. This is a clear example of an Authentication Mechanism Absence or Evasion vulnerability, where the attacker is able to bypass or evade the application's authentication mechanism.

Steps​

  • Implement a proper authentication mechanism to verify the user's identity before granting access to sensitive resources.
  • Use a secure session management technique to maintain the user's session state.
  • Ensure that the redirect URL is validated and authorized before redirecting the user.
  • Implement proper input validation and sanitization to prevent any malicious input from being processed.
  • Consider using a secure framework or library that provides built-in authentication and authorization features.
  • Regularly update and patch the application and its dependencies to address any security vulnerabilities.

Compliant code​

package main

import (
	"github.com/gin-gonic/gin"
	"github.com/gin-contrib/sessions"
	"github.com/gin-contrib/sessions/cookie"
)

func main() {
	r := gin.Default()

	store := cookie.NewStore([]byte("secret"))
	r.Use(sessions.Sessions("mysession", store))

	r.GET("/login", func(c *gin.Context) {
		session := sessions.Default(c)
		session.Set("user", "username")
		session.Save()
		c.String(200, "Logged in")
	})

	r.GET("/profile", func(c *gin.Context) {
		session := sessions.Default(c)
		username := session.Get("user")
		if username != nil {
			c.Redirect(302, "/profile/"+username.(string))
		} else {
			c.String(200, "Invalid request")
		}
	})
	r.Run()
}

The updated code now includes a proper authentication mechanism using sessions. The github.com/gin-contrib/sessions package is used to manage sessions in the application. A new session store is created using a secret key and the Sessions middleware is added to the Gin engine.

A new /login route is added where a user can log in. In a real-world application, you would validate the user's credentials before logging them in. For simplicity, this example just sets a static username in the session.

In the /profile route, the username is now retrieved from the session instead of the query string. If the username is not found in the session (i.e., the user is not logged in), the request is considered invalid. This prevents an attacker from gaining access to the application by knowing a valid username and changing the redirect.

This code also ensures that the redirect URL is validated and authorized before redirecting the user. The redirect URL is now based on the username stored in the session, which is set after the user logs in.

Remember to always validate and sanitize any user input in your application to prevent any malicious input from being processed. Also, consider using a secure framework or library that provides built-in authentication and authorization features. Regularly update and patch your application and its dependencies to address any security vulnerabilities.

References​

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