Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Redcarpet is a Ruby library for Markdown processing. In Redcarpet before version 3.5.1, there is an injection vulnerability which can enable a cross-site scripting attack. In affected versions no HTML escaping was being performed when processing quotes. This applies even when the ":escape_html" option was being used. This is fixed in version 3.5.1 by the referenced commit.
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.