Rashi: Those who look to and hope for Kush's help and boast about the support of Egypt.

Radak: Yisrael, i.e. Yehudah, Binyamin and a small remnant from the 10 tribes, which were almost totally exiled. They trusted in Kush and Egypt, for they were at war with Melech Ashur. We find that Tirhakah Melech Kush went to fight Sancheriv (37:9). They hoped to be saved from Ashur via Kush. When Kush and Egypt fell, they were afraid and embarrassed.

Malbim: Those who looked for Kush's help were afraid, for now they have no hope. Those who glorified themselves about the honor of Egypt and their covenant with them, but did not look to them for help, are ashamed that initially they glorified themselves.