5.3.34 Ensure SSH compressions setting is delayed

Information

Teh operating system must be configured so that the SSH daemon does not allow compression or only allows compression after successful authentication.

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.

Solution

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 :

Example: vim /etc/ssh/sshd_config

Add, uncomment or update the following line:

Compression no

The SSH service must be restarted for changes to take effect.

# systemctl restart sshd.service

See Also

https://workbench.cisecurity.org/benchmarks/8415

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6b.

Plugin: Unix

Control ID: 129c28357b81d5ff451112edd814f692ec1012ef586b95db39a5c56a980c674e