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.
No fixed release is available. In 0.712 and later, set the uri_base configuration key to the application's own base URL; otherwise reject requests whose host is not an expected application hostname, including X-Forwarded-Host under behind_proxy.