CVE-2026-42923— Degradation of service with unbounded NSEC3 hash calculations

Degradation of service with unbounded 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.

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算法复杂性

NLnet Labs Unbound 安全漏洞

NLnet Labs Unbound是NLnet Labs开源的一个高性能DNS解析器。 NLnet Labs Unbound 1.25.0及之前版本存在安全漏洞，该漏洞源于DNSSEC验证器中查询DS记录负缓存时未考虑NSEC3哈希计算限制，可能导致服务降级，攻击者通过签名高迭代次数的NSEC3记录并查询可消耗哈希计算资源，同时持有全局锁阻塞其他线程。

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