Title

TOSS must force a frequent session key renegotiation for SSH connections by the client. (Cat II impact)

Discussion

Without protection of the transmitted information, confidentiality and integrity may be compromised because unprotected communications can be intercepted and either read or altered. This requirement applies to both internal and external networks and all types of information system components from which information can be transmitted (e.g., servers, mobile devices, notebook computers, printers, copiers, scanners, and facsimile machines). Communication paths outside the physical protection of a controlled boundary are exposed to the possibility of interception and modification. Protecting the confidentiality and integrity of organizational information can be accomplished by physical means (e.g., employing physical distribution systems) or by logical means (e.g., employing cryptographic techniques). If physical means of protection are employed, then logical means (cryptography) do not have to be employed, and vice versa. Session key regeneration limits the chances of a session key becoming compromised.

Check Content

Verify the SSH client is configured to force frequent session key renegotiation with the following command: $ sudo grep -i RekeyLimit /etc/ssh/ssh_config RekeyLimit 1G 1h If "RekeyLimit" does not have a maximum data amount and maximum time defined, is missing or commented out, this is a finding.

Fix Text

Configure the system to force a frequent session key renegotiation for SSH connections by the client by add or modifying the following line in the "/etc/ssh/ssh_config" file: RekeyLimit 1G 1h Restart the SSH daemon for the settings to take effect. $ sudo systemctl restart sshd.service

Additional Identifiers

Rule ID: SV-253057r958408_rule

Vulnerability ID: V-253057

Group Title: SRG-OS-000033-GPOS-00014

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.