Browser Terms Explained: Cross-site request forgery (CSRF)

If you're an avid internet user, you may have heard of the term "Cross-site request forgery" or "CSRF". Perhaps you've even encountered it on your favorite website or application. In this article, we'll dive deep into the world of CSRF, what it is, how it works, and most importantly, how to prevent it.

Understanding Cross-site Request Forgery (CSRF)

Cross-site request forgery, also known as XSRF or CSRF, is a type of cyber attack that exploits the trust relationship between an authenticated user and a website. In essence, it is a method of tricking a victim into unwittingly making a request on a website that they are currently logged in to.

What is Cross-site Request Forgery?

At its core, CSRF is a technique that forces an authenticated user to execute unwanted actions on a website without their knowledge or consent. This is done by exploiting the fact that most web browsers include cookies with every request that is sent to a website. These cookies are used to keep track of a user's identity, authenticate them, and ensure that they have the appropriate permissions to carry out certain actions.

When an authenticated user visits a website, their browser automatically sends the appropriate cookies with every request that it makes to that site. This allows the user to fully interact with the website, without having to re-authenticate every time they perform an action. Unfortunately, this convenience also creates a vulnerability. If an attacker can trick the victim into visiting a website that they control, they can force the victim's browser to send requests to the targeted website, using the victim's own authentication credentials.

How CSRF Attacks Work

Now that we know what CSRF is, let's take a closer look at how these attacks actually work. In a typical CSRF attack, the attacker designs a webpage or other resource that contains one or more requests to the targeted website. These requests are designed to carry out some sort of unwanted action, such as changing the user's password, creating a new account, or making a purchase.

The attacker then lures the victim into visiting the malicious website, perhaps by sending them a phishing email, or by creating a fake social media post. When the victim visits the website, their browser sends the cookies along with the request, and the targeted website mistakenly believes that the user has made a legitimate request.

Real-world Examples of CSRF Attacks

CSRF attacks can take many forms, and there have been several high-profile examples of such attacks in recent years. One such example occurred in 2018, when a group of hackers used a CSRF attack to change the DNS settings of several large websites, including Google and Amazon. By redirecting users to a fake website, the attackers were able to steal cryptocurrency from unsuspecting victims.

Another example occurred in 2021, when a researcher discovered vulnerabilities in several popular VPN applications. Using a CSRF attack, the researcher was able to bypass the VPN's security measures and access sensitive user data.

The Impact of CSRF Attacks

CSRF attacks can have a significant impact on both users and the websites they interact with. In this section, we'll take a closer look at the potential security risks of CSRF attacks, as well as the consequences for vulnerable web applications.

Security Risks for Users

One of the primary risks of CSRF attacks is that unsuspecting users may inadvertently carry out unwanted actions on websites that they trust. This could lead to a loss of privacy, financial loss, or other undesirable outcomes. For example, an attacker could use a CSRF attack to transfer money out of a victim's bank account, or to access personal email or social media accounts.

Consequences for Web Applications

Web applications that are vulnerable to CSRF attacks can suffer significant consequences. In addition to potential financial losses resulting from fraudulent transactions, a successful CSRF attack can also damage the reputation of the targeted website. Users who experience unexpected behavior, such as unauthorized purchases or account access, may be less likely to trust the website in the future. This could lead to decreased traffic, loss of revenue, and overall negative impact on the company's bottom line.

Financial and Reputational Damage

Aside from the direct financial and reputational damage caused by successful CSRF attacks, there may also be indirect costs associated with mitigating those attacks. For example, a company may need to allocate significant resources towards patching vulnerabilities, improving security measures, or conducting post-attack investigations.

Common CSRF Vulnerabilities

Now that we understand the potential impact of CSRF attacks, let's take a closer look at some of the most common vulnerabilities that can leave websites vulnerable to such attacks.

Inadequate Session Management

One of the most common vulnerabilities that can lead to CSRF attacks is inadequate session management. This can include using predictable session tokens, failing to enforce strict session timeouts, or allowing multiple sessions to be active at once. By exploiting these vulnerabilities, attackers can brute-force their way into a user's authenticated session, and carry out unwanted actions using the victim's own session credentials.

Insufficient Token Validation

Another common vulnerability that can lead to CSRF attacks is insufficient token validation. Many websites rely on tokens to authenticate user requests and prevent unauthorized access. Unfortunately, if these tokens are improperly validated, they can be easily forged by attackers. This can allow an attacker to bypass authentication and carry out unauthorized actions on behalf of the user.

Unprotected Web Services

Finally, unprotected web services can also leave websites vulnerable to CSRF attacks. If a website allows third-party services to make requests on behalf of users, those services can be potentially exploited by attackers. This can include mechanisms such as APIs, cross-domain requests, or JSONP callbacks.

Preventing and Mitigating CSRF Attacks

Now that we know some of the most common vulnerabilities that can lead to CSRF attacks, let's take a closer look at some of the most effective ways to prevent and mitigate these attacks.

Implementing CSRF Tokens

Perhaps the most effective way to prevent CSRF attacks is to use CSRF tokens. These tokens are unique, unpredictable values that are included in every request that a user makes to a web application. They are typically generated by the server and included as hidden form fields or as custom HTTP headers. When a user submits a request, the server validates the token to ensure that the request is legitimate. If the token is missing or invalid, the server rejects the request.

Using SameSite Cookies

A newer approach to CSRF protection involves the use of SameSite cookies. SameSite cookies are a special type of cookie that is designed to prevent cross-origin resource sharing. When a user visits a website, their browser sends SameSite cookies along with the request. If the cookie includes a SameSite attribute, the browser will only send the cookie for same-site requests. This can prevent CSRF attacks by ensuring that cookies are not sent to malicious sites.

Applying Content Security Policy (CSP)

Finally, applying a Content Security Policy (CSP) can help to prevent CSRF attacks by restricting the types of requests that a webpage is allowed to make. A CSP is a set of rules that specify which resources a webpage is allowed to load, and where those resources can come from. If a webpage attempts to load resources from a domain that is not explicitly allowed by the CSP, the browser will block those requests. This can prevent malicious scripts from executing on the user's computer and carrying out unwanted actions.

Conclusion

CSRF attacks can pose a significant threat to both users and web applications. By exploiting the trust relationship between a user and a website, attackers can carry out unwanted actions using the victim's own authentication credentials. Fortunately, there are several effective ways to prevent and mitigate these attacks, including the use of CSRF tokens, SameSite cookies, and Content Security Policies.