As bug bounty hunters, we often traverse the cyber wilderness seeking vulnerabilities that may lead us to a pot of gold (quite literally, if we consider bug bounty programs!). Today, let’s dive into an area that offers the thrill of the chase and the potential for bigger rewards — vulnerability chaining.

We will dissect this intriguing concept to understand how seemingly unrelated security flaws can be linked together to craft a more severe exploit. So strap in, as we are about to delve deep into the fascinating world of vulnerability chaining.

Vulnerability chaining, often also called exploit chaining, refers to the practice of exploiting multiple vulnerabilities, usually in a sequential manner, to breach or compromise a system or network. It’s akin to finding separate weak links in an otherwise strong chain, then using those weak points in unison to break the chain apart.

The impact of a single vulnerability may range from trivial to critical. However, when vulnerabilities are chained together, their combined effect can be catastrophic, often far exceeding the impact of the individual vulnerabilities. For attackers, it’s like turning a set of small keys into a master key for greater access.

Let’s dive into a step-by-step example of a typical vulnerability chain — escalating from Cross-site Scripting (XSS) to Cross-Site Request Forgery (CSRF) to an account takeover.

Step 1: Identifying an XSS vulnerability

Our journey begins with a common but powerful vulnerability — XSS. We find a website where user input is reflected in the website’s HTML without proper sanitization or output encoding, allowing us to inject malicious scripts that can be executed in other users’ browsers.

Step 2: Crafting the XSS payload