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Unauthorized access to files

Need​

Prevention of unauthorized access to files and functionalities

Context​

  • Usage of Go 1.15 for developing scalable and efficient applications
  • Usage of gin-gonic/gin for building web applications in Go
  • Usage of net/http for creating 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.PUT("/user/:name", func(c *gin.Context) {
		name := c.Param("name")
		userData := c.PostForm("data")

		// Vulnerable part: no validation or sanitization of user input
		err := updateUserData(name, userData)
		if err != nil {
			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
			return
		}

		c.JSON(http.StatusOK, gin.H{"status": "ok"})
	})

	r.Run() // listen and serve on 0.0.0.0:8080
}

func updateUserData(name string, data string) error {
	// Update user data in Sharepoint
	// This function is vulnerable as it directly uses user-provided data
	return nil
}

The vulnerability lies in the updateUserData function in the above code. This function takes two parameters: name and data. These parameters are directly obtained from the user input without any form of validation or sanitization, which makes the function susceptible to malicious input.

The name parameter is obtained from the URL parameter :name and the data parameter is obtained from the form data data. Both of these inputs are directly used in the updateUserData function without any checks or sanitization, which can lead to unauthorized access to files and functionalities.

A malicious user can inject potentially dangerous characters into these parameters that can lead to inappropriate behavior in the application. For instance, they can manipulate the data parameter to access and modify files in the Sharepoint without authorization.

To fix this vulnerability, the application should implement input validation and sanitization to ensure that the user-provided data does not contain any malicious characters or sequences. This can be done using regular expressions or by using a library that provides these functionalities. Moreover, the application should also implement proper access controls to ensure that a user can only access the files and functionalities that they are authorized to access.

Steps​

  • Implement input validation and sanitization to prevent injection of potentially dangerous characters.
  • Use a whitelist approach to validate and sanitize user input, allowing only specific characters or patterns.
  • Consider using regular expressions or predefined validation functions to ensure the input meets the expected format.
  • Escape or encode user input before using it in any sensitive context, such as accessing files or executing commands.
  • Implement proper access control mechanisms to restrict unauthorized access to functionalities and files.
  • Use authentication and authorization mechanisms to ensure that only authorized users can access sensitive functionalities and files.
  • Regularly update and patch the application and its dependencies to address any known security vulnerabilities.
  • Perform security testing, such as penetration testing, to identify and fix any other potential vulnerabilities in the application.

Compliant code​

package main

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

type UserInput struct {
	Name string `validate:"required,alpha"`
	Data string `validate:"required"`
}

var validate *validator.Validate

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

	r.PUT("/user/:name", func(c *gin.Context) {
		name := c.Param("name")
		userData := c.PostForm("data")

		input := &UserInput{
			Name: name,
			Data: userData,
		}

		err := validate.Struct(input)
		if err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}

		// Sanitize user input
		sanitizedData := sanitizeData(userData)

		err = updateUserData(name, sanitizedData)
		if err != nil {
			c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
			return
		}

		c.JSON(http.StatusOK, gin.H{"status": "ok"})
	})

	r.Run() // listen and serve on 0.0.0.0:8080
}

func sanitizeData(data string) string {
	// Use a simple regex to remove any non-alphanumeric characters
	reg, _ := regexp.Compile("[^a-zA-Z0-9]+")
	sanitizedData := reg.ReplaceAllString(data, "")
	return sanitizedData
}

func updateUserData(name string, data string) error {
	// Update user data in Sharepoint
	// This function is now safe as it uses sanitized user-provided data
	return nil
}

The updated code now includes input validation and sanitization to prevent injection of potentially dangerous characters.

The UserInput struct is used to define the expected format of the user input. The validate tags are used to specify the validation rules for each field. In this case, the Name field is required and must only contain alphabetic characters, and the Data field is required.

The validate.Struct(input) function is used to validate the user input against the defined struct. If the validation fails, an error is returned and the function exits.

The sanitizeData function is used to sanitize the user data. It uses a regular expression to remove any non-alphanumeric characters from the data. This is a simple example of sanitization, and more complex sanitization may be required depending on the specific requirements of your application.

The updateUserData function now uses the sanitized user data, which prevents injection of potentially dangerous characters.

In addition to these changes, it's important to implement proper access control mechanisms, use authentication and authorization mechanisms, regularly update and patch the application and its dependencies, and perform security testing to ensure the security of your application.

References​

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