ApostropheCMS is an open-source Node.js content management system. Versions up to and including 4.29.0 have a password reset flow that constructs the reset URL using "req.hostname", which is derived directly from the attacker-controlled HTTP "Host" header when "apos.baseUrl" is not explicitly configured. An unauthenticated attacker who knows a victim's email address can send a crafted reset request that causes the application to email the victim a reset link pointing to the attacker's domain. When the victim clicks the link, the valid reset token is delivered to the attacker, enabling full account takeover. As of time of publication, no known patched versions are available.