Plack::Middleware::CSP versions before 0.03 for Perl send the Content Security Policy under the wrong header name, so browsers never enforce it.
The call method sets the policy in a response header named "content-security-protocol" instead of "Content-Security-Policy". Browsers ignore that header.
Any cross-site scripting flaw in the wrapped application can run scripts the policy was meant to block.
Incorrect Provision of Specified Functionality The code does not function according to its published specifications, potentially leading to incorrect usage.