CVE-2026-55990

A flaw was found in Unbound when configured with DNSCrypt support. An unauthenticated remote attacker could exploit a faulty configuration, where an imbalance between DNSCrypt provider certificate and secret key files leads to memory corruption. By sending a specially crafted network request, the attacker can cause a garbage dereference, leading to a server crash and a denial of service (DoS).

This Moderate flaw in Unbound can lead to a denial of service if the DNSCrypt feature is enabled and misconfigured. Exploitation requires Unbound to be compiled with DNSCrypt support, which is not a default setting in Red Hat products, and a specific mismatch between DNSCrypt provider certificate and secret key files. An unauthenticated attacker could then send a crafted UDP packet to trigger a server crash.

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, ensure that Unbound is not compiled with DNSCrypt support if the feature is not required. If DNSCrypt support is enabled, verify that the number of 'dnscrypt-provider-cert:' files precisely matches the number of 'dnscrypt-secret-key:' files in the Unbound configuration to prevent the faulty configuration that leads to a denial of service. Restart the Unbound service after any configuration changes.