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Insecure temporary files

Need​

Secure handling of temporary files

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 io/ioutil for reading and writing files in Node.js

Description​

Non compliant code​

package main

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

func main() {
	r := gin.Default()
	r.GET("/sensitive", func(c *gin.Context) {
		// Writing sensitive information to a temporary file
		tempFile, _ := ioutil.TempFile("", "temp")
		tempFile.WriteString("Sensitive Information")
		tempFile.Close()

		// Reading sensitive information from the temporary file
		data, _ := ioutil.ReadFile(tempFile.Name())
		c.String(200, string(data))
	})
	r.Run()
}

In this code snippet, we are creating a temporary file and storing sensitive information in it. This is a security vulnerability because an attacker can potentially access this temporary file and retrieve the sensitive information.

The vulnerability lies in the following lines:

// Writing sensitive information to a temporary file
tempFile, _ := ioutil.TempFile("", "temp")
tempFile.WriteString("Sensitive Information")
tempFile.Close()

// Reading sensitive information from the temporary file
data, _ := ioutil.ReadFile(tempFile.Name())

Here, ioutil.TempFile is used to create a new temporary file in the default directory for temporary files with a name beginning with "temp". The second argument to ioutil.TempFile is the prefix for the generated temporary file name. Then, we write some sensitive information to this file with tempFile.WriteString and close the file.

Later, we read the sensitive information back from the temporary file with ioutil.ReadFile and serve it as a response to a GET request at the "/sensitive" route.

The problem with this approach is that the temporary file is not securely handled. It is created in a publicly accessible directory and contains sensitive information. This could allow an attacker who has access to the filesystem to read the contents of the temporary file and gain access to sensitive information.

Steps​

  • Avoid using temporary files to store sensitive information.
  • If sensitive information needs to be stored temporarily, consider using in-memory storage instead of writing to a file.
  • If temporary files are necessary, ensure that they are stored in a secure location with restricted access.
  • Implement proper file handling practices, such as setting appropriate file permissions and securely deleting temporary files after use.
  • Regularly review and audit the usage of temporary files in the application to identify any potential vulnerabilities.

Compliant code​

package main

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

var (
	memoryStore = make(map[string]string)
	mu          sync.RWMutex
)

func main() {
	r := gin.Default()
	r.GET("/sensitive", func(c *gin.Context) {
		// Writing sensitive information to in-memory storage
		mu.Lock()
		memoryStore["sensitive"] = "Sensitive Information"
		mu.Unlock()

		// Reading sensitive information from in-memory storage
		mu.RLock()
		data := memoryStore["sensitive"]
		mu.RUnlock()

		c.String(200, data)
	})
	r.Run()
}

The updated code avoids using temporary files to store sensitive information. Instead, it uses an in-memory storage solution. This is achieved by using a map in Go, which is a built-in data structure that can store key-value pairs.

The sync.RWMutex is used to ensure that the map is safe to use concurrently. This is important because the Gin framework handles each request in a separate goroutine, which can run concurrently with other goroutines.

The mu.Lock() and mu.Unlock() calls ensure that only one goroutine can write to the map at a time. This prevents race conditions, where two goroutines might try to update the same key in the map at the same time, leading to unpredictable results.

The mu.RLock() and mu.RUnlock() calls allow multiple goroutines to read from the map at the same time, as long as no other goroutine is writing to the map. This can improve performance by allowing multiple requests to be handled concurrently.

The sensitive information is stored in the map with the key "sensitive". When the "/sensitive" route is accessed, the server retrieves the sensitive information from the map and sends it in the response.

This solution is more secure than using temporary files, as it avoids the risk of the sensitive information being accessed by unauthorized users or processes that have access to the file system. It also avoids the risk of the sensitive information being left in a temporary file if the application crashes or is terminated unexpectedly.

References​

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