GHSA-x4rx-4gw3-53p4 — Moby firewalld reload makes published container ports accessible from remote hosts

Affected: Go: github.com/docker/docker

Moby is an open source container framework developed by Docker Inc. that is distributed as Docker Engine, Mirantis Container Runtime, and various other downstream projects/products. The Moby daemon component (dockerd), which is developed as [moby/moby](https://github.com/moby/moby) is commonly referred to as Docker, or Docker Engine.

Firewalld is a daemon used by some Linux distributions to provide a dynamically managed firewall. When Firewalld is running, Docker uses its iptables backend to create rules, including rules to isolate containers in one bridge network from containers in other bridge networks.

### Impact

The iptables rules created by Docker are removed when firewalld is reloaded using, for example "firewall-cmd --reload", "killall -HUP firewalld", or "systemctl reload firewalld".

When that happens, Docker must re-create the rules. However, in affected versions of Docker, the iptables rules that prevent packets arriving on a host interface from reaching container addresses are not re-created.

Once these rules have been removed, a remote host configured with a route to a Docker bridge network can access published ports, even when those ports were only published to a loopback address. Unpublished ports remain inaccessible.

For example, following a firewalld reload on a Docker host with address `192.168.0.10` and a bridge network with subnet `172.17.0.0/16`, running the following command on another host in the local network will give it access to published port…

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GHSA-x4rx-4gw3-53p4 — Moby firewalld reload makes published container ports accessible from remote hosts