CVE-2026-40691

A flaw was found in Unbound, a domain name system (DNS) resolver. When Unbound is configured with DNSCrypt support, a remote attacker could send a specially crafted DNSCrypt query over TCP. This malicious query could cause a memory error, leading to a server crash and a Denial of Service (DoS). This means legitimate users would be unable to access services relying on the Unbound server.

This is an Important denial of service vulnerability affecting Unbound when built with DNSCrypt support. A remote attacker can trigger a heap overflow by sending a specially crafted DNSCrypt query over TCP, leading to a server crash and disruption of DNS resolution services. This vulnerability doesn't impact any supported the versions of unbound as shipped with Red Hat Enterprise Linux as it is not compiled with DNSCrypt support.

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.