CVE-2026-42534
Publiée le 2026-05-20 · Dernière modification le 2026-09-01
Les résolveurs DNS Unbound en version 1.25.0 et antérieures sont sensibles à une faille de dégradation des performances. Un attaquant distant non authentifié peut ralentir ou bloquer complètement la résolution DNS pour d'autres utilisateurs en envoyant des requêtes spécifiques et en contrôlant un serveur de noms faisant autorité à réponse lente. Cette attaque est relativement facile à exécuter car elle ne nécessite aucun privilège particulier ni interaction de l'utilisateur, seulement un accès réseau au résolveur.
DÉTAIL DU VECTEUR CVSS
RÉFÉRENCES
Description officielle du NVD (en anglais)
NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the jostle logic that could defeat its purpose and degrade resolution performance. Retransmits of the same query could renew the age of slow running queries and not allow the jostle logic to see them as aged and potential targets for replacement with new queries. An adversary who can query a vulnerable Unbound and who can control a domain name server that replies slowly and/or maliciously to Unbound's queries can exploit the vulnerability and degrade the resolution performance of Unbound. When Unbound's 'num-queries-per-thread' reaches its limit, the jostle logic kicks in. When a new query comes in, half of the available queries that are also slow to resolve are candidates for replacement. The vulnerability then happens because duplicate queries that need resolution would skew the aging result by using the timestamp of the latest duplicate query instead of the original one that started the resolution effort. Cache and local data response performance remains unaffected. Coordinated attacks could raise this to a denial of resolution service. Unbound 1.25.1 contains a patch with a fix to attach an initial, non-updatable start time for incoming queries that allow the jostle logic to work as intended.