CGI::Carp versions before 5.00 for Perl leak warnings across requests in persistent environments via the warningsToBrowser buffer.
Warnings are held in a package-level buffer until warningsToBrowser writes them into the page as HTML comments, and the buffer is never cleared between requests. Under mod_perl, FastCGI or PSGI, warnings from one request are written into a later one.
Warnings that contain one user's request data can appear in the HTML sent to another user.
Exposure of Data Element to Wrong Session The product does not sufficiently enforce boundaries between the states of different sessions, causing data to be provided to, or used by, the wrong session.