What Is Non-Persistent Cross-Site Scripting?


Larry Thompson

What Is Non-Persistent Cross-Site Scripting?

Non-persistent Cross-Site Scripting (XSS) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. It occurs when user input is not properly validated or sanitized before being displayed on a website.

Understanding Cross-Site Scripting

Cross-Site Scripting is a widespread vulnerability that can have severe consequences for websites and their users. In a typical XSS attack, an attacker injects malicious code, usually in the form of JavaScript, into a web page viewed by unsuspecting users. This code is then executed in the context of the victim’s browser, allowing the attacker to steal sensitive information, manipulate site content, or perform other malicious actions.

The Difference: Persistent vs. Non-Persistent XSS

There are two main types of XSS attacks: Persistent (or stored) XSS and Non-Persistent (or reflected) XSS. Persistent XSS occurs when the injected script is permanently stored on the Target server. This means that every time a user visits the affected page, they will be exposed to the malicious script.

Non-Persistent XSS, on the other hand, relies on tricking users into visiting a specially crafted URL that contains the injected script. The script is not permanently stored on the server but rather included in the URL parameters or form inputs. When the victim clicks on the manipulated link or submits a vulnerable form, their browser executes the injected script.

The Process of Non-Persistent XSS

  1. The attacker identifies a website that is vulnerable to non-persistent XSS.
  2. The attacker crafts a URL or prepares an input field with malicious code.
  3. The attacker convinces the victim to click on the manipulated link or submit a vulnerable form.
  4. The victim’s browser sends a request to the vulnerable website, including the malicious script in the URL parameters or form inputs.
  5. The server reflects the injected script back to the victim’s browser as part of the website’s response.
  6. The victim’s browser executes the script, allowing the attacker to perform various malicious actions.

Preventing Non-Persistent XSS Attacks

Protecting against non-persistent XSS attacks requires proper input validation and output encoding. Here are some best practices:

  • Input Validation: Validate and sanitize all user-supplied input to remove or escape any potentially dangerous characters. Use a combination of client-side and server-side validation techniques.
  • Output Encoding: Encode all user-generated content before displaying it on web pages.

    Use appropriate encoding functions such as HTML entity encoding or context-specific encoding (e.g., JavaScript encoding for inline scripts).

  • Content Security Policy (CSP): Implement a Content Security Policy that restricts which resources can be loaded on a website. This can help mitigate XSS attacks by blocking or limiting the execution of injected scripts.
  • Regular Security Audits: Regularly audit your website’s codebase for potential vulnerabilities, including XSS vulnerabilities. Use automated scanning tools and manual code reviews to identify and fix any issues.

The Importance of User Education

In addition to technical measures, educating users about the risks of clicking on suspicious links or submitting personal information on untrusted websites is crucial. Encourage users to be cautious and vigilant when interacting with online content and provide guidelines on how to identify and report potential security threats.


Non-persistent Cross-Site Scripting (XSS) is a serious security vulnerability that can have severe consequences for both websites and their users. By understanding the nature of XSS attacks and implementing proper security measures, developers can protect their applications from this type of threat. Remember, prevention is always better than trying to mitigate the damage caused by an XSS attack.

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