CSRF vs. XSS: Key Differences and 5 Ways to Protect Your Website

What Is CSRF? 

Cross-site request forgery (CSRF) is a type of malicious exploit where unauthorized commands are transmitted from a user that the web application trusts. It leverages the authenticated state of a user to push unwanted actions without their consent or knowledge. The attack exploits the victim's browser, provided they are already authenticated, rendering the attack invisible to conventional user interfaces or firewalls.

CSRF attacks are dangerous because they occur without user awareness. When an attacker successfully crafts the payload and tricks the user into executing it, harmful transactions can occur under the guise of legitimate user action. This can lead to unauthorized fund transfers, password changes, or data manipulation, as the server cannot distinguish between legitimate and forged user requests.

What Is XSS? 

Cross-site scripting (XSS) exploits vulnerabilities within web applications to inject malicious scripts into webpages viewed by other users. Attackers leverage these scripts to execute arbitrary commands in another user's browser, effectively hijacking their session to steal data or impersonate victim actions. XSS attacks generally target the client-side and manipulate the user's interaction with the web application.

XSS attacks capitalize on insufficient input validation processes of web applications, allowing the injection of executable scripts. These attacks can be classified as stored, reflected, or DOM-based, each implying different mechanisms and dangers. The goal is to exploit untrusted scripts to breach user privacy and compromise web application's integrity and security.

This is part of a series of articles about application security.

How Does CSRF Work? 

CSRF works by exploiting the trust that a web application has in a user’s browser session. Attackers craft malicious requests that seem legitimate to the server but are initiated without the user's consent. The attack typically follows these steps:

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1. Victim authentication: The victim logs into a trusted web application, creating a session with an active authentication token, often stored in cookies.
2. Crafting a malicious request: The attacker generates a request designed to perform an unauthorized action on behalf of the user, such as transferring funds or changing account details. This request aligns with the format the application expects for legitimate user actions.
3. Tricking the victim: The attacker embeds the malicious request in a medium the victim might interact with, such as a phishing email, a compromised website, or even an embedded image or form.
4. Executing the request: When the victim unknowingly interacts with the malicious payload, their browser sends the request to the trusted server, including the valid authentication token stored in the session. The server processes the request, assuming it originated from the authenticated user.

The main vulnerability is the server’s inability to differentiate between a legitimate user-initiated request and a malicious request crafted by an attacker. Since the browser automatically includes session credentials (like cookies) with requests to the trusted site, the attack bypasses authentication checks.

How Does XSS Work? 

XSS attacks manipulate web applications to deliver malicious scripts to end users. These scripts execute in the victim's browser, exploiting the application's failure to sanitize or validate user-supplied input. Here’s how an XSS attack generally unfolds:

1. Identifying a vulnerability: The attacker identifies an input field or an entry point where user-provided data is incorporated into a web page’s output without proper sanitization. This could be a comment section, search bar, or URL parameter.
2. Injecting malicious scripts: The attacker crafts a payload containing malicious JavaScript code and submits it through the vulnerable input field. Depending on the type of XSS, the payload may be stored (persisting in the application), reflected (immediately executed in the victim’s browser), or DOM-based (executed dynamically through client-side scripts).
3. Execution in the victim's browser: When the victim interacts with the compromised webpage, the malicious script is executed in their browser context. Since the script is running as part of the legitimate webpage, it can access sensitive data, such as cookies, session tokens, or browser storage.
4. Exfiltration or manipulation: The script may steal the victim’s session information, redirect the user to a malicious site, modify page content, or impersonate the user’s actions.

The success of XSS relies on the victim's trust in the website and the browser’s execution of the malicious script as though it were part of the legitimate page. Preventing XSS requires rigorous input validation, proper output encoding, and secure coding practices to ensure user input cannot introduce malicious behavior.

Tzvika Shneider

CEO, Pynt

Tzvika Shneider is a 20-year software security industry leader with a robust background in product and software management.

Tips from the expert

In my experience, here are tips that can help you better mitigate and address CSRF and XSS vulnerabilities:
• Segment application functionality with different subdomains: Isolate sensitive functionalities (e.g., transactions, account management) on separate subdomains. This prevents session cookies from being shared across subdomains, limiting the attack surface for CSRF and XSS.
• Implement double-submit cookies for CSRF mitigation:: Use double-submit cookie patterns where the CSRF token is stored both as a cookie and a form field value. The server then verifies that both values match. This approach adds redundancy and works well alongside SameSite cookie attributes.
• Leverage subresource integrity (SRI) for external scripts:For external scripts, use SRI to ensure the fetched resource hasn’t been tampered with. SRI hashes validate that the script content matches its expected signature, preventing malicious script injection.
• Apply rate-limiting to reduce CSRF and XSS exploitation: Restrict the frequency of state-changing actions such as password resets, fund transfers, or comment submissions. Rate-limiting makes it harder for attackers to automate CSRF or XSS exploitation at scale.
• Use sandboxed iframes for embedding third-party content: When embedding third-party content or widgets, use sandbox attributes to restrict script execution and block access to sensitive application data. This minimizes exposure to malicious scripts originating from external sources.

