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Lack of data validation - HTML code

Need​

Implementation of robust data validation for HTML code

Context​

  • Usage of Go 1.16 for building efficient and scalable applications
  • Usage of Gin framework 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("/data", func(c *gin.Context) {
		data := c.Query("data")
		c.JSON(200, gin.H{
			"message": data,
		})
	})

	r.Run()
}

In the above code snippet, we have a simple server set up using the Gin framework in Go. This server has a single endpoint /data that accepts a GET request with a query parameter data.

The vulnerability lies in the function handling GET requests to this endpoint. The handler function directly takes the data query parameter from the request and sends it back in the response as a JSON object without any form of validation or sanitization. This means that if a client sends a request with HTML code as the data query parameter, this HTML code will be included in the JSON response.

This lack of data validation poses a serious security risk. An attacker could inject malicious HTML code as the data query parameter, which would then be returned in the server's response. If this response is interpreted by a website and the HTML code is rendered, it could lead to various types of attacks such as Cross-Site Scripting (XSS).

For example, an attacker could send a request like /data?data=<script>malicious_code_here</script>. The server would then return this script in the JSON response, and if this response is used in a context where the HTML code is rendered, the malicious script could be executed.

Steps​

  • Implement input validation to sanitize the 'data' parameter received in the request.
  • Use a library or built-in functions to escape or sanitize any HTML code in the 'data' parameter.
  • Ensure that the 'data' parameter is properly validated and sanitized before using it in the response.
  • Consider using a Content Security Policy (CSP) to restrict the execution of any injected scripts or styles.
  • Regularly update and patch the dependencies used in the application to prevent known vulnerabilities.

Compliant code​

package main

import (
	"github.com/gin-gonic/gin"
	"net/http"
	"html"
)

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

	r.GET("/data", func(c *gin.Context) {
		data := c.Query("data")
		// Sanitize the data input
		safeData := html.EscapeString(data)
		c.JSON(http.StatusOK, gin.H{
			"message": safeData,
		})
	})

	r.Run()
}

The original code was vulnerable to HTML injection because it did not sanitize the 'data' parameter received in the request. This could allow an attacker to inject malicious HTML code, which could then be interpreted and executed by the browser.

The fixed code mitigates this vulnerability by using the html.EscapeString function from Go's built-in html package to sanitize the 'data' parameter. This function replaces special HTML characters like &lt;, >, &, ', and " with their respective HTML entities, effectively preventing any injected HTML code from being interpreted as actual HTML.

In addition to this, it's also recommended to implement a Content Security Policy (CSP) to further restrict the execution of any injected scripts or styles. Regularly updating and patching the dependencies used in the application can also help prevent known vulnerabilities.

References​

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