Cross-Site Request Forgery (CSRF)

Anton Ioffe - October 7th 2023 - 16 minutes read

With the ever-developing digital landscape, ensuring robust security on your applications becomes not merely an option but an outright necessity. Among the vulnerabilities that can plague your applications, Cross-Site Request Forgery (CSRF) stands out as an insidious threat that every developer needs to understand deeply. Our comprehensive article, "JavaScript and CSRF: Insight, Impact, and Fortification Strategies in Modern Web Development," explores this high-stakes topic in an organized and engaging way, guaranteeing in-depth knowledge and practical guidance for experienced developers.

We start with decoding CSRF, unfolding its potential risks and relevance in contemporary JavaScript-driven applications. With an intimate understanding of CSRF, we navigate through its anatomy, revealing attack techniques and common aids to these exploits. As we delve further, we disambiguate CSRF from similar attack forms: XSS and phishing, allowing you to grasp the distinct signature of such attacks.

Beyond understanding CSRF, we venture into combat strategies, dissecting diverse defence mechanisms—particularly CSRF tokens, while apprising you of the implications of compromised tokens. Ultimately, we piece together a comprehensive guide on fortifying JavaScript applications against CSRF attacks, tying the entire discourse into actionable steps. From detection to resolution, simple coding tactics to grand security strategies, this article is intended to be your road map to CSRF-resistant web development.

Decoding Cross-Site Request Forgery (CSRF)

Cross-Site Request Forgery (CSRF) represents one of the salient web application vulnerabilities today, predominantly due to the potential high-impact risks it presents to the integrity and confidentiality of user data. In essence, this attack type tricks the victim into submitting a malicious request, masked as legitimate, thereby conducting unwanted actions in a web application they are authenticated in.

As developers and programmers working with JavaScript and modern web development landscapes, an understanding of CSRF can be viewed as intrinsic to the overall web security protocol awareness. Especially since it manipulates the inherent trust that a web site has with a user's browser, causing potential data breaches and unauthorized activities.

The imminent danger of CSRF lies in its virtually silent operation. Implementing its vicious cycle without the need for direct user interaction, essentially cementing its status as a high-threat security flaw. Security attributes, such as cookies that are automatically attached to requests by default, are exploited by CSRF, bypassing standard provisions made for user authenticity.

The impact of CSRF on a web application can range from creating unwanted user actions to potentially dangerous data manipulation, including altering email addresses and password changes, content tampering, and in severe cases, the application of financial transactions without the user's consent. The range of these actions underlines the cataclysmic consequences that could result from CSRF attacks.

It's worth noting that despite not being a new type of attack, CSRF consistently proves to be challenging due to modern Web complexity and the various attack vectors that need to be protected. Moreover, unlike other types of attacks, CSRF does not target vulnerabilities in the application's code but takes advantage of the ways the web operates.

A related query that comes to mind: "Isn't the Same-Origin Policy (SOP) designed to segregate scripts to their origins, thereby protecting against CSRF attacks?" Here, we glimpse CSRF's prowess in circumventing security measures. It exploits the fact that browser requests automatically include all credentials such as session cookies, IP addresses, and other authentication tokens. So while SOP does prevent the attacker from reading the response of the cross-site request, it does not prevent the request from taking place.

JavaScript's pivotal role in modern web development brings the CSRF complexity to light in a broader sense. As increased client-side rendering and Single Page Applications (SPAs) take preference, issues revolving XMLHttpRequest or Fetch API requests, saved tokens, and other JavaScript-related vulnerabilities rise to the fore, creating an even more pressing need for comprehensive CSRF security provisions in web development.

Reflect on how one might inadvertently allow for CSRF vulnerabilities in your current projects. What avenues of your applications might be most susceptible, and how could potential breaches impact your users? The relevance of these questions underlines that understanding CSRF plays a critical component in maintaining robust, secure web applications.

The Anatomy of CSRF Attacks

Cross-Site Request Forgery, commonly referred to as CSRF (pronounced 'sea-surf') is a type of exploit where unauthorized commands are transmitted from a user that the website trusts. While inherently devious, understanding its inner workings can empower developers to construct robust defense mechanisms against such threats.

