CVE-2026-55717

Beschreibung

In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when -serve-expired: yes- is set together with a -response-ip: <net> redirect- /-response-ip-data: <net> CNAME <target>- rule (or the RPZ -rpz-cname-override- equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets -alias_rrset- but not -partial_rep-. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of -serve-expired-client-timeout- is taken leading to denial of service via the server crash.