CSRF vs. XSS: The Key Differences 

1. Attack Mechanism

CSRF relies on exploiting the authenticated sessions of users by deceiving them into executing harmful requests, usually via crafted forms or links. Attackers use social engineering tricks to bypass the authentication process, implicating the user directly in the transaction. Unlike XSS, which inserts scripts into web applications to affect other users, CSRF vectors target actions without script-based payloads, focusing purely on mimicking legitimate requests.

XSS inserts malicious scripts within web pages that execute in the context of the viewing user. This script-based attack manipulates content across multiple sessions and often impacts multiple users relying on shared access points. XSS works predominantly by leveraging weak input validation to infiltrate user browsers, executing codes that compromise personal and application data security.

2. Primary Focus of Attack

CSRF targets the transmission layer by mimicking or fooling authenticated user actions to achieve harmful outcomes. The attack's core leverage is against the user’s authenticated state, focusing on the user-server interaction layer. Its prime objective is to manipulate transactional data within an authenticated session, altering data, and state unbeknownst to the victim.

XSS focuses more on the client layer, affecting how users interact with web applications through script execution. XSS can lead to data theft, session hijacking, and defacement of content. This attack strategy impacts the client's local script execution processes, affecting one or many users depending on the exposure scale of the system flaw.

3. Actor Involvement

In CSRF, the attack is client-oriented, with the victim playing an unknowing accomplice in the attack framework. The attacker remains concealed from direct interaction by crafting contexts which the user inadvertently activates. The attack is effective through exploiting trust relationships inherent between the browser and web application, taking control through this indirect execution pathway.

In XSS, the attacker actively interfaces with user input points or injects scripts directly into the web application infrastructure. The executed scripts directly compromise the user's browsing environment, often involving dynamic injection and execution tactics. Attackers manipulate users into pathways where scripts are run, giving them access to browser-level information secretly.

Related content: Read our guide to prompt injection

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Protecting Against CSRF and XSS Attacks 

Organizations should consider the following practices to ensure maximum protection against these types of attacks.

1. Using CSRF Tokens

To prevent CSRF attacks, web applications can deploy unique tokens signed to each user session. These tokens are validated during state-changing requests to ensure legitimacy. By embedding these tokens within forms and verifying them on request processing, servers can validate whether the request originated from an authenticated session, blocking unauthorized actions as attackers cannot easily replicate these dynamic tokens.

CSRF tokens are bound to the user's session, aligning with server-side tracking to ensure authenticity. The integration of these tokens into critical workflows ensures any interloping requests lacking matching credentials are automatically rejected.

2. SameSite Cookies

Implementing SameSite cookie attributes adds a layer of protection by controlling when cookies are sent with requests. By setting cookies to SameSite=Lax or SameSite=Strict, browsers limit cookies to first-party contexts, preventing them from being attached to cross-site requests. This reduces the surface area for CSRF attacks, since cookies are less likely to accompany malicious third party requests.

SameSite cookies provide mitigation through explicit control over the contextual conditions under which cookies might be accessed. By minimizing third-party cookie sharing, web applications considerably reduce vulnerability exposure to CSRF attempts while preserving session integrity with enforced access constraints.

3. Input Validation and Sanitization

For XSS prevention, rigorous input validation and output sanitization are critical. Incoming data should be validated against expected formats and output should be escaped or encoded to neutralize harmful scripts. By implementing allowlisting principles, applications can reduce the risk of injecting malicious code, ensuring any user-driven content is adequately screened before processing or display.

Developers must deploy an input sanitation framework to handle various inputs dynamically, leveraging encoding techniques to defang potential scripts. This prevents malicious content from being processed or presented to other users, protecting client-side environments from script intrusions while maintaining functionality and usability.

4. Define a Content Security Policy (CSP)

Creating and enforcing a strict content security policy (CSP) is vital for mitigating XSS risks. CSPs define trusted sources for executing scripts and acceptable content types, thus preventing unauthorized script execution. By outlining which resources can execute within a page, CSPs drastically reduce potential entry points for XSS attacks, reinforcing user protection at the browser level.

CSP implementations offer protection by establishing execution boundaries, blocking unauthorized scripts site-wide. As a systemic control measure, it fortifies defense lines not just against accidental script leaks but also inhibits refocusing attacks from compromised scripts.

5. Regular Security Testing

Conducting regular security assessments helps identify and resolve CSRF and XSS vulnerabilities. This includes automated tool scans and manual code audits, ensuring applications remain patched against known exploits. Regular testing aligns strategic security measures with evolving threat landscapes, validating defense mechanisms effectively against potential vulnerabilities.

Security testing further ensures compliance with all relevant security standards, providing assurance that protective strategies are effective. Through continuous evaluation and remediation efforts, organizations can shield themselves from breaches, keeping pace with emerging security challenges.

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