RHEL 9 must disable the use of user namespaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257816	RHEL-09-213105	SV-257816r942981_rule		Medium

Description
User namespaces are used primarily for Linux containers. The value "0" disallows the use of user namespaces.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2023-12-01

Details

Check Text ( C-61557r942980_chk )
Verify RHEL 9 disables the use of user namespaces with the following commands: Note: User namespaces are used primarily for Linux containers. If containers are in use, this requirement is Not Applicable. $ sudo sysctl user.max_user_namespaces user.max_user_namespaces = 0 If the returned line does not have a value of "0", or a line is not returned, this is a finding. Check that the configuration files are present to enable this kernel parameter. $ sudo /usr/lib/systemd/systemd-sysctl --cat-config \| egrep -v '^(#\|;)' \| grep -F user.max_user_namespaces \| tail -1 user.max_user_namespaces = 0 If the network parameter "user.max_user_namespaces" is not equal to "0", or nothing is returned, this is a finding.

Check Text ( C-61557r942980_chk )

Verify RHEL 9 disables the use of user namespaces with the following commands:

Note: User namespaces are used primarily for Linux containers. If containers are in use, this requirement is Not Applicable.

$ sudo sysctl user.max_user_namespaces

user.max_user_namespaces = 0

If the returned line does not have a value of "0", or a line is not returned, this is a finding.

Check that the configuration files are present to enable this kernel parameter.

$ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|;)' | grep -F user.max_user_namespaces | tail -1
user.max_user_namespaces = 0

If the network parameter "user.max_user_namespaces" is not equal to "0", or nothing is returned, this is a finding.

Fix Text (F-61481r925434_fix)
Configure RHEL 9 to disable the use of user namespaces by adding the following line to a file, in the "/etc/sysctl.d" directory: Note: User namespaces are used primarily for Linux containers. If containers are in use, this requirement is Not Applicable. user.max_user_namespaces = 0 The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command: $ sudo sysctl --system

Fix Text (F-61481r925434_fix)

Configure RHEL 9 to disable the use of user namespaces by adding the following line to a file, in the "/etc/sysctl.d" directory:

Note: User namespaces are used primarily for Linux containers. If containers are in use, this requirement is Not Applicable.

user.max_user_namespaces = 0

The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command:

$ sudo sysctl --system