I havent tested this, but I think URL.GetParameter("status") matches "*abc* would work. If it doesnt it may only apply to GET parameters rather than POST parameters.
You can use regular expression against Body.Text property, especially if you combine it with Body.MimeTypeEnsured == "application/x-www-url-encoded"
It worked! Thanks!
I made the rule little more specific by adding URL property along with ensured media type and body.text.