Part Uno: CSRF's Modus Operandi

The foundation of a CSRF attack lies in exploiting the trust an application has for a validated user. Let's envisage a social media platform where users can post status updates. A legitimate update operation would look like this:

function updateStatus(token, newStatus) {
    // [HTTP POST method is used to update status]('/updateStatus', {
        status: newStatus, 
        token: token

Here, we're assuming that the server has session cookies enabled and the user is already logged in. The token is a kind of security measure provided by the server to authenticate the request.

In a CSRF exploit, a malicious site could trick the user into executing an update status operation with their own nefarious content. This counterfeit request would be identical to a genuine request, bar the status content. Once the user accesses the malicious page, a JS code would execute in the background, similar to:

// Malicious JS on offender's site
function csrfAttack() {
    // HTTP POST method is used to invoke an action in the user's session'', {
        status: 'I love CSRF!', 
        token: csrfToken

The user isn't asked for permission, nor are they notified of this update — it's all part of the devious CSRF mechanism. Unless the user manually checks their statuses, they'll be clueless about the unauthorized changes.

Cooking Up Trouble: Role of Cookies

Cookies play an indispensable role in CSRF attacks. A user's authenticated session is typically kept alive using cookies. When an attack occurs, the victim’s browser automatically includes all cookies for the targeted domain in the malicious request. If the user is authenticated and their session ID is still valid, the request will be endorsed at the server-side with no immediate suspicion.

HTTP Methods in CSRF

While most documented CSRF exploits exploit the POST method, GET methods can be equally dangerous if not handled correctly. It's not uncommon to see developers using GET methods for state-changing operations out of convenience or ignorance, playing right into the hands of attackers. You must remember that safer HTTP methods like GET should never be used for operations modifying the resource state.

Friend or Foe: Identifying CSRF Exploits

Herein lies the dilemma for applications. CSRF requests are essentially indistinguishable from legitimate ones as they come with all necessary valid credentials - cookies, IPs, sessions, you name it. This makes detecting CSRF attacks a tricky business.

To round off this section, here's a thought-provoking question for you - given CSRF attacks' chameleon nature, how would you propose detecting such attacks in real-time?

In subsequent sections, we will delve into CSRF protection patterns and best practices, reversing the perilous implications of this dexterous exploit.

Contrasting CSRF: Disambiguating from Phishing and XSS Attacks

Understanding common web application vulnerabilities is central to creating secure code. As developers, we often encounter the words Cross-Site Request Forgery (CSRF), Cross-Site Scripting (XSS), and Phishing. However, while they might seem similar on the surface, they each harbor certain unique characteristics and technical execution nuances. In this section, we'll differentiate CSRF attacks from XSS attacks and phishing to enhance your proficiency in detecting and avoiding these security pitfalls.

Cross-Site Request Forgery (CSRF):

At its core, CSRF is an attack vector that tricks the victim into performing actions they do not intend to do on a web application in which they're authenticated. It occurs when a malicious website, email, or program causes a user's web browser to perform an unwanted action on a trusted site.

Code Example: A CSRF attack can trick the victim into performing an unauthorized withdrawal operation on a banking site if the victim is authenticated.

const csrfLink = document.createElement('a');
csrfLink.setAttribute('href', '');
csrfLink.innerHTML = 'Click here to see kittens!';

In this JavaScript example, the malicious link could be appended to a webpage. An unsuspecting user, believing they are clicking a link to see kittens, could unknowingly instruct their bank to transfer funds to a malicious user's account.

Cross-Site Scripting (XSS):

Unlike CSRF attacks that focus on authenticated requests, XSS assaults revolve around injecting malicious scripts into sites trusted by end users. The goal is to dupe the user's browser into executing the script, providing the attacker access to sensitive information or control over user interactions.

Code Example: Let's simulate an XSS attack where a malicious script is embedded in a user's comment on a post.

const userComment = `<img src='' onerror='stealCookies()'>`

In this case, the script within the user's comment would execute in other users' browsers when the post is viewed, potentially stealing their cookies or performing other unintended actions.


Phishing is less about technical exploits and more about deception. It employs social engineering mechanisms to acquire users' sensitive information, like usernames and passwords. It's often carried out through disguised rogue emails or websites that closely resemble legitimate entities.

