The Red Hat Enterprise Linux operating system must be configured so that the SSH daemon does not allow compression or only allows compression after successful authentication.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-204602	RHEL-07-040470	SV-204602r880758_rule		Medium

Description
If compression is allowed in an SSH connection prior to authentication, vulnerabilities in the compression software could result in compromise of the system from an unauthenticated connection, potentially with root privileges.

STIG	Date
Red Hat Enterprise Linux 7 Security Technical Implementation Guide	2022-12-06

Details

Check Text ( C-4726r880756_chk )
Note: For RHEL 7.4 and above, this requirement is not applicable. Verify the SSH daemon performs compression after a user successfully authenticates. Check that the SSH daemon performs compression after a user successfully authenticates with the following command: # grep -i compression /etc/ssh/sshd_config Compression delayed If the "Compression" keyword is set to "yes", is missing, or the returned line is commented out, this is a finding.

Check Text ( C-4726r880756_chk )

Note: For RHEL 7.4 and above, this requirement is not applicable.

Verify the SSH daemon performs compression after a user successfully authenticates.

Check that the SSH daemon performs compression after a user successfully authenticates with the following command:

# grep -i compression /etc/ssh/sshd_config
Compression delayed

If the "Compression" keyword is set to "yes", is missing, or the returned line is commented out, this is a finding.

Fix Text (F-4726r880757_fix)
Uncomment the "Compression" keyword in "/etc/ssh/sshd_config" (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor) on the system and set the value to "delayed" or "no": Compression no The SSH service must be restarted for changes to take effect.