The issue is related to the function `add option()` in ISC DHCP, which is used in server responses to lease query packets. When `option code hash lookup()` is called from `add option()`, it increases the option's `refcount` field, but there is no corresponding call to `option dereference()` to decrement the `refcount` field. This can cause the reference counters to overflow, leading to a server abort. The vulnerability can be exploited by a remote attacker to cause a denial of service.