Sorry; I didn't actually inspect the link I sent previously to verify that it had no clicks at all to
http://cr.yp.to/softwarelaw.html
which says, once you legally obtain software, you may modify it, if you have the time and inclination.
So that's the "default license" that is present without any license grant being explicitly made on the part of an IP owner who for instance uploads something to CPAN without specifying a license for it.