| name | testing-for-xss-vulnerabilities |
| description | Tests web applications for Cross-Site Scripting (XSS) vulnerabilities by injecting JavaScript payloads into reflected, stored, and DOM-based contexts to demonstrate client-side code execution, session hijacking, and user impersonation. The tester identifies all injection points and output contexts, crafts context-appropriate payloads, and bypasses sanitization and CSP protections. Activates for requests involving XSS testing, cross-site scripting assessment, client-side injection testing, or JavaScript injection vulnerability testing.
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| domain | cybersecurity |
| subdomain | penetration-testing |
| tags | ["XSS","cross-site-scripting","client-side-security","OWASP-A03","JavaScript-injection"] |
| version | 1.0.0 |
| author | mahipal |
| license | Apache-2.0 |
| nist_csf | ["ID.RA-01","ID.RA-06","GV.OV-02","DE.AE-07"] |
Testing for XSS Vulnerabilities
When to Use
- Testing web applications for client-side injection vulnerabilities as part of OWASP WSTG testing
- Evaluating the effectiveness of input sanitization and output encoding across all application features
- Assessing the protection provided by Content Security Policy (CSP) headers against XSS exploitation
- Demonstrating the impact of XSS through session hijacking, credential theft, or phishing overlay to stakeholders
- Testing single-page applications (React, Angular, Vue) for DOM-based XSS in client-side routing and rendering
Do not use against applications without written authorization, for deploying persistent XSS payloads that affect real users, or for exfiltrating actual user session tokens from production environments.
Prerequisites
- Authorized scope defining the target web application and acceptable testing activities
- Burp Suite Professional with XSS-focused extensions (XSS Validator, Reflector, Active Scan++)
- Browser with developer tools and XSS testing extensions (HackBar, XSS Hunter)
- XSS Hunter or Burp Collaborator for out-of-band payload verification
- SecLists XSS payload lists and custom payloads for WAF bypass scenarios
Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.
Workflow
Step 1: Input and Output Mapping
Map every location where user input enters and is rendered by the application:
- Reflected inputs: Test every URL parameter, search field, error message, and HTTP header value that is reflected in the response
- Stored inputs: Identify features where input is saved and displayed later: user profiles, comments, forum posts, file names, support tickets, and chat messages
- DOM inputs: Identify client-side JavaScript that reads from
location.hash, location.search, document.referrer, window.name, postMessage, or localStorage and writes to the DOM
- Output context identification: For each reflected input, determine the rendering context:
- HTML body:
<div>USER_INPUT</div>
- HTML attribute:
<input value="USER_INPUT">
