Cross Site Request Forgery: How it Works and How to Prevent It?

Quick Summary: This article will give you deep insights into Cross-site Request Forgery and how it impacts users and organizations. It is a critical security risk that tricks users into performing actions they don’t intend to by misusing their sessions. Learn more about it and ensure a strong security posture.

Whether you are a CISO or a security expert, acquiring knowledge of potential web app security risks is critical for creating secure digital solutions. Users engage with a web application and share their data only when they trust it.

Keeping that trust intact requires an understanding of the threat landscape and practices to mitigate security risks. One of the most important threat vectors is Cross-site Request Forgery or CSRF. With a CSRF attack, a bad actor can compel a user to perform an unwanted action.

The resulting action can be to delete some data, change a password, make a financial transaction, or more. Understanding what CSRF is and how it occurs can help you protect your web applications more effectively.

In this article, CSRF is explained in detail providing the information you need to understand it and defend against it. Besides, you can also find some ways to prevent this threat and learn how a vulnerability assessment tool is helpful in protecting against it.

Keep scrolling for an informed decision.

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What is Cross-Site Request Forgery (CSRF)?

Cross-Site Request Forgery aka CSRF, XSRF, Session Riding, or Cross-site Reference Forgery, is one of the most critical cyberattack tactics. In this type of attack, a bad actor tricks a user into performing an undesired action on a web application they are authenticated with.

On top of that, these undesired actions are state-changing actions like altering passwords or email addresses, transferring funds, and more. Therefore, CSRF is among the most serious web app security risks that can affect individuals and organizations.

Imagine you are logged into your bank’s website and there is an unintentional transaction made from your account to someone, say to Bob. This transaction wasn’t initiated by you, and you are scratching your head pondering how it happened.

In this situation, you might be a victim of Cross-site Request Forgery (CSRF). But how does this happen? How can a fund transfer transaction be initiated without your knowledge? Your mind would be bombarded with these questions. Right?

The following section will help you understand how it could happen.

Common Cross-Site Request Forgery Vulnerabilities

Let’s learn about common types of CSRF vulnerabilities that can lead to many potential attacks in web applications.

Less Secured State-Changing Requests

When web applications fail to verify that requests originate from the authenticated user, attackers can easily misuse this by creating malicious requests to change user settings or perform actions like transferring funds or altering account details. This happens because the application is dependent on the user's session or cookies for authentication without comprehensive checks.

Absence of Anti-CSRF Tokens

Anti-CSRF tokens are unique codes that websites insert in forms and APIs request for verification of user requests’ authenticity and legitimacy. If these tokens go missing or are not used in a proper way, then attackers wait for such situations to manipulate users into submitting requests from a different website by bypassing security checks.

Lack of Same-Site Cookies

Cookies are small pieces of data stored by a browser. The SameSite features allows preventing cookies from being sent with requests initiated from other sites. If SameSite feature does not exist, there are chances of cookies being sent with malicious data from different unreliable websites. This enables attackers to perform actions on behalf of the user without their approval.

Insecure HTTP Methods

GET requests are typically used to redeem data stored by a browser and it is not supposed to be used for actions that change data (like submitting forms). If web applications use GET requests to perform such actions, then attackers get a chance to manipulate users into clicking on a link that performs these actions by exploiting the vulnerability.

Guessable URLs

If URLs for performing serious actions (like changing a password) are easy to guess, then attackers can create their own requests targeting these URLs. For instance, if a URL has simple number sequence (e.g., /update-profile?id=123), attackers might try different numbers to access or alter other users’ data.

How Does Cross Site Request Forgery Attack Work?

For a CSRF attack to be successful, a bad actor needs to trick a user into taking an unintentional action. How can it be done? Well, the best way to do this is through social engineering. The overarching goal of social engineering is to leverage psychological manipulation to trick users into providing their confidential information or login credentials.

In the case of CSRF, a bad actor exploits the trust a web application has in a user already authenticated with it. So, if a web application only uses cookies to identify a user, a bad actor can take advantage of this cookie-based authentication to trick users into performing unwanted actions.

Since the user is already logged in with a valid cookie the web application will normally complete the action. The bad actor can use a crafted URL to dupe users into taking such actions. This URL can be delivered through an email with a forged webpage disguised as a bank’s mail.

In this CSRF attack example, a bad actor also overcomes the same-origin policy of web browsers. Usually, browsers follow a same-origin policy that restricts access from one domain to another domain. It means a user cannot open a link if it doesn’t originate in the same domain.

However, with the CSRF vulnerability, the browser sends the request to the bank’s server with no complaint. A real-life example of CSRF is vulnerabilities in CISCO’s Expressway and ClamAV.

Let’s understand how this attack unfolds with a practical cross site request forgery attack example.

Suppose a person named Sarrah wants to transfer $1000 to Bob through the bank’s web application at examplebank.com. The web application is vulnerable to CSRF.

Now let’s look at the attack method based on different scenarios.

Scenario 1: If the web app uses the GET method:

In this case, the request for transferring money might look as follows:

GET https://examplebank.com/transfer.do?account=SARRAH&amount=1000 HTTP/1.1

A bad actor named Alice wants to use a CSRF exploit to transfer money, say $1000, to her account. For this, she fabricates a URL by replacing the name in the original link with her own. So, she uses the link:

https://examplebank.com/transfer.do?account=ALICE&amount=1000

Now, with the use of social engineering tactics like planting the link in a web page that Sarrah may visit when using the banking application or sending it via an unsolicited email, Once Alice successfully tricks Sarrah into loading this link that amount will be transferred to Alice’s account.

