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CSV injection

Need​

Prevention of CSV injection attacks

Context​

  • Usage of Go 1.16 for developing high-performance and concurrent applications
  • Usage of gin-gonic/gin for building web applications in Go
  • Usage of encoding/csv for reading and writing CSV files
  • Usage of the os module for interacting with the operating system in Node.js

Description​

Non compliant code​

package main

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

func main() {
	r := gin.Default()
	r.GET("/export", func(c *gin.Context) {
		file, err := os.Create("result.csv")
		if err != nil {
			c.JSON(500, gin.H{"message": "Unable to create CSV file"})
			return
		}
		writer := csv.NewWriter(file)
		defer writer.Flush()

		data := []string{"Name", "Email", "=1+1", "Address"}
		err = writer.Write(data)
		if err != nil {
			c.JSON(500, gin.H{"message": "Unable to write to CSV file"})
			return
		}

		c.JSON(200, gin.H{"message": "CSV file created successfully"})
	})
	r.Run()
}

The above code represents a Gin framework-based Go backend application that exports data as a CSV file. The code uses the csv package from the Go standard library to create and write to a CSV file.

The vulnerability lies in the data that is written to the CSV file. The data array contains a string =1+1. This string is a formula that can be interpreted by Excel. When the CSV file is opened in Excel, the formula will be executed, and the cell will display the result of the formula, which is 2.

This is a CSV Injection vulnerability, as an attacker could inject malicious formulas to perform harmful actions. For example, an attacker could inject a formula that calls a remote service, potentially leaking sensitive data.

The CSV Injection vulnerability is particularly dangerous because the malicious code will be executed as soon as the CSV file is opened in Excel, without any user interaction. This makes it a very effective attack vector for attackers.

Steps​

  • Sanitize user input: Before writing any data to the CSV file, ensure that user input is properly sanitized to prevent any malicious formulas or code injection.
  • Validate input data: Validate the input data to ensure that it meets the expected format and does not contain any unexpected characters or patterns.
  • Escape special characters: When writing data to the CSV file, escape any special characters that could be interpreted as formulas by Excel. This can be done by enclosing the data in double quotes or using a CSV library that automatically handles escaping.
  • Use a secure CSV library: Instead of using the standard encoding/csv package, consider using a more secure CSV library that provides additional protection against CSV injection vulnerabilities.
  • Educate users: Inform users about the potential risks of opening CSV files in Excel and advise them to use alternative software or take precautions when opening CSV files.
  • Regularly update dependencies: Keep all dependencies, including the gin framework, up to date to ensure that any security patches or fixes are applied.

Compliant code​

package main

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

func main() {
	r := gin.Default()
	r.GET("/export", func(c *gin.Context) {
		file, err := os.Create("result.csv")
		if err != nil {
			c.JSON(500, gin.H{"message": "Unable to create CSV file"})
			return
		}
		writer := csv.NewWriter(file)
		defer writer.Flush()

		data := []string{"Name", "Email", "=1+1", "Address"}
		for i, item := range data {
			if strings.HasPrefix(item, "=") || strings.HasPrefix(item, "+") || strings.HasPrefix(item, "-") || strings.HasPrefix(item, "@") {
				data[i] = "'" + item
			}
		}
		err = writer.Write(data)
		if err != nil {
			c.JSON(500, gin.H{"message": "Unable to write to CSV file"})
			return
		}

		c.JSON(200, gin.H{"message": "CSV file created successfully"})
	})
	r.Run()
}

The updated code includes a fix for the CSV Injection vulnerability. The fix involves sanitizing the data before writing it to the CSV file. This is done by checking if any string in the data starts with characters that could be interpreted as formulas by Excel (i.e., "=", "+", "-", "@"). If a string starts with any of these characters, a single quote is prepended to the string. This effectively neutralizes the potential formula and prevents Excel from interpreting it as such.

This solution is a simple and effective way to prevent CSV Injection attacks. However, it's important to note that it only covers the most common cases. For a more comprehensive solution, consider using a secure CSV library that provides additional protection against CSV Injection vulnerabilities.

Also, remember to keep all dependencies, including the gin framework, up to date to ensure that any security patches or fixes are applied. And finally, educate users about the potential risks of opening CSV files in Excel and advise them to use alternative software or take precautions when opening CSV files.

References​

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