Which of the following is true about the legality of overflights?

Overflights are legal under certain conditions as governed by international law, national regulations, and agreements between countries. The principle of freedom of overflight is recognized in international law, particularly as articulated in the Chicago Convention on International Civil Aviation. This principle allows for civil aircraft to fly over the territory of a state without prior permission under specified circumstances. Additionally, countries often specify airspace that is open versus restricted, but in general, overflights do not require special permits unless one is operating within restricted airspace or engaging in specific activities that could raise legal or security issues.

The other choices suggest limitations or prohibitions that do not generally apply to the concept of overflights in a broad legal sense. While special permits might sometimes be required for specific types of overflights or in restricted airspace, the fundamental principle is that many overflights are indeed legal without those permits, making the first option the most accurate representation of the legality of overflights in general.