Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Connect before 2.8.2 is vulnerable to Cross-Site Scripting (XSS). The "methodOverride" middleware allows the http post to override the method of the request, and because the user post input was not checked, req.method could contain any kind of value. Because the req.method did not match any common method VERB, connect answered with a 404 page. The method was not properly encoded for output in the browser.
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.