CVE-2026-120633

CGI versions before 5.00 for Perl trust the client X-Forwarded-Host header in url, self url, virtual host and virtual port.

These take the host name and port from the X-Forwarded-Host request header when present, and otherwise from Host, without validating either. The URLs from url and self url are the default redirect location and the start html(-base=>1) base href, and the default start form action when REQUEST URI is not set.

A client can poison shared caches, and URLs the application stores or sends, with redirects, links and scripts that point at a host it controls.