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[ Preventing XSS attacks ]

[ Preventing XSS attacks ] 

In the video it illustrates three version of an XSS attack: high level, detailed with the script tag, and detailed with no script tag, and then recommends resources for further learning. 
Cross-site scripting holes are web-application vulnerabilities which allow attackers to bypass client-side security mechanisms normally imposed on web content by modern browsers. By finding ways of injecting malicious scripts into web pages, an attacker can gain elevated access privileges to sensitive page-content, session cookies, and a variety of other information maintained by the browser on behalf of the user.

Cross-Site Scripting (XSS) attacks occur when:
  1. Data enters a Web application through an untrusted source, most frequently a web request.
  2. The data is included in dynamic content that is sent to a web user without being validated for malicious code.
The malicious content sent to the web browser often takes the form of a segment of JavaScript, but may also include HTML, Flash or any other type of code that the browser may execute. The variety of attacks based on XSS is almost limitless, but they commonly include transmitting private data like cookies or other session information to the attacker, redirecting the victim to web content controlled by the attacker, or performing other malicious operations on the user's machine under the guise of the vulnerable site.

The XSS attacks are in two categories.


Stored XSS Attacks

Stored attacks are those where the injected code is permanently stored on the target servers, such as in a database, in a message forum, visitor log, comment field, etc. The victim then retrieves the malicious script from the server when it requests the stored information.

Reflected XSS Attacks

Reflected attacks are those where the injected code is reflected off the web server, such as in an error message, search result, or any other response that includes some or all of the input sent to the server as part of the request. Reflected attacks are delivered to victims via another route, such as in an e-mail message, or on some other web server. When a user is tricked into clicking on a malicious link or submitting a specially crafted form, the injected code travels to the vulnerable web server, which reflects the attack back to the user’s browser. The browser then executes the code because it came from a "trusted" server.
 


The site OWASP offers a great way to protect your site from a XSS attack.

OWASP XSS Cheat Sheet

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