Описание
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.
A flaw was found in Unbound's DNSSEC validator where the code path for consulting the negative cache for DS records does not honor the limit on NSEC3 hash calculations introduced in version 1.19.1. An adversary who controls a DNSSEC-signed zone can sign NSEC3 records with high iteration counts for child delegations, causing Unbound to perform excessive hash computations while holding a global lock on the negative cache. This temporarily blocks other resolver threads from accessing the negative cache, leading to degraded DNS resolution performance for the duration of the attack.
Отчет
The Red Hat Product Security team has assessed the severity of this vulnerability as Moderate. The flaw can be remotely triggered without authentication, but the impact is limited to service degradation rather than a full denial-of-service.The Unbound process does not crash,a global negative cache lock is held during excessive NSEC3 hash computations, temporarily blocking other resolver threads. The root cause is a negative cache code path that bypasses the existing NSEC3 hash computation limits.
Меры по смягчению последствий
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | unbound | Fix deferred | ||
| Red Hat Enterprise Linux 6 | unbound | Fix deferred | ||
| Red Hat Enterprise Linux 7 | unbound | Fix deferred | ||
| Red Hat Enterprise Linux 8 | unbound | Fix deferred | ||
| Red Hat Enterprise Linux 9 | unbound | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | rhcos | Fix deferred | ||
| Red Hat Hardened Images | unbound-main-1.25.1-1.hum1 | Fixed | RHSA-2026:20357 | 23.05.2026 |
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Дополнительная информация
Статус:
EPSS
5.3 Medium
CVSS3
Связанные уязвимости
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the DNSSEC validator where the code path to consult the negative cache for DS records does not take into account the limit on NSEC3 hash calculations introduced in 1.19.1. This leads to degradation of service during the attack. An adversary that controls a DNSSEC signed zone can exploit this by signing NSEC3 records with acceptably high iterations for child delegations and querying a vulnerable Unbound. Unbound will keep performing the allowed hash calculations on the NSEC3 records and will not limit the work by the mitigation introduced in 1.19.1. As a side effect, a global lock for the negative cache will be held for the duration of the hashing, blocking other threads that need to consult the negative cache. Coordinated attacks could raise the vulnerability to denial of service. Unbound 1.25.1 contains a patch with a fix to bound the vulnerable code path with the existing limit for NSEC3 hash calculations.
Degradation of service with unbounded NSEC3 hash calculations
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerabil ...
EPSS
5.3 Medium
CVSS3