CWE-85: Doubled Character XSS Manipulations

What is Doubled Character XSS Manipulations?

• Overview: Doubled Character XSS Manipulations (CWE-85) occurs when a web application fails to filter user input for scripts disguised by doubling characters, allowing attackers to execute scripts through seemingly benign input.

• Exploitation Methods:

• Attackers can exploit this vulnerability by inserting scripts with doubled characters, tricking the application into processing the input without proper sanitization.
• Common attack patterns include duplicating characters in script tags or JavaScript commands to bypass basic input validation and filtering mechanisms.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized script execution in the context of the user's session, leading to data theft or session hijacking.
• Potential cascading effects involve spreading malware or phishing attacks, as well as further exploitation of other vulnerabilities.
• Business impact may include loss of user trust, damage to brand reputation, legal liabilities, and financial losses due to data breaches.

• Prevention Guidelines:

• Specific code-level fixes include implementing robust input validation and output encoding to prevent any script execution, particularly focusing on detecting and removing doubled characters.
• Security best practices involve employing a Content Security Policy (CSP) and consistently updating and patching web applications to address known vulnerabilities.
• Recommended tools and frameworks include using established libraries and frameworks like OWASP's AntiSamy or Microsoft’s AntiXSS Library that provide built-in protection against XSS attacks, including doubled character manipulations.

Corgea can automatically detect and fix Doubled Character XSS Manipulations in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Certainly! Below is the improved content for the code examples demonstrating CWE-85 (Doubled Character XSS Manipulations):

JavaScript Example

// Vulnerable code demonstrating CWE-85: Doubled Character XSS Manipulations
const express = require('express');
const app = express();

app.get('/search', (req, res) => {
    // Assume the input is expected to be some text query
    const query = req.query.q || '';

    // Vulnerability: unsanitized and unchecked input is directly inserted into HTML
    // An attacker can use doubled characters to bypass naive filtering and execute scripts
    res.send(`<div>Search results for: \${query}</div>`);
});

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

Explanation:

• Vulnerable Code: The input from the user is directly inserted into the HTML response without any sanitization or validation. Attackers can exploit this by using techniques such as doubling characters to evade basic filters and inject malicious scripts.

How to fix Doubled Character XSS Manipulations?

To fix the vulnerability, it's crucial to properly sanitize and encode user input before embedding it in HTML content. The fix involves:

1. Sanitization and Encoding: Remove potentially harmful parts of the input and encode it to ensure it is safe for HTML rendering.
2. Use Libraries: Utilize libraries that handle XSS protection effectively, including known vectors like doubled character manipulations.

In JavaScript/Node.js, libraries such as xss or sanitize-html can be used for input sanitization and encoding.

Fixed Code Example

// Fixed code implementing input sanitization and encoding
const express = require('express');
const xss = require('xss'); // Importing xss library for sanitization
const app = express();

app.get('/search', (req, res) => {
    const query = req.query.q || '';

    // Fix: Use xss library to sanitize and encode input
    const safeQuery = xss(query);

    // Now, the input is sanitized, preventing XSS attacks
    res.send(`<div>Search results for: \${safeQuery}</div>`);
});

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

Explanation:

• Fixed Code: By using the xss library, we sanitize the user input. This library encodes potentially dangerous characters and removes harmful content, effectively mitigating XSS risks, including those exploiting doubled characters.

By implementing this fix, you ensure that any user input rendered in the HTML is safe, preventing it from being executed as a script, thus protecting against XSS attacks.