Code Example: A user could receive a deceptive email appearing to come from their bank, asking them to log in and verify their account details. The link provided, however, redirects them to a fake version of the bank's website, designed to steal login credentials.

const phishingEmail = `
    <p>We've noticed suspicious activity on your account. Please click the link below to verify your details:</p>
    <a href="">Verify your account</a>
sendEmail('', 'Important: Verify Your Account', phishingEmail);

This JavaScript example hammers home the fact that phishing attacks are savvy, manipulative and can easily fool unsuspecting users into providing sensitive information.


While CSRF, XSS, and phishing might share similarities in the sense that they exploit trust and trick users into performing unwanted actions, they are fundamentally different in their execution. CSRF capitalizes on a user's authenticated state, XSS leverages the user's trust in a legitimate website, and phishing relies chiefly on user deception. These differences are key for developers as they craft solutions to identify and thwart such attacks.

Have you ever fallen prey to a CSRF, XSS, or phishing attack in your development career? How have these experiences shaped your approach to writing secure code? Would detecting a CSRF attack be easier now that you understand the difference between it and XSS and phishing scenarios? These are questions worth pondering as you navigate the intricacies of web application security.

Deconstructing CSRF: Detection and Evaluation

Cross-Site Request Forgery, commonly known as CSRF, is a pervasive threat in the modern web development landscape. This section seeks to shed light on the identification and evaluation process of CSRF vulnerabilities in your JavaScript applications.

One of the most common oversights is failing to validate and sanitize user inputs and payloads. Many developers obfuscate the underlying application logic and focus too much on user experience and visual output, thereby inadvertently overlooking input validation.

Let's explore the specific mistakes one might make in the detection phase of a CSRF attack, as well as their correct counterparts.

Consider this insecure HTTP request handling:'/api/expense', function(req, res) {
    let expenseId = req.body.expenseId;
    let userId = req.session.userId;

    Expense.update({approved: true}, {where: {id: expenseId}});

The above endpoint updates the 'approved' flag of an expense entry without validating if the user has appropriate permissions to perform this action. An attacker could manipulate the expenseId and compromise any expense entry.

The correct approach would be to validate the user’s action, ensuring that the userId in the session has the right to alter the expenseId they are sending.'/api/expense', function(req, res) {
    let expenseId = req.body.expenseId;
    let userId = req.session.userId;

    Expense.findOne({where: {id: expenseId, userId: userId}}).then(expense => {
        if(expense) {
            Expense.update({approved: true}, {where: {id: expenseId, userId: userId}});
        } else {
            // Handle error - the user does not have necessary rights or the expense does not exist

The above code first validates whether the expense associated with the expenseId also belongs to the userId in the session, adding an extra layer of security to prevent CSRF attacks.

In terms of evaluation, the severity of a CSRF vulnerability is often directly proportional to the permissions that the coerced transaction holds. So, a CSRF vulnerability that enables an attacker to modify an email address can potentially be less detrimental than one that allows arbitrary account withdrawals.

As developers, it's vital to question:

  • Are all actions performed by authenticated and privileged users validated for permission consistency?
  • Are there sensitive actions in the application, where CSRF attacks would have significant consequences?
  • Are there user interfaces and experience flows that may make CSRF attacks easier or more likely to succeed?

Bear in mind that while CSRF vulnerabilities are often associated with malicious third-party entities, there's a viable risk from internal threats. Therefore, it's crucial that internal applications are just as thoroughly veted for CSRF vulnerabilities.

In summary, detecting and evaluating CSRF vulnerabilities requires comprehensive input validation, precise permission checks, and awareness of potential damages. Successful navigation of these considerations will result in much more secure JavaScript applications.

CSRF Defense Mechanisms: Tokenization and Beyond

The primary and most frequently employed method to defend against CSRF attacks is through the use of CSRF Tokens. This technique is based on synchronizing a secret token between the client and server applications. Each time a user makes a request, a unique token is generated, associated with that user session, and embedded within the form. The server then validates this token and only proceeds with the request if it matches the stored token.

