Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
setup/controllers/language.php in MODX Revolution 2.5.4-pl and earlier does not properly constrain the language parameter, which allows remote attackers to conduct Cookie-Bombing attacks and cause a denial of service (cookie quota exhaustion), or conduct HTTP Response Splitting attacks with resultant XSS, via an invalid parameter value.
CWE-79 - Cross Site Scripting
Cross-Site Scripting, commonly referred to as XSS, is the most dominant class of vulnerabilities. It allows an attacker to inject malicious code into a pregnable web application and victimize its users. The exploitation of such a weakness can cause severe issues such as account takeover, and sensitive data exfiltration. Because of the prevalence of XSS vulnerabilities and their high rate of exploitation, it has remained in the OWASP top 10 vulnerabilities for years.