Cross-site scripting (XSS) and cross-site request forgery (CSRF) are among the most common and well-known web security vulnerabilities. Though they often get mentioned together and may seem similar because both have “cross-site” in the name, they exploit very different aspects of web applications and browsers. Understanding the distinction is essential for developers, testers, and security teams aiming to protect users and sensitive data.

Overview of XSS (cross-site scripting)

What XSS targets

XSS attacks target the end user by injecting malicious scripts into trusted websites. The attacker’s goal is to execute JavaScript in the context of the victim’s browser session. These scripts can steal cookies, hijack sessions, deface pages, or redirect users to malicious websites.

How XSS attacks are delivered

XSS payloads are typically delivered via input fields, query parameters, or other entry points that are reflected or stored by the application without proper sanitization. The most common types are:

• Reflected XSS: Payload is submitted by the user and directly reflected in the server response.
• Stored XSS: Payload is saved on the server and triggered when another user views the affected content.
• DOM-based XSS: Payload manipulation occurs entirely in the browser via JavaScript.

Overview of CSRF (cross-site request forgery)

What CSRF targets

CSRF exploits the trust a web application has in a user’s browser. It forces authenticated users to perform unwanted actions on a site where they are logged in, such as changing account settings or initiating transactions.

How CSRF exploits browser trust

When a user is authenticated to a web application, their browser automatically includes session cookies in any request to that domain. CSRF takes advantage of this by tricking the user into submitting a forged request—for example, via an embedded image or form on a malicious site—without their knowledge or consent.

Key differences between XSS and CSRF

Attack mechanism

• XSS involves injecting malicious scripts that run in the user’s browser. These scripts exploit the trust a user has in a specific website, enabling the attacker to execute JavaScript in the context of that site.
• CSRF involves sending unauthorized requests from the browser to a trusted application. The attacker doesn’t need to inject code but instead tricks the browser into making a request that the server assumes is legitimate.

Security impact

• XSS allows attackers to directly interact with the browser’s DOM and session data, potentially stealing tokens, manipulating page content, logging keystrokes, or escalating access through other means.
• CSRF causes users to unintentionally perform actions like form submissions, data updates, or transactions. The attacker leverages existing credentials and sessions without needing access to those credentials themselves.

Defense strategies

• XSS mitigation involves a multi-layered approach, including input sanitization (validating and cleaning user input), output encoding (safely rendering content in HTML or JavaScript), and applying Content Security Policy (CSP) headers to restrict script execution sources.
• CSRF defense requires verifying that each state-changing request comes from an authorized source. Techniques include embedding CSRF tokens in forms, setting cookies with the SameSite attribute to limit cross-origin usage, and requiring users to re-authenticate for critical operations. These measures ensure that requests can’t be forged without user intent.

Real-world examples and use cases

XSS in comment fields

An attacker posts a comment containing a script tag on a blog. When another user reads the comment, the script runs in their browser, stealing session cookies or redirecting them to a malicious page.

CSRF in form submissions

A logged-in user visits a malicious site that secretly submits a form to change their email address on a banking site. The browser includes valid session cookies, and the change is processed without user awareness.

Which is more dangerous? XSS vs CSRF

Both vulnerabilities are serious but differ in scope. XSS is generally considered more dangerous because it gives attackers direct access to the client-side execution environment, allowing for a wide range of malicious actions. CSRF depends on existing authenticated sessions and typically requires some form of user interaction. However, in combination with other issues (like weak authentication), CSRF can still have serious consequences.

Detecting XSS and CSRF vulnerabilities with DAST

DAST is uniquely positioned to detect XSS and CSRF vulnerabilities because it tests applications in their running state, focusing on real-world exploitability rather than theoretical issues. For XSS, DAST tools actively inject a range of payloads and monitor how the application processes and outputs user input—pinpointing places where malicious scripts can be executed in the browser. For CSRF, modern DAST solutions assess the presence and implementation of security controls such as CSRF tokens and SameSite cookie attributes to identify flaws that could allow unauthorized requests to slip through.

A DAST-first approach ensures teams are prioritizing genuine, exploitable risks. By simulating attacker behavior and proving vulnerabilities with actionable evidence, Invicti’s DAST platform cuts through the noise that plagues static testing tools. This not only reduces false positives but also accelerates remediation, allowing security and development teams to focus their efforts where they matter most. Incorporating DAST as a foundational layer of application security provides reliable, continuous protection against pervasive threats like XSS and CSRF—keeping security aligned with the pace of modern development.