It depends on the CLA. Some just require you to affirm that you have the rights to license your contribution, and that you license it under the license of the p

It depends on the CLA. Some just require you to affirm that you have the rights to license your contribution, and that you license it under the license of the project, which is indeed mostly just a CYA. It doesn't allow the project to unilaterally change the license of your contribution, and I haven't seen much people have a problem with this kind of CLA. The other common form of CLA is a copyright assignment (or something equivalent) to a foundation or company representing the project, which is much more troublesome. This allows them to basically do whatever they want with your contribution, including charging for it, or closing the source all together.