Scenario 2: If the web app uses the POST method:

Now, the funds transfer request will look like this:

POST https://examplebank.com/transfer.do HTTP/1.1

This type of request is delivered through forms instead of “<a>” and “<img>” tags. So, the bad actor will craft a form such as:

<form action="http:/examplebank.com/transfer.do" method="POST">  <input type="hidden" name="acct" value="ALICE"/>  <input type="hidden" name="amount" value="1000"/>  <input type="submit" value="Check pictures"/>  </form>

Now, this can be sent to the victim user (Sarrah in this case), and it will be executed once the “Submit” button is clicked. It can also be executed automatically with a JavaScript code like:

<body onload=”document.forms[0].submit()”>  <form ....

So, this is how CSRF takes place and how victims fall prey to it. Moreover, it is a serious security risk, especially for those found on the OWASP Top 10.

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A Quick Comparison of CSRF vs SSRF vs XSS

Often, CSRF is confused with SSRF and XSS. SSRF or Server Side Request Forgery occurs due to web application vulnerability that allows a bad actor to force a web app to make requests to an unwanted location. This means that, in this case, a bad actor attempts to connect a web app to an external server. It is also mentioned in the OWASP vulnerability checklist, which makes it a critical security risk for organizations.

XSS or Cross-site Scripting attack allows a bad actor to inject client-side code or script. This code or script is executed when a user visits the web page embedded with such script or code. With this attack, a bad actor can steal the credentials of a victim user.

However, in each case, the bad actor must bypass the cross-origin policy of web browsers. Further, social engineering is also used in each of these cases.

CSRF, XSS, and SSRF all lead to disastrous consequences for organizations and users. Organizations need to choose the best web app security practices and other measures to protect their data and users from these threats.

What are the Consequences of a CSRF Attack?

Any kind of cyberattack is always a risk to an organization that affects its business, users, and digital assets. Hence, understanding the impact of CSRF is no rocket science. It is as bad as an SQL injection or any other type of attack.

The following are the consequences of a successful cross-site request forgery attack.

Data Manipulation

A bad actor can exploit the trust a web application has in authenticated users to carry out CSRF attacks. In this case, web apps cannot distinguish between legitimate users and users with crafted requests. As a result, the bad actor can force users to send state-changing requests. This request could be related to modifying data, like deleting or adding new information.

Server Control

A bad actor can take over a server’s control by sending a state-changing request that could modify configuration settings. It can happen when the targeted user has administrative privileges. This will allow the bad actor to access unauthorized data and resources.

Malware Installation

Another critical security concern is the installation of malware on the target server. A bad actor may exploit web application vulnerabilities to install ransomware on the host server. It will lock your essential data and resources until a certain amount is paid to the bad actor. The data will be encrypted with a strong key, which will make it hard to recover the data.

Reputational Damage

A cross-site request forgery attack can also cause reputational damage due to an incident of data breach. It will impact your business. Consequently, it will be hard for you to acquire new customers and retain the existing ones.

What are Some Ways to Prevent the CSRF Attack?

Cross-site request forgery is a common attack vector that bad actors use for online fraud. The ensuing threats can be mitigated with various measures, including vulnerability management, to discover and resolve security flaws. Let’s check out all the measures to eliminate this cyber threat.

CSRF Token

One way to defeat the threat of cross-site request forgery is using a CSRF token. This will be a large, random, unpredictable token that will be used to validate whether the HTTP request is sent from a legitimate user. When the HTTP request is received, the token is verified to ensure it’s a genuine request. The server can verify this token from the HTTP request header.

SameSite Cookie Attribute

You can leverage the SameSite browser attribute for cookies that determines when to include a website’s cookies in the request for another site. It is an effective CSRF defense that restricts unknown websites from accessing cookie data. Since performing sensitive actions requires cookie data, you can minimize the ensuing risks by setting the SameSite attribute. It can be set to “Lax” or “Strict” and you can choose appropriately.

Security Testing

Web app security testing is a robust method to ensure optimal web app security. It involves evaluating your web application for common vulnerabilities to identify potential risks. It will also help to discover CSRF vulnerabilities and remediate them to protect your web app from such threats.

To achieve the security testing goal, you need a robust vulnerability scanning tool that will help you uncover vulnerabilities accurately. These scanners are designed to detect common security flaws in web apps including those defined by the Open Web Application Security Project (OWASP).

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Tighten Your Web App Security with ZeroThreat

CSRF is one of the most notorious cybersecurity risks that will adversely affect your organization and users. However, you can leverage vulnerability assessment to identify potential security weaknesses that lead to such threats.

This is a strategic approach to scan web apps for vulnerabilities, prioritize detected vulnerabilities, and remediate them to enhance security posture. This is what you can achieve with ZeroThreat. It is a feature-rich web application security testing tool.

You can discover a wide range of vulnerabilities with ZeroThreat, including CSRF and fix them to make your web app secure for end users. The best thing about it is that it can detect vulnerabilities with zero false positives and scan web apps at a faster speed.

You can try it for $0 with no credit card requirement to test its abilities.