validate against special characters *; ' * ^ } { [ ] ><|

My regexp kung-fu is not the strongest, but it looks like you’ve only allowed for a single charachter here.

You may need to allow for some more

validates_format_of /^[^thesechars]+$/

You may want to consider this around the other way though. Instead of forbidding chars, allow a restricted set.

validates_format_of /^\w+$/ will restrict the values allowable
(maybe too much so). You’ll need to check the docs to tune it to
your specific need.