5.2.11 Ensure only approved MAC algorithms are used

Information

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/1861

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-13, CSCv6|3.4

Plugin: Unix

Control ID: 56ced1fb589869ace27b82d95ef99a53fc0a0b0dfb326093bcc3f4129c19b50b