OpenSSH 10.4 Released With Security Fixes and SSH Protocol Hardening

OpenSSH 10.4 (10.4p1) was released on July 6, 2026, introducing transport protocol hardening that disconnects peers sending non-key-exchange messages during key re-exchange (closing a denial-of-service/resource-exhaustion vector), stricter seccomp and NO_NEW_PRIVS enforcement on Linux (now fatal if unsupported), and a change to sshd -G which emits mixed-case directives that may break automation; administrators should test automation and kernel support before upgrading and consider auditing other SSH implementations for RFC 4253 compliance.