Text::CSV_XS versions before 1.65 for Perl leak the parsed fields of a record that fails to parse in getline.
getline collects the fields of a record into a new array and returns a reference to it only when the parse succeeds. When the record has a syntax error, getline returns undef and never frees the array or the fields parsed before the error.
A long-running process parsing untrusted CSV retains every malformed record it is sent, so repeated malformed input exhausts its memory.
Upgrade to Text-CSV_XS 1.65 or later.