Moby is an open source container framework that is a key component of Docker Engine, Docker Desktop, and other distributions of container tooling or runtimes. In 26.0.0, IPv6 is not disabled on network interfaces, including those belonging to networks where --ipv6=false. An container with an ipvlan or macvlan interface will normally be configured to share an external network link with the host machine.

Because of this direct access, (1) Containers may be able to communicate with other hosts on the local network over link-local IPv6 addresses, (2) if router advertisements are being broadcast over the local network, containers may get SLAAC-assigned addresses, and (3) the interface will be a member of IPv6 multicast groups. This means interfaces in IPv4-only networks present an unexpectedly and unnecessarily increased attack surface. The issue is patched in 26.0.2.

To completely disable IPv6 in a container, use --sysctl=net.ipv6.conf.all.disable_ipv6=1 in the docker create or docker run command. Or, in the service configuration of a compose file.