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. It is listed as CWE-79: "Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')" in the Common Weakness Enumeration. The OWASP Web Security Testing Guide (WSTG) 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. The use of a carefully crafted Content-Security-Policy can also be part of a defense-in-depth approach. Additionally, applications should be regularly tested for any reflected XSS vulnerabilities. OWASP provides a cheat sheet for prevention of Cross Site Scripting.