The sshd server must bind the X11 forwarding server to the loopback address.
An XCCDF Rule
Description
<VulnDiscussion>As enabling X11 Forwarding on the host can permit a malicious user to secretly open another X11 connection to another remote client during the session and perform unobtrusive activities such as keystroke monitoring, if the X11 services are not required for the system's intended function, they should be disabled or restricted as appropriate to the user's needs. By default, sshd binds the forwarding server to the loopback address and sets the hostname part of the DISPLAY environment variable to “localhost”. This prevents remote hosts from connecting to the proxy display.</VulnDiscussion><FalsePositives></FalsePositives><FalseNegatives></FalseNegatives><Documentable>false</Documentable><Mitigations></Mitigations><SeverityOverrideGuidance></SeverityOverrideGuidance><PotentialImpacts></PotentialImpacts><ThirdPartyTools></ThirdPartyTools><MitigationControl></MitigationControl><Responsibility></Responsibility><IAControls></IAControls>
- ID
- SV-233301r603283_rule
- Severity
- Medium
- References
- Updated
Remediation - Manual Procedure
The root role is required.
Modify the sshd_config file.
# vi /etc/ssh/sshd_config