Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
In Metinfo 6.1.3, include/interface/applogin.php allows setting arbitrary HTTP headers (including the Cookie header), and common.inc.php allows registering variables from the $_COOKIE value. This issue can, for example, be exploited in conjunction with CVE-2018-19835 to bypass many XSS filters such as the Chrome XSS filter.
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.