A NULL pointer dereference flaw was found in Libreswan when processing IKEv1 Quick Mode requests. When an IKEv1 Quick Mode connection configured with ID_IPV4_ADDR or ID_IPV6_ADDR receives an IDcr payload with ID_FQDN, it triggers a NULL pointer dereference error. This flaw allows a malicious client or attacker to send a malformed IKEv1 Quick Mode packet, causing a crash and restart of the libreswan pluto daemon. When sent continuously, this issue leads to a denial of service attack.