X displays must not be exported to the world.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-4697	GEN005200	SV-4697r2_rule	ECSC-1	High

Description
Open X displays allow an attacker to capture keystrokes and to execute commands remotely. Many users have their X Server set to xhost +, permitting access to the X Server by anyone, from anywhere.

STIG	Date
UNIX SRG	2013-03-26

Details

Check Text ( C-719r2_chk )
If X Windows is not used on the system, this is not applicable. Check the output of the xhost command from an X terminal. Procedure: $ xhost If the output reports access control is enabled (and possibly lists the hosts that can receive X Window logins), this is not a finding. If the xhost command returns a line indicating access control is disabled, this is a finding. NOTE: It may be necessary to define the display if the command reports it cannot open the display. Procedure: $ DISPLAY=MachineName:0.0; export DISPLAY MachineName may be replaced with an Internet Protocol Address. Repeat the check procedure after setting the display.

Check Text ( C-719r2_chk )

If X Windows is not used on the system, this is not applicable.

Check the output of the xhost command from an X terminal.

Procedure:
$ xhost
If the output reports access control is enabled (and possibly lists the hosts that can receive X Window logins), this is not a finding. If the xhost command returns a line indicating access control is disabled, this is a finding.

NOTE: It may be necessary to define the display if the command reports it cannot open the display.

Procedure:
$ DISPLAY=MachineName:0.0; export DISPLAY
MachineName may be replaced with an Internet Protocol Address. Repeat the check procedure after setting the display.

Fix Text (F-4625r2_fix)
If using an xhost-type authentication the xhost - command can be used to remove current trusted hosts and then selectively allow only trusted hosts to connect with xhost + commands. A cryptographically secure authentication, such as provided by the xauth program, is always preferred. Refer to your X11 server's documentation for further security information.