xss
What is XSS?
XSS stands for Cross-Site Scripting. It’s a type of cyber attack where a hacker tricks a website into running harmful code in someone else’s browser. The goal is to steal information, mess with what the user sees, or even take control of their account.
Think of a website as a stage. Normally, only safe, expected things are allowed to happen on that stage. But with XSS, an attacker sneaks in a script (a little program) and convinces the stage to run it, often without anyone noticing.
XSS vulnerabilities are included in the OWASP Top 10 as critical types of injection vulnerabilities.
How does XSS work?
XSS works by taking advantage of websites that show user input without checking it. For example, if a comment section lets someone post JavaScript code, that script could run when another visitor views the page.
If the attacker’s code can run, it might grab your cookies (which can include login info), change what you see, or send you to a phishing site. It’s sneaky and often invisible.
What is the primary goal of an attacker using XSS?
The main goal is to hurt users by stealing their data or tricking them. Common risks include:
- Stealing login credentials
- Stealing sensitive information
- Hijacking user accounts
- Changing the content or functionality of a website
What are the different types of XSS?
There are three main types of XSS vulnerabilities:
- Stored XSS - the script is permanently stored on a website.
- Reflected XSS - the script shows up only when a user clicks a specific link.
- DOM-based XSS - the attack happens in the browser when a page’s code is changed on the fly.
How is XSS similar to SQLi?
XSS and SQL injection (SQLi) are both types of injection attacks. They happen when attackers send unexpected code into a website. With SQLi, the goal is to attack the website’s database. With XSS, the goal is to attack the user’s browser.
How to fix a XSS vulnerability
Fixing XSS involves using two main layers of defense.
First, user input should be validated as strictly as possible when it arrives. This means checking that the data looks like what it’s supposed to be.
For example:
- A name should only include letters and a few basic symbols.
- A year of birth should be exactly four numbers.
- An email address should match a standard pattern.
If the input doesn’t pass these checks, it should be rejected completely - not just cleaned up.
Second, user input should be HTML-encoded anywhere it gets displayed back on the website. This means turning special characters like <, >, ", ', and = into safe versions that can’t be used to write code. For example, < becomes <, which shows the symbol without letting it act like code.
Together, these steps make it much harder for attackers to insert scripts into your site.
How to prevent XSS
XSS vulnerability scanners can be used to find XSS vulnerabilities, such as Intruder.
With Intruder, the first thing you need to do is add your applications as targets by entering IP addresses or URLs. You can then kick off your first scan in just a few clicks – it’s that simple!
Once your scan is complete, you will see a list of issues. You can search for ‘XSS’ in the search bar to see if this type of vulnerability is present, and if so, which target(s) it affects.
