CVE-2026-15689: Dancer2::Plugin::Auth::Extensible versions through 0.713 for Perl allow password reset link poisoning via the request Host header in _default_email_password_reset and _default_welcome_send

Dancer2::Plugin::Auth::Extensible versions through 0.713 for Perl allow password reset link poisoning via the request Host header in _default_email_password_reset and _default_welcome_send. Both default emails emit a link of the form `$base/login/$code`, whose authority comes from the request Host header, or from X-Forwarded-Host under behind_proxy (obtained from Dancer2's request->base function). A POST to /login carrying submit_reset and a username needs no authentication: it stores a fresh reset code against that account and mails the account holder a link to a host of the sender's choosing. The welcome mail takes the same path when the application calls create_user with email_welcome set. Through 0.711 the handlers read `request->uri_base` and `request->base` directly; Versions 0.712 and later provide an uri_base configuration key that defaults to the untrusted `request->uri_base` when unset. The default configuration with reset_password_handler enabled and the default message text, a recipient who follows the link hands a working reset code to the sender's host, which is enough to take over the account.