Input Validation / Reflected Cross Site Scripting
Description
Reflected Cross-Site Scripting (XSS) is a type of computer security vulnerability typically found in web applications. It occurs when user input is not properly sanitized and is reflected back to the user in the application’s response. This type of attack can be used to inject malicious client-side scripts into a web page viewed by other users. According to the Common Weakness Enumeration (CWE) directory, Reflected XSS is defined as “a type of injection attack in which an attacker injects or manipulates input that the web application or server reflects back to the user in the response.” The OWASP Testing Guide provides further guidance on how to identify and test for this type of vulnerability.
Risk
Reflected XSS poses a high risk to web applications as it can be used to inject malicious client-side scripts into the user’s browser. This type of attack can be used to steal user credentials, hijack user sessions, or even deface web pages. The potential impact of this vulnerability is significant as it can lead to data loss, loss of reputation, or even financial loss.
Solution
The best way to mitigate the risk of Reflected XSS is to sanitize user input by validating, encoding, or filtering it. All user input should be treated as if it is malicious and should be escaped or encoded before being included in the application’s response. This will ensure that any malicious code is prevented from executing in the user’s browser.
Example
The following code contains a reflected XSS vulnerability.
<html>
<body>
<?php
$name = $_GET['name'];
echo "Hello, " . $name;
?>
</body>
</html>
The code contains a reflected XSS vulnerability because the user-supplied data stored in the $name variable is reflected back in the application’s response without any sanitation or encoding. This could allow an attacker to inject malicious code into the application’s response, which would then be executed in the user’s browser.