A use-after-free vulnerability was found in the tc_new_tfilter function in net/sched/cls_api.c in the Linux kernel. The availability of local, unprivileged user namespaces allows privilege escalation.

Mitigation

On non-containerized deployments of Red Hat Enterprise Linux 8, you can disable user namespaces by setting user.max_user_namespaces to 0:

echo "user.max_user_namespaces=0" > /etc/sysctl.d/userns.conf

sysctl -p /etc/sysctl.d/userns.conf

On containerized deployments, such as Red Hat OpenShift Container Platform, do not use this mitigation as the functionality is needed to be enabled.