Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
All versions of io.ratpack:ratpack-core from 0.9.9 inclusive and before 1.7.6 are vulnerable to Cross-site Scripting (XSS). This affects the development mode error handler when an exception message contains untrusted data. Note the production mode error handler is not vulnerable - so for this to be utilized in production it would require users to not disable development mode.
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.