Today Sophos released UTM 9.604-2. The release will be rolled out in phases.

In phase 1 you can download the update package from their FTP server, in phase 2they will spread it via their Up2Date servers.

Up2Date 9.604002 package description:

Remarks:
System will be rebooted
Connected APs will perform firmware upgrade

News:
Security Release

Bugfix:
Fix [NUTM-11036]: [Kernel] TCP SACK PANIC – Kernel vulnerabilities

RPM packages contained:
firmwares-bamboo-9400-0.326544518.g310ee6c.rb1.i586.rpm
perf-tools-3.12.74-0.327535988.gc5bb1a9.i686.rpm
kernel-smp-3.12.74-0.327535988.gc5bb1a9.i686.rpm
kernel-smp64-3.12.74-0.327535988.gc5bb1a9.x86_64.rpm
ep-release-9.604-2.noarch.rpm