IPFire < v2.29 Stored XSS via Multiple Methods in cleanhtml()

IPFire versions prior to 2.29 (Core Update 198) contain multiple stored cross-site scripting (XSS) vulnerabilities caused by a bug in the cleanhtml() function (/var/ipfire/header.pl) that fails to apply HTML-entity encoding to user input. When an authenticated user submits data to affected endpoints - for example, POST /cgi-bin/wakeonlan.cgi (CLIENT_COMMENT), /cgi-bin/dhcp.cgi (ADVOPT_DATA, FIX_REMARK, FIX_FILENAME, FIX_ROOTPATH), /cgi-bin/connscheduler.cgi (ACTION_COMMENT), /cgi-bin/dnsforward.cgi (REMARK), /cgi-bin/vpnmain.cgi (REMARK), or /cgi-bin/dns.cgi (REMARK) - the application calls escape() and HTML::Entities::encode_entities() but never assigns the sanitized result back to the output variable. The original unsanitized value is therefore stored and later rendered in the web interface without proper sanitation or encoding, allowing injected scripts to execute in the context of other users who view the affected entries.