A use-after-free flaw was found in the packet processing context in net/netfilter/x_tables.c in netfilter in the Linux Kernel. This issue occurs when the per-CPU sequence count is mishandled during concurrent iptables rules replacement and can be exploited with the CAP_NET_ADMIN capability in an unprivileged namespace.

Mitigation

In order to trigger the issue, it requires the ability to create user/net namespaces.

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.