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Lack of data validation - HTML code


Implementation of proper data validation for HTML code


  • Usage of Node.js v14.15.4 as the runtime environment for executing JavaScript code
  • Usage of Express for building web applications and APIs


Non compliant code

import express from 'express';

const app = express();'/api/data', (req, res) => {
const { htmlCode } = req.body;


app.listen(3000, () => {
console.log('Server is running on port 3000');

The vulnerability in this code is a lack of data validation for the htmlCode field that is received in the request body. This field is directly used to construct an HTML response without any validation or sanitization.

This means that an attacker can inject arbitrary HTML code into the htmlCode field, which will be rendered as part of the response. This can lead to various security issues, including:

  1. Cross-Site Scripting (XSS): An attacker can inject malicious scripts that will be executed by the victim's browser, allowing them to steal sensitive information, perform actions on behalf of the user, or modify the content of the page.

  2. Log File Injection: An attacker can inject special characters that can manipulate log files, potentially leading to unauthorized access or information disclosure.

  3. Remote Command Execution: By injecting specific commands, an attacker can execute arbitrary code on the server, leading to complete compromise of the system.

  4. Insecure File Fetching: An attacker can inject URLs to fetch arbitrary files from external sources, potentially leading to the execution of malicious content or unauthorized access to sensitive files.

Additionally, the vulnerability allows an attacker to create delivery requests for non-existent QR codes. This is because the code does not validate the idQR field, which accepts text strings with random characters. This can lead to unnecessary processing and resource consumption.

To mitigate this vulnerability, it is recommended to implement server-side data validation and sanitization. This can include:

  1. Validating the data type and format of the htmlCode field to ensure it contains only safe and expected content.

  2. Sanitizing the htmlCode field to remove any potentially malicious HTML tags or scripts.

  3. Implementing proper input validation and filtering for the idQR field to only accept valid input and prevent unnecessary processing.

By implementing these measures, the code can prevent the injection of malicious HTML code and ensure the security and integrity of the application.


  • Implement server-side data validation for the 'htmlCode' field in the '/api/data' route.
  • Use a library or built-in functions to sanitize and validate the HTML code before rendering it.
  • Consider using a content security policy (CSP) to further mitigate the risk of code injection.
  • Regularly update and patch the dependencies used in the application to ensure the latest security fixes.
  • Perform security testing and code reviews to identify and fix any other potential vulnerabilities.

Compliant code

import express from 'express';
import { sanitize } from 'sanitize-html';

const app = express();

app.use(express.json());'/api/data', (req, res) => {
const { htmlCode } = req.body;

// Sanitize the HTML code
const sanitizedHtmlCode = sanitize(htmlCode);


app.listen(3000, () => {
console.log('Server is running on port 3000');

The fixed code addresses the vulnerability by implementing data validation on the server side. Here's how the code works:

  1. The code imports the necessary modules, including the express framework and the sanitize-html library for sanitizing HTML code.

  2. An instance of the Express application is created using express().

  3. The application is configured to parse JSON data using express.json() middleware.

  4. A POST route is defined at /api/data to handle incoming requests.

  5. Inside the route handler, the HTML code is extracted from the request body using destructuring assignment and stored in the htmlCode variable.

  6. The sanitize function from the sanitize-html library is used to sanitize the HTML code. This function removes any potentially dangerous elements or attributes from the code.

  7. The sanitized HTML code is then wrapped in a &lt;div> element and sent as the response using the res.send() method.

  8. The server is started and listens on port 3000.

By using the sanitize-html library to sanitize the HTML code, the fixed code ensures that any potentially malicious code is removed before it is rendered on the site. This prevents the injection of valid HTML code that could be interpreted by the receiving site.