CORS - Misconfigurations & Bypass

👉 Overview

👀 What ?

Cross-Origin Resource Sharing (CORS) is a security mechanism that allows specified, trusted domains to access resources on a web page of a different domain. Misconfigurations in CORS can lead to security vulnerabilities, making it possible for attackers to bypass the security measures and access sensitive data.

🧐 Why ?

CORS is an essential feature in modern web applications. However, if CORS is not correctly configured, it can expose the application to security risks. Misconfigurations can enable a malicious website to make requests to the target website and read the responses, leading to potential data breaches. Therefore, understanding CORS, its misconfigurations, and how to bypass them is crucial for both web developers and cybersecurity professionals.

⛏️ How ?

To take advantage of CORS or implement it properly, you need to understand its core concepts. The essential step in CORS is the preflight request, which is a mechanism that checks whether the cross-origin request is safe. If CORS is misconfigured, an attacker could bypass the preflight request and make direct requests to the server, potentially accessing sensitive data.

⏳ When ?

CORS was introduced with the XMLHttpRequest Level 2 specification around 2014 as a way to make requests across different origins, which was not possible with the traditional same-origin policy enforced by web browsers.

⚙️ Technical Explanations

At a technical level, CORS works by adding new HTTP headers that allow servers to describe the set of origins that are permitted to read that information using a web browser. If the server does not include the appropriate headers in its response, or if the server does not permit the request from the specific origin, the browser will block the request. Therefore, if CORS is misconfigured and the server responds with incorrect headers, the browser could potentially allow a malicious request.