5.30 Ensure that the host's user namespaces are not shared

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Information

You should not share the host's user namespaces with containers running on it.

Rationale:

User namespaces ensure that a root process inside the container will be mapped to a non-root process outside the container. Sharing the user namespaces of the host with the container does not therefore isolate users on the host from users in the containers.

Impact:

None

Solution

You should not share user namespaces between host and containers.
For example, you should not run the command below:

docker run --rm -it --userns=host ubuntu bash

Default Value:

By default, the host user namespace is shared with containers unless user namespace support is enabled.

See Also

https://workbench.cisecurity.org/files/3353