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Introduction
Modern web applications fail not because developers ignore security, but because they overtrust user-supplied data. Attackers exploit this trust by injecting malicious payloads, manipulating object references, and bypassing access controls—turning everyday features into breach vectors. Understanding how these exploits work in practice is the difference between a passing vulnerability scan and truly resilient application security.
Learning Objectives
– Identify and exploit common web vulnerabilities including XSS, IDOR, SSRF, and JWT misconfigurations using manual testing techniques.
– Implement effective mitigations through input validation, authorization checks, and secure session management on both Linux and Windows environments.
– Apply step‑by‑step penetration testing commands and configurations to uncover broken access controls and API endpoint flaws.
You Should Know
1. Cross‑Site Scripting (XSS) – From Reflected to DOM‑Based
XSS occurs when untrusted data is rendered as code in a victim’s browser. Attackers inject scripts that steal sessions, deface pages, or redirect users. The key is understanding where user input reaches dangerous sinks like `innerHTML` or `eval()`.
Step‑by‑step guide to test and mitigate XSS:
– Test for reflected XSS: Use `curl` to inject a payload into a URL parameter.
curl "http://testapp.com/search?q=<script>alert('XSS')</script>"
– Test for stored XSS (Linux): Submit a POST request with a payload via `curl -X POST -d “comment=” http://testapp.com/post/123`
– Windows PowerShell alternative:
Invoke-WebRequest -Uri "http://testapp.com/search?q=<script>alert('XSS')</script>" -Method GET
– Mitigation (code example): In Python Flask, use `escape()` from `markupsafe`; in Node.js, use `helmet` and output encoding libraries.
– WAF rule (ModSecurity): Block script tags in parameters: `SecRule ARGS “