CVE-2026-77692

ISC BIND 9 contains a NULL pointer dereference (CWE-476) that causes the `named` daemon to abort when it receives a DNS-over-HTTPS request carrying a cryptographically invalid SIG(0) record followed by a premature close of the transport connection. An unauthenticated remote attacker can trigger the crash repeatedly, achieving a denial of service with no confidentiality or integrity impact (CVSS availability-only). Only deployments running affected 9.20.x, 9.21.x, or 9.20.x-S1 versions with DoH listeners configured are exposed; servers without DoH endpoints enabled are not vulnerable. No public proof-of-concept exists, the flaw is not in the CISA KEV catalog, and no exploitation in the wild has been reported.

What to do: Upgrade to the patched releases published by ISC for the 9.20, 9.21, and 9.20-S1 branches (see the corresponding ISC advisory for exact fixed version numbers). As an interim mitigation, disable or remove DNS-over-HTTPS (http) listeners in named.conf, or restrict DoH endpoints at the firewall/ACL level to trusted clients. Check whether your named.conf defines http endpoints and whether port 443 DoH service is internet-facing; if not, your exposure is limited.