Here is an example of this technique implemented in JavaScript:

let csrfToken;

function generateToken() {
    // Generate a new token using a secure method
    csrfToken = window.crypto.subtle.generateKey(
            name: 'HMAC',
            hash: {name: 'SHA-256'}
        ['sign', 'verify']

While dealing with numerous form requests, a method for embedding the CSRF token in every request can be defined, as follows:

function embedTokenInRequest(form) {
    let hiddenField = document.createElement('input');
    hiddenField.setAttribute('type', 'hidden');
    hiddenField.setAttribute('name', 'csrfToken');
    hiddenField.setAttribute('value', csrfToken);

In these examples, generateToken() generates a distinct token each time a user initiates a new session. In comparison, the embedTokenInRequest() function adds these tokens as hidden fields to each outgoing form request.

However, CSRF tokens are not a silver bullet solution and should be complemented with other techniques. One such method utilizes the SameSite cookie attribute which, if set to Strict or Lax, will only send the cookie if the request came from the same site i.e., the same origin. Consequently, this will disallow any potential CSRF attacker from sending preformed requests with the user's cookie data. This attribute can be set in the Set-Cookie header of an HTTP response, like so:

document.cookie = 'sessionId=1234; Secure; SameSite=Strict';

In this example, setting the SameSite attribute to Strict ensures the cookie is only included in requests sent from the same site. Note that the Secure attribute is also set, making sure the cookie is only sent over secure (HTTPS) connections.

However, be aware that the SameSite attribute is not supported in all browsers. Therefore, while it's an excellent security improvement, it should not be your only line of defense against CSRF attacks.

Another important measure is to enforce the principle of least privilege, providing each user with the minimum privileges necessary to perform their tasks. This would limit the damage an attacker can cause even if they manage to launch a successful CSRF attack.

These CSRF prevention techniques, when used together, can significantly bolster the security of your web applications. Note that no single approach is fully foolproof, and layering different methods is always the best practice in cybersecurity.

So now, ask yourself - how secure is your JavaScript code from CSRF attacks, and what measures can you take to better protect your users and your application?

When Protection Fails: Implications of Stolen CSRF Tokens

Cross-Site Request Forgery (CSRF) tokens are crucial components in safeguarding applications from CSRF attacks. Despite best efforts, there are instances when these tokens, the very core of CSRF protection, might be stolen or compromised, leading to a breach of the security fort. At a high level, CSRF tokens ensure that every action initiated is genuinely done by the authenticated user, variably stamping out any chances of malicious effects of forced actions. However, if an attacker gets hold of these tokens, the projected layer of security crumbles, potentially plunging the application and its users into an array of security turmoil.

The impacts of stolen CSRF tokens can be far-reaching, depending on the extent of access these tokens facilitate. One immediate implication is the potential for unauthorized actions being performed on behalf of the user. With a stolen CSRF token, an attacker can impersonate the victim and execute actions that may lead to disclosure of sensitive data, modification of user data, or even deletion of user accounts.

Another possible outcome is the escalation of privileges. A skilled attacker may be able to elevate their access levels within an application, gaining unwarranted access to resources and performing operations that ought to be restricted. This could lead to an extensive data breach, a scenario dreaded by both companies and users alike.

In more severe cases, stolen CSRF tokens can grant an attacker the ultimate power of exploiting administrative functions. This can spell disaster for any web application, as it allows the attacker to manipulate the system in detrimental ways, including changing security settings, managing user privileges, and conducting potentially ruining business operations.

Let's take a quick look at these concepts in code for better clarity. Let's imagine an anonymous function acquiring a CSRF token.

(function getCsrfToken(){
    let url = '/getCsrfToken';
    .then(response => response.json())
    .then(data => {
        console.log('Token: ', data.token);

In this example, obtaining the CSRF token is as simple as fetching it from a designated URL. An attacker who successfully injects this code snippet can steal CSRF tokens and use them in subsequent malicious requests, potentially causing grave damage.

It's essential to reiterate the importance of additional security measures protecting CSRF tokens. Measures may include using secure and HttpOnly cookies to store tokens safely, employing effective domain and path scopes for cookies, and using secure transport for sending tokens. Regular regeneration of tokens can also help limit the potency of any stolen token. The use of these protective practices offers multiple layers of security and moves us away from overreliance on the robustness of CSRF tokens.

