JQ::Lite versions before 2.51 for Perl execute Perl code embedded in a query's regular expression by compiling it with string eval. The pattern given to test(), match(), or the match and =~ conditions of select() is placed in a "qr'...'" literal and compiled as source text, so a "(?{ ... })" code block in it runs without "use re 'eval'". Single quotes in the pattern are escaped, but a code block runs in place and needs none. An attacker who supplies a query, or text that an application inserts into the pattern of one, can execute arbitrary Perl code in the calling process.