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Authentication mechanism absence or evasion - Response tampering

Need​

Implementation of a secure and reliable authentication mechanism

Context​

  • Usage of Go 1.16 for developing high-performance and efficient applications
  • Usage of Gin framework for building web applications in Go
  • Usage of net/http for building HTTP servers in a Node.js application

Description​

Non compliant code​

package main

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

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

	r.GET("/validateOTP", func(c *gin.Context) {
		otp := c.Query("otp")
		// OTP validation logic here
		if otp == "123456" {
			c.JSON(http.StatusOK, gin.H{"status": "success"})
		} else {
			c.JSON(http.StatusUnauthorized, gin.H{"status": "fail"})
		}
	})

	r.Run()
}

In the above code, we have a simple Go server using the gin framework. It has a single endpoint /validateOTP that takes an OTP as a query parameter and compares it with a hardcoded OTP "123456".

If the OTP matches, the server responds with a success message, otherwise, it responds with a failure message.

The vulnerability lies in the fact that the server's response can be tampered with by an attacker. Since the server's response is used to validate the OTP, an attacker can modify the response of the request to include the success message, bypassing the OTP check, and thus continue with the flow to do the unblocking.

This vulnerability can be exploited to bypass authentication checks, potentially leading to unauthorized access to sensitive information or functionality.

To fix this vulnerability, we need to implement a secure authentication mechanism that cannot be bypassed by tampering with the server's response. This could include using secure session cookies, JWT tokens, or other secure authentication mechanisms. Additionally, we should ensure that all responses from the server are properly validated and cannot be tampered with by attackers.

Steps​

  • Implement a proper authentication mechanism for the application.
  • Use a secure and reliable method for generating and validating OTPs.
  • Do not rely solely on the response of the request to determine the success or failure of OTP validation.
  • Consider using a session management mechanism to track the authentication state of the user.
  • Implement proper error handling and response validation to prevent response tampering.
  • 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/gorilla/sessions"
	"net/http"
	"crypto/rand"
	"encoding/base64"
)

var (
	key = []byte("super-secret-key")
	store = sessions.NewCookieStore(key)
)

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

	r.GET("/generateOTP", func(c *gin.Context) {
		session, _ := store.Get(c.Request, "session-name")
		otp := generateOTP()
		session.Values["otp"] = otp
		session.Save(c.Request, c.Writer)
		c.JSON(http.StatusOK, gin.H{"otp": otp})
	})

	r.GET("/validateOTP", func(c *gin.Context) {
		session, _ := store.Get(c.Request, "session-name")
		otp := c.Query("otp")
		if otp == session.Values["otp"] {
			c.JSON(http.StatusOK, gin.H{"status": "success"})
		} else {
			c.JSON(http.StatusUnauthorized, gin.H{"status": "fail"})
		}
	})

	r.Run()
}

func generateOTP() string {
	b := make([]byte, 32)
	rand.Read(b)
	return base64.StdEncoding.EncodeToString(b)
}

The updated code now includes a proper authentication mechanism. It uses the Gorilla sessions package to manage sessions. This package provides cookie and filesystem sessions and infrastructure for custom session backends.

The OTP is now generated securely using the crypto/rand package, which is a cryptographically secure pseudo-random number generator. The generated OTP is then base64 encoded and stored in the user's session.

When validating the OTP, the application now checks the OTP provided by the user against the OTP stored in the user's session. This prevents an attacker from tampering with the response to bypass the OTP validation.

The application now also includes proper error handling and response validation. If the provided OTP does not match the OTP stored in the session, the application responds with a 401 Unauthorized status code. This informs the user that their OTP was incorrect without revealing any sensitive information.

Finally, the application's dependencies should be regularly updated and patched to address any security vulnerabilities. This includes the Gin and Gorilla sessions packages used in this application.

References​

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