Can you think of any other potential implications of stolen CSRF tokens? How would these implications change if different types of CSRF tokens were used and stolen?

JavaScript in Action: Building CSRF-resistant Web Applications

JavaScript developers, let's jump right into the heart of the matter: building CSRF-resistant applications. Our weapon of choice is a blend of established development strategies, secure coding techniques, and regular security tests. Shall we dive in?

1. Embrace Development Strategies

Building CSRF-resistant JavaScript applications requires much more than just adhering to coding conventions; it involves walking through an entirely evolved landscape. We're talking about using the latest libraries and frameworks, understanding emerging security threats, and employing preventive measures.

Let's take code reviews, for instance. They have proven to offer an eagle's eye view into potential security loopholes that could be exploited by attackers. Have you ever considered integrating peer reviews or pair programming into your development cycle, to further fortify your application defense? What steps have you taken to enforce coding guidelines within your team? The implementation of linters can be a pivotal step towards this initiative.

// Incorporating ESLint as a linter in your JS code
module.exports = {
  'env': {
    'browser': true,
    'es2021': true
  'extends': 'eslint:recommended',
  'parserOptions': {
    'ecmaVersion': 12
  'rules': {
    'semi': [

2. Secure Coding Techniques

Secure coding techniques embody several aspects of JavaScript development:

  • Use of HTTPS: Why should you use HTTPS instead of HTTP? It ensures data transmitted between server and client is encrypted, making it hard for intruders to intercept the session. An integral part of creating CSRF-resistant applications, don't you agree?

  • HttpOnly Cookies: By enabling the HttpOnly attribute on cookies, you prevent JavaScript from accessing them, thereby safeguarding against CSRF attacks. Have you realized the power and simplicity of this technique?

  • Valid Sessions: Ensuring user sessions are still valid, with automatic expirations after a certain period of inactivity or explicit logouts, is a strategy worth considering.

// Ensuring HttpOnly Cookies in JavaScript
document.cookie = "username=JohnDoe; expires=Thu, 18 Dec 2023 12:00:00 UTC; path=/; HttpOnly";

3. Regular Security Testing

Along with development strategies and secure coding techniques, regular security testing forms the third pillar of our CSRF-resistant fort:

  • Penetration Testing: This involves ethical hackers trying to breach security to discover vulnerabilities, including CSRF. Tools like OWASP ZAP can automate this process. Have you looked into incorporating such tools in your workflow yet?

  • Security Scanning: Security scanners, like Snyk or SonarQube, can identify common security failures in code. Automating these scans as part of your CI/CD pipeline can be an efficient approach.

  • Automated Unit Testing: This ensures every part of your application is CSRF-resistant and functions as anticipated. Which tools or practices are you currently using for this?

The strategies discussed are not exhaustive but provide a robust starting point. Building security against CSRF threats is an ongoing endeavor, with regular updates and vigilance serving as your best allies in fortifying your application's defense. Are you ready for the battle against CSRF?


The article "JavaScript and CSRF: Insight, Impact, and Fortification Strategies in Modern Web Development" provides an in-depth exploration of Cross-Site Request Forgery (CSRF) and its implications in modern web development. It highlights the importance of understanding CSRF as a critical component of web security and discusses its relevance in JavaScript-driven applications. The article covers the anatomy of CSRF attacks, disambiguates CSRF from other attack forms such as XSS and phishing, and offers strategies for fortifying JavaScript applications against CSRF attacks.

Key takeaways from the article include the understanding that CSRF attacks exploit the trust between a web application and a user's browser, the potential silent operation of CSRF attacks without direct user interaction, and the range of actions that can result from CSRF attacks, including unauthorized data manipulation and financial transactions. The article also emphasizes the complexity of CSRF in modern web development due to increased client-side rendering and the importance of comprehensive CSRF security provisions.

A challenging technical task for the reader could be to analyze their current projects and identify potential CSRF vulnerabilities. They could reflect on which parts of their applications might be most susceptible to CSRF attacks and consider the impact of potential breaches on their users. This task encourages the reader to actively assess the security of their JavaScript code and take steps to better protect their applications and users from CSRF attacks.

Don't Get Left Behind:
The Top 5 Career-Ending Mistakes Software Developers Make
FREE Cheat Sheet for Software Developers