What is CSRF and How Does It Work?

Often, when people think of hackers, they imagine someone breaching a network to steal large volumes of sensitive data. However, many hackers nowadays exploit vulnerabilities in individual user interactions with trusted websites. One such method is cross-site request forgery (CSRF)—a type of attack that manipulates users into performing unintended actions on websites where they’re already authenticated. This approach typically leverages social engineering to trick users into executing malicious requests, often without even realizing it. CSRF is recognized as a significant OWASP Top 10 threat, commonly used by threat actors and malicious websites to exploit trusted user sessions and carry out unauthorized actions on their behalf.

It’s more important than ever to know what to look for when dealing with these harmful cyberattacks. Let’s dive into what CSRF attacks are, how they work, and how you can protect your website from this rising security vulnerability.

What is a CSRF attack?

Cross-site request forgery attacks occur when a hacker tricks a user into performing unwanted actions on a trusted website or web application. This is done by exploiting the user's active authentication session, such as session cookies or authentication tokens.

Unlike attacks that steal sensitive data directly, CSRF takes advantage of the trust that a website places in the victim’s browser. When a user is logged into a website, CSRF exploits their authenticated session to send forged requests on their behalf, without the user’s knowledge or consent, triggering harmful actions and making it difficult for the website to distinguish between legitimate and malicious requests.

Types of CSRF attacks

There are several types of CSRF attacks, with varying impacts based on the attacker’s level of access and goal:

• Standard CSRF: This type exploits authenticated users by tricking them into performing actions, such as changing their account information or making unauthorized purchases.
• Login CSRF: In this attack, a non-authenticated user is manipulated into logging into a site under the attacker’s control. This could lead to the access of sensitive data by hackers if the victim adds private information.
• State-Changing CSRF: These attacks involve performing actions that change the state of an application, such as transferring funds or changing security settings.

How does CSRF work?

Typically, a CSRF attack is carried out with the help of social engineering. The attacker sends a malicious link via email, text message, or voicemail, tricking the user into clicking it. Once the user clicks the link, the attacker inherits the user's identity and authentication privileges, using them to perform unauthorized actions on the user’s behalf. This can include sending a sensitive URL or code snippet to the victim, prompting them to execute an unintended request, such as changing their account settings or email address to one the attacker controls.

While cross-site scripting (XSS) attacks trick users into revealing sensitive information, CSRF focuses on manipulating the user’s interaction with a trusted website to make unwanted changes. Rather than stealing data, CSRF exploits the user’s credentials to send forged requests, often without the user realizing it. What makes CSRF particularly dangerous is that browser requests automatically include credentials associated with the site—such as session cookies or authentication tokens. So, when the victim is logged into a website at the time of the attack, the site has no way to distinguish between legitimate requests and forged ones. If an admin account is targeted, the hacker may even gain control of the entire website or application.

The attacker doesn’t just manipulate the victim; they also exploit the website’s trust in the user’s browser session. This allows them to carry out actions like changing account settings, making unauthorized purchases, or even transferring funds without the victim’s knowledge. The malicious request appears legitimate because it is made using the victim’s authenticated session, making it difficult for the website to detect that it is a forgery.

For example, consider a scenario where you’re logged into your online banking account. If an attacker sends you a malicious link and you unknowingly click it, your browser might submit a request for fund transfers from your account to theirs. Since you’re authenticated on the bank’s website, the request will look legitimate, and the bank may process it without suspicion.

Testing for CSRF vulnerabilities

To test for CSRF vulnerabilities, you can check whether sensitive requests (like deleting an account or changing a password) can be triggered by simply visiting a URL directly, instead of requiring user interaction (like clicking a button). A vulnerable site might allow such a request to execute just by visiting a link, indicating a potential vulnerability.

For instance, imagine a website that offers a "delete account" option. The URL for deleting an account might look like this:

http://www.example.com/delete-account?user=12345

If this URL can be accessed directly, it’s likely vulnerable to a CSRF attack. A hacker can exploit this by sending the victim a link containing this URL, triggering the action without their consent.

It’s also essential to consider other vectors for CSRF, such as hidden forms automatically submitted via JavaScript or embedded in images (like <img src="http://attacker.com/maliciousrequest">), which can execute actions on the victim’s behalf.

Consequences of CSRF attacks

A successful CSRF attack can have devastating consequences. Beyond compromising individual user accounts, these attacks can escalate to admin account access, allowing attackers to gain full control over a website or application.

Some potential consequences include:

• Account Hijacking: Unauthorized changes to a user’s account, such as modifying personal details or making purchases.
• Data Loss: Deletion of important user data or configuration changes, which can affect a website’s functionality.
• Reputation Damage: If a CSRF vulnerability is exploited, the target website may face downtime or suspension from web hosts, further eroding user trust. Moreover, web browsers like Google Chrome or antivirus software may flag the site as insecure, potentially leading to blacklisting and traffic loss.

Mitigating CSRF attacks

There are several ways to mitigate CSRF vulnerabilities, including both preventative measures and the use of specialized tools:

1. CSRF Tokens: A CSRF token is a unique, unpredictable value assigned to each user session. This token must be included in each request sent by the user. If the server detects a mismatch between the session token and the request token, it rejects the request, effectively blocking CSRF attacks.

• Synchronizer Token Pattern: A common method for CSRF protection is to use a synchronizer token that is included in the form submission, ensuring that only legitimate requests are processed.
• Challenge Token Pattern: Another approach is a challenge token, where the server generates a token and checks the incoming request for validity.
• Anti-CSRF Tokens: These tokens are added to each request and must match a value stored on the server, preventing unauthorized access and malicious requests.

2. Referrer and Origin Header Validation: This method involves validating the referrer header in HTTP requests to ensure that requests originate from the expected source. Requests coming from outside the intended domain, such as an email link or an attacker’s website, can be blocked.

3. SameSite Cookie Attribute: Implementing the SameSite cookie attribute ensures that cookies (including session cookies) are not sent in cross-site requests, adding an additional layer of protection against CSRF.

4. Use Secure Authentication: Implementing secure authentication methods, like multi-factor authentication (MFA), can reduce the effectiveness of CSRF, as attackers would still need to compromise the second authentication factor.

Prevent CSRF attacks with SiteLock solutions

CSRF attacks continue to be a significant cybersecurity risk because they can exploit user sessions and bypass traditional defenses. To protect your site from these vulnerabilities and more, it's essential to take preventative steps like using CSRF tokens, validating referrers, and staying on top of proactive security monitoring.

This is where SiteLock comes in. The company offers a comprehensive suite of tools designed to protect against CSRF and other security threats:

• Automated Website Scanning: SiteLock’s scanning service detects vulnerabilities, including CSRF, by simulating hacker behavior. If a vulnerability is detected, site owners are promptly notified, enabling them to take immediate action.
• Web Application Firewall (WAF): SiteLock’s WAF filters out malicious traffic by blocking forged requests and referencing known attack patterns. It lets only legitimate traffic reach your site, significantly reducing the risk of CSRF attacks.

Learn more about our website hardening solutions and address custom vulnerabilities in your site’s configuration, further strengthening your web application security. With SiteLock’s tools in place, you can be confident that your website is protected from CSRF threats, backed by a strong security setup that keeps your users safe.