Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
remark-html is an open source nodejs library which compiles Markdown to HTML. In affected versions the documentation of remark-html has mentioned that it was safe by default. In practice the default was never safe and had to be opted into. That is, user input was not sanitized. This means arbitrary HTML can be passed through leading to potential XSS attacks. The problem has been patched in 13.0.2 and 14.0.1: `remark-html` is now safe by default, and the implementation matches the documentation. On older affected versions, pass `sanitize: true` if you cannot update.
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.