Lack of data validation - Responses

Need

Implementation of robust data validation for response data

Context

• Usage of Go 1.16 for building efficient and scalable applications
• Usage of Gin framework for building web applications in Go

Description

Non compliant code

package main

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

type User struct {
	ID   string `json:"id"`
	Name string `json:"name"`
}

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

	r.GET("/user/:id", func(c *gin.Context) {
		userID := c.Param("id")
		// assume we get the user data from database
		user := User{ID: userID, Name: "John Doe"}
		c.JSON(200, gin.H{
			"user": user,
		})
	})

	r.POST("/updateUser", func(c *gin.Context) {
		var user User
		if err := c.ShouldBindJSON(&user); err != nil {
			c.JSON(400, gin.H{"error": err.Error()})
			return
		}
		// assume we update the user data in database
		c.JSON(200, gin.H{
			"message": "User updated successfully",
		})
	})

	r.Run()
}

The above Go code represents a simple backend application using the Gin framework. It has two endpoints. The first endpoint /user/:id is a GET method that retrieves the user's information based on the user id passed in the URL. The second endpoint /updateUser is a POST method that updates the user's information based on the JSON data sent in the request body.

The vulnerability here lies in the /updateUser endpoint. The endpoint takes the user's information from the request without validating the data. This means that if a response from the /user/:id endpoint is manipulated and sent as a request to the /updateUser endpoint, the application will accept the manipulated data without any validation.

For example, if a malicious actor changes the user's ID in the response from the /user/:id endpoint to an invalid ID and sends it as a request to the /updateUser endpoint, the application will update the user's information with the invalid ID without any validation. This can lead to various issues such as data inconsistency or even data corruption.

Steps

• Implement data validation on the server-side to ensure the integrity and validity of the received data.
• Validate the data received in the POST /updateUser endpoint before updating the user data in the database.
• Use appropriate validation techniques such as input sanitization, data type validation, length validation, and format validation.
• Handle validation errors properly and return meaningful error messages to the client.
• Consider using a validation library or framework to simplify the validation process.
• Avoid relying solely on client-side validation as it can be bypassed.
• Regularly review and update the validation logic to adapt to changing requirements and potential new vulnerabilities.

Compliant code

package main

import (
	"github.com/gin-gonic/gin"
	"github.com/go-playground/validator/v10"
)

type User struct {
	ID   string `json:"id" validate:"required,uuid"`
	Name string `json:"name" validate:"required"`
}

var validate *validator.Validate

func main() {
	r := gin.Default()
	validate = validator.New()

	r.GET("/user/:id", func(c *gin.Context) {
		userID := c.Param("id")
		// assume we get the user data from database
		user := User{ID: userID, Name: "John Doe"}
		c.JSON(200, gin.H{
			"user": user,
		})
	})

	r.POST("/updateUser", func(c *gin.Context) {
		var user User
		if err := c.ShouldBindJSON(&user); err != nil {
			c.JSON(400, gin.H{"error": err.Error()})
			return
		}

		// Validate the data
		err := validate.Struct(user)
		if err != nil {
			c.JSON(400, gin.H{"error": err.Error()})
			return
		}

		// assume we update the user data in database
		c.JSON(200, gin.H{
			"message": "User updated successfully",
		})
	})

	r.Run()
}

The updated code now includes data validation for the User struct using the validator package. The User struct now includes validate tags that specify the validation rules for each field. The ID field is required and must be a valid UUID, and the Name field is required.

In the main function, a new validator.Validate instance is created and assigned to the global validate variable. This instance is used to validate the User data in the POST /updateUser endpoint.

In the POST /updateUser endpoint, after binding the JSON request body to the User struct, the User data is validated using the validate.Struct method. If the validation fails, an error message is returned to the client with a 400 status code, and the function returns immediately. If the validation succeeds, the user data is updated in the database.

This update ensures that only valid User data is accepted and processed by the server, preventing potential issues caused by invalid data.

References

• 191.Lack of data validation - Responses