SQL::Abstract versions from 1.90_01 before 2.000001_04 for Perl skip the injection_guard check for function names given with -func.
injection_guard is documented to apply to every function name, but only the { -name => ... } shorthand goes through it. The explicit { -func => [ $name, ... ] } form puts $name into the SQL unchecked.
An application that relies on injection_guard to reject an untrusted function name passed with -func allows SQL injection.
Upgrade to SQL-Abstract 2.000001_04 or later.