Stored Cross-Site Scripting (Stored XSS)

Executive Summary:

This report details a Stored Cross-Site Scripting (Stored XSS) vulnerability discovered within our web application. Stored XSS is a severe security issue where an attacker injects malicious scripts into the web application, which are then permanently stored and executed in the browsers of other users. This document aims to concisely present the nature of the vulnerability, assess its potential impacts, and offer developer-centric recommendations for remediation.

Description of the Vulnerability:

Stored Cross-Site Scripting occurs when user input containing malicious scripts is saved by the web application and then displayed to other users. The vulnerability was identified in the [specific feature/module] where user input, specifically through the [specific input field or functionality], is not properly sanitized before being stored and subsequently rendered in other users' sessions.


The impact of a Stored XSS attack can be significant, allowing attackers to perform actions on behalf of other users, access sensitive information, propagate malware, or redirect users to malicious sites. It compromises not only the security of individual users but also the overall trust in our platform.


The likelihood of exploitation is high due to the persistent nature of Stored XSS, where the malicious script remains within the application until explicitly removed. This type of vulnerability is particularly insidious as it can affect multiple users over an extended period without detection.

Steps to Reproduce:

  1. Go to [specific module/page].
  2. In the [specific input field or functionality], enter a malicious script, for example: <script>alert('Stored XSS')</script>.
  3. Submit or save the input.
  4. Navigate to a section of the application where the submitted data is displayed to the user.
  5. Observe that the script is executed, indicating a Stored XSS vulnerability.

Recommendations for Developers:

  1. Implement Input Sanitization: Ensure that all user input, especially in [specific input field or functionality], is sanitized before being stored or rendered. Utilize a library or framework that specifically addresses XSS vulnerabilities.
  2. Use Context-Sensitive Encoding: Apply appropriate encoding when displaying user-generated content, based on the context (HTML, JavaScript, CSS, etc.) to neutralize potentially malicious code.
  3. Content Security Policy: Adopt a strong Content Security Policy (CSP) to add an extra layer of protection, preventing the execution of unauthorized scripts.


Addressing this Stored XSS vulnerability is imperative to protect our users and maintain the integrity of our application. By implementing the recommended preventative measures, we can significantly mitigate the risk of future XSS attacks and enhance the security posture of our web application.