Information
This variable Specifies the available MAC (message authentication code) algorithms. The MAC algorithm is used in protocol version 2 for data integrity protection. Multiple algorithms must be comma-separated.
Note: Some organizations may have stricter requirements for approved MACs. Ensure that MACs used are in compliance with site policy.
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