CallBackery versions before 0.62.0 for Perl accept unintended values in form fields checked by createRxValidator. createRxValidator() is documented to anchor the supplied pattern at both ends, but builds /^${rx}$/ without grouping the pattern. An alternation such as yes|no then accepts any value starting with yes or ending with no, and $ also accepts a value with one trailing newline. An authenticated user can submit values the pattern was meant to reject, which an application may then write into generated configuration files.