CVE-2026-41637

A flaw was found in Unbound, a Domain Name System (DNS) resolver. A remote attacker can exploit this vulnerability by sending and immediately terminating DNS-over-QUIC (DoQ) queries. This improper handling of terminated queries can lead to a build-up of pending responses, causing a degradation of service for new clients and ultimately a Denial of Service (DoS).

This vulnerability is rated as Low impact. Unbound, as distributed in Red Hat products, is not typically configured with DNS-over-QUIC (DoQ) support enabled by default. Exploitation requires Unbound to be explicitly compiled with --with-libngtcp2 and have quic-port configured, in addition to an attacker bypassing default rate limits with multiple source IPs. This makes successful exploitation difficult in standard Red Hat deployments.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, completely disable DNS-over-QUIC (DoQ) support by removing or commenting out the quic-port directive in your Unbound configuration. Restart the Unbound service to apply the changes and clear any lingering resource limits.