Then again, Vodafone Portugal was caught rewriting CSPs of all your visited pages to whitelist their own domain last year [0].
[0]: https://twitter.com/JackyHallyday/status/968263408003973121
[0]: https://twitter.com/JackyHallyday/status/968263408003973121
However, "was caught" is important :) The more noise they make the more likely they are to get caught.