I also hate regex but in theory something like this might work
\d{1,3}(\.\d{1,3}){3}
this should look for 0-9 between 1 and 3 times then a dot followed by 1-3 numbers 3 times. In practise limited repetition ({1,3} etc.) is not always supported and you may be forced to use + instead. Occasionally \d isn't supported either in which case you can replace it with [0-9].
Filled with hate