Description
Cross-site Scripting (XSS) refers to client-side code injection attack wherein an attacker can execute malicious scripts into a legitimate website or web application. XSS occurs when a web application makes use of unvalidated or unencoded user input within the output it generates. The severity level of this vulnerability instance has been lowered to take into account that a victim would have to use a client that does not encode quote characters (", ') inside query strings.
Remediation
Apply context-dependent encoding and/or validation to user input rendered on a page
References
Cross-site Scripting (XSS) Attack - Acunetix
XSS Filter Evasion Cheat Sheet
Excess XSS, a comprehensive tutorial on cross-site scripting
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