It is not just GPS guidance. Iran has at least these kinds of sensors for its missiles: electro-optical, thermal, and passive radar. Some missiles have dual sensors. Some missiles do visual recognition of targets. Some missiles work just like an anti-radiation missile would.According this history legends analysis at 14:46 that the Iranians are probably targeting Israeli air defense batteries with their missiles. If that is correct.
1- The Iranians have access to real intelligence data either by real time satellite or they did a reverse uno to the Israelis Mossad
2- The CEP of their missiles is basically 30-80 meters and they may have access to some sort of military grade GNSS positioning.