CVE-2024-6783: Vue.js XSS via Prototype Pollution Flaw

CVE-2024-6783 Overview

A Cross-Site Scripting (XSS) vulnerability has been discovered in Vue.js that allows an attacker to execute arbitrary JavaScript code via prototype pollution. By manipulating the prototype chain of specific properties such as Object.prototype.staticClass or Object.prototype.staticStyle, attackers can inject and execute malicious JavaScript code in the context of the victim's browser session.

Critical Impact

Attackers can exploit this vulnerability to execute arbitrary JavaScript code in users' browsers, potentially leading to session hijacking, credential theft, defacement, or malware distribution through affected Vue.js applications.

Affected Products

• Vue.js framework (specific vulnerable versions not disclosed in advisory)

Discovery Timeline

• 2024-07-23 - CVE-2024-6783 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-6783

Vulnerability Analysis

This vulnerability combines two attack techniques: prototype pollution and Cross-Site Scripting (XSS). Prototype pollution is a JavaScript-specific vulnerability that occurs when an attacker can modify the prototype of a base object like Object.prototype. In Vue.js, certain rendering properties including staticClass and staticStyle are vulnerable to this manipulation.

When the Vue.js rendering engine processes components, it accesses these properties during the virtual DOM to real DOM conversion process. If an attacker has previously polluted Object.prototype.staticClass or Object.prototype.staticStyle with malicious payloads, the framework inadvertently incorporates these values into the rendered output, resulting in XSS execution.

The network-based attack vector requires the attacker to find a way to pollute the JavaScript prototype chain, typically through vulnerable JSON parsing, object merge operations, or other input handling mechanisms in the target application.

Root Cause

The root cause of this vulnerability lies in Vue.js's template rendering engine not properly isolating or sanitizing property lookups that traverse the prototype chain. When Vue accesses object properties like staticClass or staticStyle during component rendering, it does not verify whether these values originate from the object instance itself or have been inherited from a polluted prototype. This allows attacker-controlled values to flow into security-sensitive rendering contexts without proper sanitization, classified as CWE-79 (Improper Neutralization of Input During Web Page Generation).

Attack Vector

The attack requires the following conditions to be met:

1. The target application must have a prototype pollution vector that allows an attacker to set arbitrary properties on Object.prototype
2. The application must use Vue.js with vulnerable rendering paths that access staticClass or staticStyle properties
3. The attacker must craft a payload that, when assigned to these prototype properties, results in JavaScript execution when rendered

Once an attacker achieves prototype pollution (through mechanisms such as vulnerable _.merge() operations, insecure JSON parsing, or query parameter manipulation), they can set Object.prototype.staticClass or Object.prototype.staticStyle to contain XSS payloads. When Vue.js subsequently renders components, these polluted values are incorporated into the DOM, triggering script execution in the victim's browser context.

Detection Methods for CVE-2024-6783

Indicators of Compromise

• Unusual JavaScript objects containing staticClass or staticStyle properties with script content in application logs
• Client-side errors related to unexpected property types during Vue.js rendering
• Evidence of prototype pollution attempts in application input fields, URLs, or API requests
• Unexpected inline styles or class attributes appearing in rendered HTML output

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Deploy web application firewalls (WAF) with rules to detect prototype pollution payloads in request parameters
• Monitor client-side JavaScript errors for anomalies related to object property access during Vue.js rendering
• Use browser-based XSS auditing tools and integrate them into security testing pipelines

Monitoring Recommendations

• Enable verbose logging for Vue.js applications to capture rendering errors and warnings
• Implement real-time monitoring for CSP violation reports to detect potential XSS attempts
• Monitor application endpoints for suspicious input patterns commonly associated with prototype pollution attacks
• Set up alerts for unusual patterns in user-submitted data that contain JavaScript property manipulation syntax

How to Mitigate CVE-2024-6783

Immediate Actions Required

• Review and audit all locations in your application where user input is merged into JavaScript objects
• Implement Object.freeze() on critical objects to prevent prototype pollution
• Validate and sanitize all user inputs that could potentially reach object merge or assignment operations
• Consider implementing a strict Content Security Policy (CSP) to mitigate the impact of any successful XSS exploitation

Patch Information

Consult the official Vue.js security advisories and update to the latest patched version. Additional details are available through the GitHub Security Advisory GHSA-g3ch-rx76-35fx and the HeroDevs vulnerability directory.

Workarounds

• Implement prototype pollution prevention by freezing Object.prototype or using Object.create(null) for untrusted object operations
• Use libraries like lodash with secure configurations or dedicated sanitization libraries that prevent prototype pollution
• Deploy input validation that rejects payloads containing __proto__, constructor, or prototype strings
• Implement a strong Content Security Policy that blocks inline scripts and restricts script sources to trusted origins

# Example CSP header configuration to mitigate XSS impact
# Add to your web server configuration (nginx example)
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; object-src 'none';" always;

# For applications using helmet.js (Node.js/Express)
# In your application configuration:
# helmet.contentSecurityPolicy({
#   directives: {
#     defaultSrc: ["'self'"],
#     scriptSrc: ["'self'"],
#     objectSrc: ["'none'"]
#   }
# })