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Insecure functionality - File Creation

Need​

Enhancement of secure functionality - File Creation restriction enforcement

Context​

  • Usage of Go 1.16 for building high-performance and scalable applications
  • Usage of gin-gonic/gin for building web applications and APIs in Go
  • Usage of the os module for accessing operating system-related information

Description​

Non compliant code​

// Vulnerable code
package main

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

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

	r.POST("/create", func(c *gin.Context) {
		fileName := c.PostForm("fileName")
		_, err := os.Create(fileName)
		if err != nil {
			c.JSON(500, gin.H{
				"message": "Error creating file",
			})
			return
		}

		c.JSON(200, gin.H{
			"message": "File created",
		})
	})

	r.Run()
}

This code represents a vulnerability related to insecure functionality - file creation. In this code, we have a POST endpoint /create which takes a fileName from the request body and creates a file with that name.

The vulnerability lies in the fact that there are no checks to verify if the authenticated user has the necessary permissions to create a file. The restriction of this functionality is performed on the front end by disabling the corresponding button. However, this can be easily bypassed by an attacker who can send a POST request directly to the /create endpoint, thereby bypassing the front-end checks.

This can lead to serious security implications as an attacker can potentially create files with any name, which can lead to overwriting of existing files, creation of malicious files, or even exhausting the server's storage.

Therefore, it is essential to implement server-side checks to verify the user's permissions before processing the file creation request.

Steps​

  • Implement proper authorization and authentication mechanisms to ensure that only authorized users can access the functionality.
  • Validate and sanitize user input to prevent any malicious input from being processed.
  • Use a whitelist approach to restrict the allowed file names that can be created.
  • Implement server-side file name validation to ensure that the file name meets the required criteria.
  • Consider using a secure file storage mechanism instead of creating files directly on the server's file system.
  • Log and monitor any file creation activities to detect and respond to any suspicious or unauthorized file creation attempts.

Compliant code​

package main

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

var allowedFiles = map[string]bool{
	"file1.txt": true,
	"file2.txt": true,
	// Add more allowed files here
}

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

	r.Use(AuthMiddleware())

	r.POST("/create", func(c *gin.Context) {
		fileName := c.PostForm("fileName")

		// Validate file name
		if !allowedFiles[fileName] {
			c.JSON(403, gin.H{
				"message": "Unauthorized file creation attempt",
			})
			return
		}

		_, err := os.Create(fileName)
		if err != nil {
			c.JSON(500, gin.H{
				"message": "Error creating file",
			})
			return
		}

		c.JSON(200, gin.H{
			"message": "File created",
		})
	})

	r.Run()
}

func AuthMiddleware() gin.HandlerFunc {
	return func(c *gin.Context) {
		// Implement your authentication logic here
		// If authentication fails, return a 401 status code and stop the request processing
		// If authentication succeeds, proceed with the request processing
	}
}

The updated code includes an authentication middleware that is used to authenticate all incoming requests. This middleware should be implemented with the appropriate authentication logic to ensure that only authenticated users can access the file creation functionality.

The POST handler for the "/create" route now includes a validation step that checks if the requested file name is included in a whitelist of allowed file names. If the file name is not in the whitelist, the server responds with a 403 status code and an error message, and the request processing is stopped.

If the file name is in the whitelist, the server proceeds to create the file. If there is an error during file creation, the server responds with a 500 status code and an error message. If the file is created successfully, the server responds with a 200 status code and a success message.

This updated code ensures that only authenticated users can create files, and only files with names in the whitelist can be created. This prevents unauthorized file creation and restricts the allowed file names, addressing the identified vulnerability.

References​

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