Is it permissible to wipe over the headscarf while performing wudu?

In order for the wiping of the head to be valid, the wetness must touch at least one-fourth of the head. Therefore, wiping over items such as a headscarf, cap, or wig that prevent the wetness from reaching the head is not valid. (Kâsânî, Bedâ’i, 1/4-5; Merghinani, al-Hidaya, 1/32) However, women may wipe their heads during wudu by inserting their hands under their headscarves without removing them. This is because the Prophet (peace be upon him) wiped his head by inserting his hand under his turban without removing it. (Abu Dawud, Taharah, 57 [150, 153])

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu