CGI versions before 5.00 for Perl return request-derived values untainted under taint mode.
The upload filename, uploadInfo values, some path_info and script_name values, Accept results, and the name lists from url_param and cookie are returned without the taint flag, as is a cookie named expires from 4.67 on.
These values come from regex captures or hash keys, which Perl does not taint, so they pass -T checks unvalidated.
Upgrade to CGI 5.00 or later.