xss-html-injection_skill

Overview

This skill describes a structured approach for assessing client-side injection risks like cross-site scripting (XSS) and HTML injection in web applications. It focuses on safe detection, classification, and remediation guidance rather than providing exploit recipes. Use it to evaluate input handling, output encoding, and client-side code that may introduce injection flaws.

How this skill works

The skill guides a tester through discovery, confirmation, and reporting phases: identify where user input is reflected or stored, determine whether issues are server-side, reflected, or DOM-based, and validate findings with controlled, non-destructive checks. It emphasizes use of browser developer tools, request inspection, and safe proof-of-concept techniques that avoid exfiltrating real user data.

When to use it

• During security assessments of web applications with user inputs
• When validating fixes for XSS or HTML injection reports
• Before deployment to verify frameworks and templating escape outputs
• When reviewing client-side JavaScript that processes URL fragments or user-controlled data
• When assessing Content Security Policy (CSP) and other browser defenses

Best practices

• Obtain written authorization and define a clear testing scope before any testing
• Avoid destructive payloads and do not exfiltrate real user data or credentials
• Prefer non-persistent, observable tests; capture only metadata required for reproduction
• Use browser consoles, safe captive test accounts, and isolated staging environments where possible
• Document reproduction steps, affected parameters, and recommended fixes (output encoding, input validation, CSP improvements)

Example use cases

• Assessment of a comment system or user profile fields for persistent injection risks
• Review of search and query parameters that reflect input into pages
• Audit of single-page app code that inserts URL fragments or query values into the DOM
• Validation of CSP and cookie attributes after a remediation patch
• Pre-release security checklist for templating and client-side rendering changes