5.2.14 Ensure only strong MAC algorithms are used - weak MAC algorithms

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 and add/modify the MACs line to contain a comma
separated list of the site approved MACs
Example:

MACs [email protected],[email protected],hmac-sha2-512,hmac-sha2-256

Default Value:

MACs [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1,[email protected]

See Also

https://workbench.cisecurity.org/files/2420

Item Details

Category: IDENTIFICATION AND AUTHENTICATION, SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|IA-5, 800-53|SC-8, CSCv6|3.4, CSCv7|14.4, CSCv7|16.5

Plugin: Unix

Control ID: c0eb2bb3165cde599e2de80ca6273c01a63ca107033e4034fca89b02af29bc61