Day 20 — A Deep Dive into Open Redirect Vulnerabilities in Flask – From Exploitation to Ironclad Fixes

In the world of web security, vulnerabilities often lurk in the seemingly innocuous corners of your code—like a simple redirect that trusts user input a little too much. Open Redirects are one such "simple" issue, but their impact can ripple into phishing epidemics, credential theft, and OAuth hijackings. In this detailed writeup, we'll dissect the vulnerability step by step: what it is, why it happens in Flask apps, how attackers weaponize it, and—most importantly—how to fortify your code against it. I'll include expanded code examples, real-world attack vectors, and even a quick lab setup to test it yourself. If you're a developer dipping into security or a pentester honing your skills, this is your hands-on guide. Let's build, break, and bulletproof a Flask app together. What is an Open Redirect Vulnerability? At its core, an Open Redirect (also known as an unvalidated redirect) happens when a web application allows user-supplied input to dictate where a user gets redirected without