Reflected XSS in GoCD

GoCD is a continuous delivery server. GoCD versions 20.2.0 until 21.4.0 are vulnerable to reflected cross-site scripting via abuse of the pipeline comparison function's error handling to render arbitrary HTML into the returned page. This could allow an attacker to trick a victim into executing code which would allow the attacker to operate on, or gain control over the same resources as the victim had access to. This issue is fixed in GoCD 21.4.0. As a workaround, block access to `/go/compare/.*` prior to GoCD Server via a reverse proxy, web application firewall or equivalent, which would prevent use of the pipeline comparison function.