cyberstrikeus Ensure Userland Proxy is Disabled (Manual)
Profile Applicability
• Level 1 - Docker - Linux
Description
The Docker daemon starts a userland proxy service for port forwarding whenever a port is exposed. Where hairpin NAT is available, this service is generally superfluous to requirements and can be disabled.
Rationale
The Docker engine provides two mechanisms for forwarding ports from the host to containers, hairpin NAT, and the use of a userland proxy. In most circumstances, the hairpin NAT mode is preferred as it improves performance and makes use of native Linux iptables functionality instead of using an additional component.
Where hairpin NAT is available, the userland proxy should be disabled on startup to reduce the attack surface of the installation.
Impact
Some systems with older Linux kernels may not be able to support hairpin NAT and therefore require the userland proxy service. Also, some networking setups can be impacted by the removal of the userland proxy.
Audit Procedure
To confirm this setting, you should review the dockerd start-up options and any settings in /etc/docker/daemon.json.
To review the dockerd startup options, use:
ps -ef | grep dockerd
Ensure that the --userland-proxy parameter is set to false.
The contents of /etc/docker/daemon.json should also be reviewed for this setting.
Remediation
You should run the Docker daemon as below:
dockerd --userland-proxy=false
Default Value
By default, the userland proxy is enabled.
References
- http://windsock.io/the-docker-proxy/
- https://github.com/docker/docker/issues/14856
- https://github.com/docker/docker/issues/22741
- https://docs.docker.com/config/containers/container-networking/
CIS Controls
Controls Version: v8
Control: 4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software
Uninstall or disable unnecessary services on enterprise assets and software, such as an unused file sharing service, web application module, or service function.
IG 1: IG 2: ● IG 3: ●
Controls Version: v7
Control: 9.2 Ensure Only Approved Ports, Protocols and Services Are Running
Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.
IG 1: IG 2: ● IG 3: ●