5.2.11 Ensure only approved MAC algorithms are used

Information

This variable limits the types of MAC algorithms that SSH can use during communication.

Rationale:

MD5 and 96-bit MAC algorithms are considered weak and have been shown to increase exploitability in SSH downgrade attacks. Weak algorithms continue to have a great deal of attention as a weak spot that can be exploited with expanded computing power. An attacker that breaks the algorithm could take advantage of a MiTM position to decrypt the SSH tunnel and capture credentials and information

Solution

Edit the /etc/ssh/sshd_config file to set the parameter in accordance with site policy. The following includes all supported and accepted MACs:

MACs hmac-sha2-512,hmac-sha2-256

See Also

https://workbench.cisecurity.org/files/3738

Item Details

Category: IDENTIFICATION AND AUTHENTICATION, SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|IA-5, 800-53|SC-8, CSCv7|14.4, CSCv7|16.5

Plugin: Unix

Control ID: d7ca27be0d4b9a92829cf5d91c9f16cf71721e36c2317603ca488c1817a394b3