Skip to main content

Lack of data validation - Source Code

Need​

Implementation of robust data validation mechanisms in the source code

Context​

  • Usage of Go 1.16 for building scalable and efficient applications
  • Usage of Gin for building web applications in Go
  • Usage of RegExp for pattern matching and string manipulation

Description​

Non compliant code​

package main

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

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

	r.POST("/validate", func(c *gin.Context) {
		var json struct {
			Data string `json:"data" binding:"required"`
		}

		if c.Bind(&json) == nil {
			match, _ := regexp.MatchString("^[a-zA-Z0-9]*$", json.Data)
			if match {
				c.JSON(200, gin.H{
					"message": "Valid data",
				})
			} else {
				c.JSON(400, gin.H{
					"message": "Invalid data",
				})
			}
		}
	})

	r.Run()
}

In the code above, we are using the Gin framework to create a simple API endpoint that accepts POST requests at "/validate". The request should contain a JSON body with a "data" field. This "data" field is then matched against a regular expression to validate the input.

The vulnerability lies in the use of the regexp.MatchString function. This function uses a regular expression to check if the input string matches the pattern. The pattern ^[a-zA-Z0-9]*$ allows any alphanumeric characters. However, it is a dangerous regular expression because it can lead to ReDoS (Regular Expression Denial of Service) attacks. An attacker can send a specifically crafted string that would take a long time to evaluate, potentially causing the server to crash.

This vulnerability is due to the lack of proper data validation. The server blindly trusts the input without sanitizing or validating it properly. This can lead to various security issues, including the aforementioned ReDoS attacks.

Steps​

  • Replace the use of dangerous regular expressions with safer alternatives.
  • Use a whitelist approach to validate the input data.
  • Implement input validation using a well-tested library or framework.
  • Sanitize the input data to remove any potentially harmful characters or sequences.
  • Implement proper error handling to gracefully handle any unexpected input.

Compliant code​

package main

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

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

	r.POST("/validate", func(c *gin.Context) {
		var json struct {
			Data string `json:"data" binding:"required"`
		}

		if c.Bind(&json) == nil {
			// Use govalidator to validate the input data
			if govalidator.IsAlphanumeric(json.Data) {
				c.JSON(200, gin.H{
					"message": "Valid data",
				})
			} else {
				c.JSON(400, gin.H{
					"message": "Invalid data",
				})
			}
		}
	})

	r.Run()
}

The updated code replaces the use of dangerous regular expressions with a safer alternative. Instead of using regexp.MatchString, we are now using the govalidator.IsAlphanumeric function from the govalidator library to validate the input data. This function checks if the input string contains only alphanumeric characters (letters and numbers), which is a whitelist approach to input validation.

The govalidator library is a well-tested library for data validation in Go, and it provides a wide range of validation functions that can be used to validate different types of input data. By using this library, we can ensure that our input validation is robust and secure.

In addition, the updated code also implements proper error handling. If the input data is not valid, the server will respond with a 400 status code and a message indicating that the data is invalid. This allows the server to gracefully handle any unexpected input and prevents the server from crashing due to invalid input data.

References​

Last updated on