CVE-2026-50252

A flaw in Unbound's SO_REUSEPORT implementation reduces UDP source port entropy by allowing attackers to map ports to specific worker threads. This enables DNS cache poisoning, potentially leading to traffic redirection or unauthorized information disclosure.

Moderate: This flaw allows for DNS cache poisoning due to predictable UDP source ports when Unbound's so-reuseport option is enabled by default. An attacker on an adjacent network can exploit this to compromise the integrity of DNS resolutions, leading to potential redirection of traffic.

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.

Disable the so-reuseport option by explicitly setting so-reuseport: no in your unbound.conf file. This prevents the deterministic mapping of worker threads to outbound UDP source ports, effectively stopping the cache poisoning vector. Additionally, restrict who can query the resolver using the access-control directive to reduce the overall attack surface, and restart the Unbound service to apply the changes.