Cyberdudebivash

        CRITICAL XSS FLAW: Insecure Output Handling Puts Your Entire Web App at Risk (The Fix)     By CyberDudeBivash • September 27, 2025 • AppSec Developer Guide   There is a fundamental rule of web security that is being broken every day, leading to one of the most persistent and dangerous vulnerabilities on the internet: **never trust user input**. The failure to properly handle data submitted by users before rendering it back on a page—a flaw known as Insecure Output Handling—is the root cause of Cross-Site Scripting (XSS). This isn't a new threat, but it remains a top vulnerability precisely because it's so easy to get wrong. An attacker who finds a single XSS flaw can hijack your users' sessions, steal their credentials, deface your website, and deliver malware, all from the trusted context of your own domain. This is a deep-dive for developers and security professionals on how this attack works, the different types of XSS, and the essen...