Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
In Drupal 8.0.x prior to 8.8.10, 8.9.x prior to 8.9.6, and 9.0.x prior to 9.0.6, a Reflected Cross-site Scripting (XSS) vulnerability exists under certain circumstances that would allow an attacker could leverage the way that HTML is rendered for affected forms in order to exploit the vulnerability.
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.