In FRRouting (FRR) through 9.1, it is possible for the get_edge() function in ospf_te.c in the OSPF daemon to return a NULL pointer. In cases where calling functions do not handle the returned NULL value, the OSPF daemon crashes, leading to denial of service.
https://github.com/FRRouting/frr/pull/15674/commits/34d704fb0ea60dc5063af477a2c11d4884984d4f