CVE-2026-93007

A flaw was found in dnsmasq. The TCP DNS service uses a small fixed pool of child processes and does not set a receive timeout on client connections. A remote attacker can open idle TCP connections to port 53 and occupy the entire pool, preventing new TCP DNS connections and DNSSEC validation that requires TCP fallback. UDP DNS resolution continues, and occupied slots are released after a fixed lifetime.

This vulnerability is rated as Moderate because UDP DNS continues during exhaustion, the effect auto-recovers after 150 seconds unless the attacker reconnects, and availability impact is Low rather than High. Only TCP-dependent operations (DNSSEC TCP fallback, zone transfers, TCP-only clients) are disrupted. Red Hat products that ship dnsmasq as a DNS forwarder are affected. Administrators can raise --max-tcp-connections and apply firewall connection limits.

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.

The following measures reduce risk:

1. Increase the TCP connection limit with --max-tcp-connections=<N> to raise the number of connections an attacker must hold.
2. Limit per-source TCP connections to port 53 with firewall rules, for example iptables connlimit on tcp/53.
3. Restrict which hosts can reach TCP port 53 if TCP DNS is not required from untrusted networks.