Cross-Site Request Forgery, often called CSRF (or its other nicknames, Session Riding and XSRF), is a tricky type of attack. In short, it lets attackers make users do things on websites without their consent or knowledge. This attack works by misusing the trust a web application puts in a user’s browser once they’re logged in. By duping the browser into sending fake requests (usually through shady emails or misleading links), CSRF allows unauthorized commands to hit a website. And since these requests seem to come from a legitimate, logged-in user, the website has a hard time spotting the fakes, which can open the door to significant security problems.
Below we’ll cover how these attacks happen, their impact, and proven methods to keep your web apps secure.
How Does Cross-Site Request Forgery Work Its Magic?
So, how does a CSRF attack actually pull it off? Well, three things usually need to be in place. First, the attacker needs to target an action that can be done with a simple web request – think things like changing account details or admin settings. Second, the website has to rely only on session cookies to know who’s making the request, without any extra checks. Third, the attacker needs to be able to guess what the mischievous request should look like. Then, if all these pieces fit, the attacker just has to get that bogus request (often hidden in a link or some web content) over to the victim’s browser so it can do the dirty work.
Here’s a CSRF Attack in Action (An Example)
Let’s say you get an email that looks like it’s from customs, saying a package for you is stuck and you need to click a link to sort it out. You click, and it takes you to a website you commonly use, maybe even your own. Everything seems fine on the surface. But, what if a part of that website, like a plugin you installed, has a CSRF weakness?
For example, imagine a music plugin that doesn’t properly check who’s allowed to change its settings. An attacker could create a special link, something like www.yourwebsite[.]com/music/settings?default_user=admin&anyonecanregister. If an admin of your site clicks that link while they’re logged in, it could quietly change the settings to let anyone sign up as an admin! The attacker would hide this link in that fake customs email. The admin clicks, and bam – they’ve unknowingly given the attacker control. This really shows why good security, like using CSRF tokens and checking where requests come from, is a big deal. And remember, CSRF isn’t about cookies alone; it can pop up anywhere an app automatically trusts user credentials.
CSRF vs. XSS: What’s the Difference?
It’s easy to mix up CSRF with another common threat, Cross-Site Scripting (XSS), since both try to run bad code during your web session. But they go about it differently. XSS is all about sneaking harmful scripts right onto a web page you’re looking at. That script then runs in your browser as if it’s part of the site, potentially letting attackers grab whatever’s on the page, even anti-CSRF tokens.
CSRF, on the other hand, plays on the trust between your browser and a website. It usually involves tricking users into making their browser send a fake request to a site they’re logged into. This request often comes from a dodgy page or link the attacker controls. A key difference? With CSRF, the attacker usually doesn’t get to see what the website sends back. But here’s a kicker: if a site has an XSS problem, even good CSRF protection might not be enough because XSS could swipe that anti-CSRF token.
The Damage of a CSRF Attack
When a CSRF attack hits the mark, it can cause a lot of trouble for everyone involved, from businesses to everyday users. We’re talking about things like money being moved without permission, passwords getting changed (which can mean accounts get hijacked), and private data, even session cookies, being stolen. Attackers usually pull this off by luring people to a harmful page or getting them to click a specially made link that takes advantage of a weak spot on the target website. This click sends requests through the user’s browser, and because the user is logged in, everything looks legit.
How bad is it? Well, that often depends on who gets hit. If it’s a regular user, the damage might be contained. But if an admin gets targeted, the whole website could be in deep trouble.
How to Prevent Cross-Site Request Forgery
Preventing CSRF isn’t always straightforward since attacks can be tailored, but a mix of smart user habits and strong website defenses can cut down the risk.
What Users Can Do
Okay, so while it’s mostly up to the website builders to stop CSRF, users can do a few things to stay safer:
- Make sure you’re using strong, different passwords for all your accounts (don’t reuse them).
- Always log out of websites when you’re done, especially the important ones like your bank account, stock apps, socials, etc.
- Think twice before letting your browser save your passwords. And be super careful about clicking on links or opening attachments in emails if you don’t know who sent them or if they look fishy.
What Website Builders Need to Do
For the folks building websites, here’s how you can fight back against CSRF:
CSRF Tokens are Your Best Friend
This is a big one. The website creates a special, secret, unpredictable code (the CSRF token) for each user or important action. This token gets hidden in web forms or sent along with web requests. When you do something important, say submit a form, your browser has to send that token back. The website checks it, and if it’s missing or wrong, no dice – the request gets rejected. This stops attackers because they’re left to guessing the right token.
Use the SameSite Cookie Setting
This is a neat browser feature that tells cookies when they should (and shouldn’t) be sent along with requests that come from other websites.
Strict: This is super safe. It tells the browser not to send the cookie if the request comes from anywhere else, even if you just clicked a normal link. It’s great for security but can sometimes mess with how users navigate between sites.Lax: This is a good middle ground. It lets cookies go with regular link clicks and safe (GET) requests from other sites but blocks them on riskier requests like when data is being sent (POST/PUT/DELETE). Most browsers now use Lax by default, which is a nice security boost. Getting this setting right for your session cookies really helps shut down CSRF.
Check the Referer Header (With a Grain of Salt)
Some sites try to check the Referer header, which tells them where a request came from. If it’s not from their own domain, they might get suspicious. It’s an extra layer, but don’t rely on it alone because this header can sometimes be missing or even faked.
Set Up Cross-Origin Resource Sharing (CORS) Wisely
CORS is how servers tell browsers which other websites are allowed to ask for their resources. While it’s mainly for letting good cross-site requests happen safely, good CORS rules can also help stop CSRF. Browsers will check these rules and block requests from unauthorized places, especially for things like API calls that try to change data.
Mixing these methods, especially CSRF tokens and SameSite cookies, gives you a pretty solid defense. For really important stuff, making users re-enter their password or solve a CAPTCHA can add even more protection.
Wrapping It Up
So, there you have it. Cross-Site Request Forgery is the kind of web attack that really shows why good security habits matter. It takes advantage of your trust and your logged-in status to make you do things online you never intended, and that can lead to some big problems. Tackling CSRF also isn’t a one-person job; it takes teamwork. Website developers need to build strong defenses, like using tokens and SameSite cookies. Users need to be smart about how they browse the web. Attackers are always coming up with new tricks, so staying alert, coding securely, and knowing the risks are key to keeping everyone safer online.
Cesar Anjos
Luke Leal
Gerson Ruiz
Denis Sinegubko
Rianna MacLeod
