Описание
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: redirect' /'response-ip-data: CNAME ' 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.
A flaw in Unbound allows a remote attacker controlling a delegated domain to trigger a NULL pointer dereference and crash the daemon. Exploitation occurs when serve-expired: yes and specific response-ip or RPZ rules are configured, resulting in a denial of service.
Отчет
This Moderate severity denial of service flaw in Unbound requires specific configurations, including serve-expired: yes and either response-ip or RPZ CNAME override rules. Exploitation depends on a remote attacker controlling a delegated domain and delaying DNS responses, which limits the immediate impact on typical Red Hat Unbound deployments not utilizing these advanced features.
Меры по смягчению последствий
Ensure serve-expired remains disabled (default), or set serve-expired-client-timeout: 0 to bypass the vulnerable callback path. If serving expired answers is necessary, remove any response-ip CNAME redirect rules and RPZ rpz-cname-override entries. Additionally, use access-control to restrict query access, preventing untrusted clients from triggering the flaw via attacker-controlled names.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | unbound | Fix deferred | ||
| Red Hat Enterprise Linux 6 | unbound | Not affected | ||
| Red Hat Enterprise Linux 7 | unbound | Not affected | ||
| Red Hat Enterprise Linux 8 | unbound | Fix deferred | ||
| Red Hat Enterprise Linux 9 | unbound | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Not affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Fix deferred | ||
| Red Hat Hardened Images | unbound-main-1.25.2-0.1.hum1 | Fixed | RHSA-2026:43588 | 22.07.2026 |
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Дополнительная информация
Статус:
5.9 Medium
CVSS3
Связанные уязвимости
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.
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.
'serve-expired-client-timeout' and 'response-ip' CNAME redirect could lead to a crash
In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-e ...
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.
5.9 Medium
CVSS3