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Lack of data validation - Numbers

Need​

Implementation of robust data validation for numbers

Context​

  • Usage of Go 1.16 for building high-performance and scalable applications
  • Usage of gin-gonic/gin for building web applications in Go

Description​

Non compliant code​

package main

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

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

	r.GET("/api/data/:number", func(c *gin.Context) {
		number := c.Param("number")
		c.JSON(200, gin.H{
			"message": "Received number: " + number,
		})
	})

	r.Run()
}

The above code is a simple Go application using the Gin framework. It exposes an API endpoint at /api/data/:number that accepts a number as a URL parameter and returns a JSON response with a message that includes the received number.

The vulnerability lies in the fact that the code does not validate the number parameter. It directly takes the parameter from the URL and uses it in the response. This can lead to several issues:

  1. Type Issues: If a non-numeric value is passed, it can potentially break the business logic that assumes this value to be a number.

  2. Injection Attacks: Without validation, it's possible for an attacker to inject malicious data.

  3. Business Logic Violation: Depending on the business logic, certain numbers might not be allowed. For instance, negative numbers or numbers beyond a certain range might not be valid. Without proper validation, the application might end up processing invalid data.

In conclusion, lack of data validation for the number parameter can lead to unexpected behavior, potential security issues, and violation of business rules. It's crucial to validate all input data to ensure it conforms to the expected format and range.

Steps​

  • Implement data validation to ensure that the 'number' parameter is a valid number.
  • Use appropriate validation techniques such as regular expressions or built-in functions to check if the 'number' parameter is a valid number.
  • Handle invalid input by returning an appropriate error response to the client.
  • Consider using a validation library or framework to simplify the validation process.
  • Ensure that the validated 'number' parameter is used safely in the business logic to prevent any negative impact on the application.

Compliant code​

package main

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

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

	r.GET("/api/data/:number", func(c *gin.Context) {
		number := c.Param("number")

		// Validate that the number is a valid integer
		if _, err := strconv.Atoi(number); err != nil {
			c.JSON(400, gin.H{
				"error": "Invalid number format",
			})
			return
		}

		c.JSON(200, gin.H{
			"message": "Received number: " + number,
		})
	})

	r.Run()
}

The original code was vulnerable due to a lack of data validation. The 'number' parameter from the URL was directly used without checking if it was a valid number. This could lead to potential issues if the 'number' parameter was not a number, breaking the business logic of the application.

The fixed code now includes a validation step for the 'number' parameter. The strconv.Atoi function is used to try and convert the 'number' parameter to an integer. If this conversion fails (i.e., the 'number' parameter is not a valid number), an error is returned and the function returns a 400 status code with an error message to the client. This prevents the invalid 'number' parameter from being used in the rest of the business logic.

This fix ensures that only valid numbers are processed by the application, preventing potential issues caused by invalid input. It also provides a clear error message to the client when invalid input is provided, improving the usability of the API.

References​

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