The Plack::Middleware::XSRFBlock package before 0.0.19 for Perl allows attackers to bypass a CSRF protection mechanism via an empty form value and an empty cookie (if signed cookies are disabled).
The web application does not, or cannot, sufficiently verify whether a request was intentionally provided by the user who sent the request, which could have originated from an unauthorized actor.
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.