CSS Injection Template

Executive Summary:

This report addresses a significant security vulnerability concerning CSS (Cascading Style Sheets) Injection within our application. CSS Injection occurs when untrusted input is improperly handled and executed within CSS code, leading to various security risks such as cross-site scripting (XSS), website defacement, or data manipulation. This report aims to detail the vulnerability, its potential impact, and recommendations for mitigation.

Description of the Vulnerability:

CSS Injection vulnerabilities arise when user-controllable input is incorporated directly into CSS code without proper validation or sanitization. Attackers can exploit these vulnerabilities by injecting malicious CSS code, such as JavaScript snippets, into input fields or URL parameters, which are then rendered and executed by the victim's browser. This can lead to XSS attacks, manipulation of website appearance and behavior, or unauthorized access to sensitive information.


The impact of CSS Injection vulnerabilities can be severe, leading to security risks such as XSS attacks, website defacement, or compromise of user accounts within our application. Attackers can exploit these vulnerabilities to execute arbitrary code in the context of the victim's browser, manipulate website content, or steal sensitive information, potentially resulting in financial loss, reputational damage, or legal consequences for our organization.


The likelihood of exploitation depends on various factors, including the visibility and accessibility of user-controllable input within our application, the security measures implemented to validate and sanitize input, and the attacker's knowledge and motivation. However, given the prevalence of XSS vulnerabilities in web applications and the potential impact on website integrity and user security, the risk associated with CSS Injection is significant if not properly mitigated.

Steps to Reproduce:

  1. Identify user-controllable input fields or URL parameters within our application that are used to generate CSS code.
  2. Inject malicious CSS code, such as JavaScript snippets or style overrides, into these input fields or parameters.
  3. Submit the manipulated input to the server and observe if the injected CSS code is rendered and executed by the victim's browser.
  4. Determine if attackers can exploit CSS Injection vulnerabilities to execute arbitrary code, manipulate website appearance, or steal sensitive information within our application.

Recommendations for Developers:

  1. Implement Input Validation: Validate and sanitize user-controllable input to prevent injection of malicious CSS code.
  2. Use Content Security Policy (CSP): Implement a Content Security Policy to restrict the sources from which CSS can be loaded or executed, mitigating the risk of CSS Injection attacks.


Addressing CSS Injection vulnerabilities is critical to protecting against XSS attacks, website defacement, and compromise of user security within our application. By implementing input validation and using Content Security Policy, we can mitigate the risks associated with CSS Injection and enhance the overall security posture of our systems.